Climate change impact on
groundwater resources
in Australia
OV Barron, RS Crosbie, SP Charles, WR Dawes,
R Ali, WR Evans,R Cresswell, D Pollock,
G Hodgson, D Currie, F Mpelasoka, T Pickett,
S Aryal, M Donn and B Wurcker
Waterlines Report Series No 67, December 2011
(Photo)
NATIONAL WATER COMMISSION — WATERLINES
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Waterlines
This paper is part of a series of works commissioned by the National Water Commission on
key water issues. This work has been undertaken by CSIRO Water for a Healthy Country
Flagship on behalf of the National Water Commission.
© Commonwealth of Australia 2011
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Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by
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and rights should be addressed to the Communications Director, National Water Commission, 95 Northbourne Avenue, Canberra ACT 2600 or email bookshop@nwc.gov.au.
Online/print: 978-1-921853-51-7
Climate change impact on groundwater resources in Australia December 2011
Authors: OV Barron, RS Crosbie, SP Charles, WR Dawes, R Ali, WR Evans, R Cresswell, D Pollock, G Hodgson, D Currie, F Mpelasoka, T Pickett, S Aryal, M Donn and B Wurcker
Published by the National Water Commission
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Tel: 02 6102 6000
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Date of publication: December 2011
Cover design by: Angelink
Front cover image of Murray River, Swan Reach SA (right): Arthur Mostead
An appropriate citation for this report is:
Barron OV et al, 2011 Climate change impact on groundwater resources in Australia Waterlines report, National Water Commission, Canberra.
Disclaimer
This paper is presented by the National Water Commission for the purpose of informing
discussion and does not necessarily reflect the views or opinions of the Commission.
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Contents
Executive summary
1. Introduction
2.
3.
4.
5.
xi
1
Scope of this report
Sensitivity of groundwater resources to climate change
Renewable groundwater resources
Non-renewable groundwater resources
Investigation of climate change impact on groundwater resources
2
3
4
7
7
Climate in Australia and projected change
9
Observed distribution of climate types and changes over the last 80 years
Projections of future climate change and the effect on extent of Köppen-
Geiger
climate types occurrence
Variability and uncertainty in climate projections from different downscaling
approaches
Conclusions
9
21
23
Aquifer characterisation and prioritisation
24
Characterising aquifer sensitivity to climate change
Aquifer prioritisation
Prioritisation factors
Aquifer definition and data sources
Prioritisation results
Notable exclusions
Comparision with other prioritisation studies
Priority aquifers
Limitations and recommendations for further aquifer prioritisation
24
24
24
28
30
36
37
37
39
Effect of climate types and climate change on potential groundwater recharge
41
Diffuse groundwater recharge under the historical climate
Specifics of diffuse groundwater recharge under various climate types
Upscaling the point scaling modelling to a national coverage
Diffuse groundwater recharge under a future climate
Projected changes in recharge under selected GCMs
Relationship between change in rainfall and change in recharge
Effect of climate change and climate variability on recharge
Effect of climate change on localised recharge
Approach to the evaluation of localised recharge change under changing
climate
Projected changes in the river flow
Projected changes in localised recharge
Conclusions
41
42
50
51
51
55
57
58
Climate change impacts on groundwater resources in different aquifer types
74
Hydrogeological setting of modelled aquifers
Relationship to national aquifers characterisation
Recharge and discharge processes
76
77
77
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61
63
65
71
iv
Review of model results
Modelling historical conditions
Modelling future scenarios
Effect of climate change on groundwater resource
Discussion
Modelling climate change with groundwater models
Conclusions
78
78
80
84
86
87
89
6.
Climate change impacts on groundwater resources, environment, agriculture and water supply in key aquifers of Australia
91
High-priority aquifers—brief description
Lachlan
Newer Volcanics
Upper Condamine and Border Rivers Alluvium
Atherton Tablelands
Coastal River Alluvium 1
Toowoomba Basalts
Gunnedah
Pilbara
Port Campbell Limestone
Coastal River Alluvium 4
Coastal Sands 4
Otway Basin
Adelaide Geosyncline 3
Daly Basin
Climate change impacts on rainfall and diffuse recharge
Climate change impacts on agriculture, water supply and environment
Lachlan
Newer Volcanics
Upper Condamine and Border Rivers Alluvium
Atherton Tablelands
Coastal River Alluvium 1
Toowoomba Basalts
Gunnedah
Pilbara
Port Campbell Limestone
Coastal River Alluvium 4
Coastal Sands 4
Otway Basin
Adelaide Geosyncline 3
Daly Basin
Summary
Conclusions
91
92
94
97
98
99
100
100
102
103
104
105
106
107
108
109
114
115
119
119
120
121
121
122
122
123
124
124
125
125
125
126
131
7.
Recommendations for groundwater management and planning processes to cope
with climate change133
Recharge-rainfall relationship and sensitivity of recharge to changes in rainfall
Future climate impacts on rainfall
Future climate impacts on diffuse recharge
Future climate impacts on interaction with surface water
Priority aquifers
Groundwater use and effect on dependent industries
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135
136
137
138
141
v
Knowledge advancement required to better project future climate changes
on groundwater resources
Appendix 1 to Chapter 2: Projections of future climate change
Appendix 2 to Chapter 3: Priority Aquifers
Appendix 3 to Chapter 4: Diffuse groundwater recharge under various
climate types
Appendix 4 to Chapter 4: Effect of climate change on localised recharge
Method
Results
Localised recharge associated with floods (Chowilla floodplain)
142
147
150
156
163
165
169
193
References
198
Figures
Figure 1: Current climate parameters: a) Köppen-Geiger climate zones; b) mean annual
temperature; c) mean annual precipitation; d) proportion of summer precipitation........................11
Figure 2: Observed historical 1930–2010 trends: a) gridded precipitation (mm/yr) and b)
o
temperature ( C/yr) .........................................................................................................................12
Figure 3: Historical series of Australian Köppen-Geiger climate type maps derived for 1930–
1960, 1940–1970, 1950–1980, 1960–1990, 1970–2000 and 1980–2010 .....................................13
Figure 4: Changes in the areas (as percentage of Australia land) with observed climate types
for time periods shown in Figure 3 plotted against the end year of the considered periods ..........14
Figure 5: Percentage change in annual average rainfall projected from each GCM for a future
climate (~2030) relative to the historical climate under a medium global warming scenario
(+1.0°C) ..........................................................................................................................................16
Figure 6: As in Figure 5, but for a ~2050 medium global warming scenario (+1.7°C) ........................17
Figure 7: Precipitation scaling factors (PSF): change in annual average rainfall projected for
wet, median and dry future climate scenarios for 2030 (top row) and 2050 (bottom row)
relative to baseline..........................................................................................................................18
Figure 8: 2050 medium global warming projections: a) mode climate type; b) frequency of the
mode climate type; 0—no difference, 1—different; c) mode climate type compared to
baseline climate type; d) number of different projected climate types ...........................................19
Figure 9: Areal percentage of projected climate types over Australia against degrees of global
warming ..........................................................................................................................................20
Figure 10: Current land cover overlain with mode projected climate type transition zones for
the a) 2030 and b) 2050 medium global warming projections .......................................................20
Figure 11: Boxplots of the change in rainfall projected at three sites for the IPCC A2 scenario
comparing differences in GCMs and downscaling methods (note: there are only three
points in the box for the top row of plots and five points in the bottom row) ..................................22
Figure 12: Major aquifer systems of Australia—assessment units for the prioritisation scheme ........29
Figure 13: Aquifer prioritisation results for individual metrics: a) E/Emax; b) SY/SYmax; c)
f(baseflow GDEs); d) f(other GDE types); e) E/SY; f) aquifer responsiveness for f(R:S) ..............31
Figure 14: Plot of aquifer sensitivity rank versus importance rank. Orange shading indicates
selection of priority aquifers, green shading indicates selection of sensitive aquifers (of low
importance rating), blue shading indicates selection of important aquifers (of low sensitivity
rating)..............................................................................................................................................32
Figure 15: Map showing location of priority aquifers ...........................................................................35
Figure 16: Plot of prioritisation ranks shown by aquifer type and zone. Climate zone
classification based on grouping of Köppen-Geiger codes as follows: 1) Tropical = Af, Am,
Aw; 2) Arid/Semi-arid = BWh, BWk, BSh, BSk; 3) Mediterranean = Csa, Csb; (4) Humid
subtropical = Cwa, Cfa; (5) Temperate = Cfb, Cfc, Dfb, Dfc ..........................................................35
Figure 17: Left: Köppen-Geiger climate types of Australia as defined by Peel et al. (2007)
using the climate from 1930–2009 (Barron et al. 2010). Right: Simplified climate zones
used in the modelling and the control points used for the point scale modelling ...........................42
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Figure 18: Relative importance of climate characteristics within considered climate types
under various soil and vegetation ........................................................................................................ 45
Figure 19: Relationship between relative importance of rainfall and mean annual rainfall within considered climate types for perennial vegetation and soil with K~1 m/day ....................................... 46
Figure 20: Relationship between relative importance of temperature, VPD and solar radiation
(cumulatively) and mean annual rainfall within considered climate types for perennial
vegetation and soil with K~1 m/day ..................................................................................................... 46
Figure 21: Relationship between a) modelled recharge and mean annual rainfall, and b) between per cent recharge in rainfall and mean annual rainfall for perennial vegetation and
soil with K~1 m/day .............................................................................................................................. 47
Figure 22: Modelled historical annual average recharge across Australia for the period 1930–
2009 expressed in mm/yr (left) and as a percentage of rainfall (right) ................................................ 50
Figure 23: Variability in recharge throughout the 80-year baseline scenario. The wet, median
and dry 15-year periods within the historical climate scenario compared to the 80-year
annual average recharge plotted as a recharge scaling factor (RSF). ................................................ 51
Figure 24: RSF rasters for the medium global warming scenario using an 80-yr baseline ...................... 52
Figure 25: Number of RSF rasters that project a decrease in recharge from the 16 GCMs for each global warming scenario ............................................................................................................. 53
Figure 26: The 10%, 50% and 90% exceedences from fitting the RSF rasters to a weighted Pearson Type III distribution for each global warming scenario. The blacked-out areas are
where the change in recharge is not statistically significant. ............................................................... 54
Figure 27: A comparison of the RSF for a 2030 climate from the sustainable yields projects
and the RSF for a 2050 climate from the current project .................................................................... 55
Figure 28: Examples of the relationship between the change in rainfall and the change in recharge at Tomago (NSW) and Gnangara (WA) for each global warming scenario using
all 16 GCMs (point-scale modelling). No line is plotted at Gnangara for the high global
warming scenario as the relationship is not statistically significant. .................................................... 56
Figure 29: Change in rainfall–change in recharge relationships under a 2050 climate. The
areas shaded black are where the relationship is not statistically significant...................................... 57
Figure 30: A matrix of 12 RSF rasters comprised of four different climates (dry, median and
wet future climate and historical climate) and 15-year variabilities (dry, median and wet) for
the 80-year baseline ............................................................................................................................ 58
Figure 31: Wet, median and dry (from left to right) estimates of change in future mean annual
o
runoff for a 1 C global warming (~2030 relative to 1990) (Chiew 2010) ............................................. 59
Figure 32: Flood change map for the Murray-Darling Basin under historical, current (Scenario
A) and future (median future climate scenario) MDBSY modelled scenarios (adopted from
Overton et al. 2010); note that current scenario (Scenario A) is not used in this project .................... 60
Figure 33: Location of stations along the losing streams analysed for effects of climate
change on river discharge ................................................................................................................... 62
Figure 34: Presentation of the modelled flow data for a) historical and future climate scenarios
and b) flow changes under future climate scenarios relative to historical river flow ........................... 63
Figure 35: Average change in streamflow across all flow frequencies relative to streamflow
under the historical climate for the selected rivers .............................................................................. 64
Figure 36: Average change in rainfall for all future climate change scenarios from the
historical climate at regions representing the 15 chosen stations ....................................................... 64
Figure 37: Changes in streamflow with 10 per cent exceedence probability for three future climate scenarios (future dry, median and wet climate) relative to historical climate .......................... 64
Figure 38: Per cent of time with no flow at the station; streams with zero values are the
perennial stream .................................................................................................................................. 65
Figure 39: Changes in the Murrumbidgee River flow and the range of changes in localised
recharge for dry, median and wet future climate scenarios ................................................................. 66
Figure 40: Average changes in the localised recharge across all flow frequencies relative to localised recharge under the historical climate for the selected rivers (for Hgw = 1 m) ........................ 67
Figure 41: Relationship between sensitivity of localised recharge, e, to changes in river flow, and daily river discharge under historical climate conditions (for Murrumbidgee River) ..................... 67
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Figure 42: Sensitivity of localised recharge to changes in river flow for various initial depths to
groundwater, which remain unchanged under the future scenarios (for Murrumbidgee
River) .............................................................................................................................................. 67
Figure 43: Sensitivity of localised recharge to changes in river flow for various changes in depth to groundwater (for Murrumbidgee River): 1m watertable depth was assumed for the
historical scenario ........................................................................................................................... 68
Figure 44: Sensitivity of localised recharge to changes in river flow for various river slopes (for Murrumbidgee River) ...................................................................................................................... 68
Figure 45: Changes in localised recharge under future climate scenarios defined for a composite trapezoidal channel (the river channel remains unchanged and hence a single
line is associated with the period of river flow contained within the channel; the only
changes are associated with floodplain width, and changes in recharge during flooding are
shown in green and pink colour for narrow and wide floodplains): a) for dry future climate;
b) for medium future climate; and c) for wet future climate ............................................................ 69
Figure 46: The location of the Chowilla floodplain, a) the recharge estimates used to
determine climate change impacts on localised recharge derived from flood inundation
events and b) the extent of inundation for given flow rates (Overton et al. 2006).......................... 70
Figure 47: Duration curves for a) Chowilla daily river flow (426510) for historical, future dry
and future medianclimate scenarios and b) estimated recharge volumes from floodplain
inundation under those climate scenarios ...................................................................................... 71
Figure 48: Projected changes in recharge volumes (dR) and river flow (dQ) from floodplain inundation for future median and future dry climate scenarios relative to historical climate .......... 71
Figure 49: Location of the reviewed groundwater models................................................................... 75
Figure 50: Proportion of point localised and diffuse input components to groundwater models, under fitted historical conditions ..................................................................................................... 79
Figure 51: Proportion of discharge components from groundwater models under fitted historical conditions. Negative values are a net discharge flux, positive values are a net
gain to the system. ......................................................................................................................... 80
Figure 52: Percentage change in a) recharge and b) discharge water-balance components for alluvial aquifers of the MDB under a median future climate. All changes are relative to the
absolute fitted values from the historical simulation. ...................................................................... 81
Figure 53: Percentage change in a) recharge and b) discharge water-balance components for sedimentary aquifers of NT, WA and Tasmania under a median future climate. All changes
are relative to the absolute fitted values from the historical simulation. ......................................... 82
Figure 54: Percentage change in a) recharge and b) discharge in the water balance for alluvial aquifers of the MDB under a dry future climate. All changes are relative to the
absolute fitted values from the historical simulation. ...................................................................... 83
Figure 55: Percentage change in a) recharge and b) discharge input water balance components for sedimentary aquifers of NT, WA and Tasmania under a dry future climate.
All changes are relative to the absolute fitted values from the historical simulation. ..................... 84
Figure 56: Map showing the location of high-priority aquifers ............................................................. 92
Figure 57: Rainfall-scaling factors under the wet, median and dry future climates in the high-
priority aquifers ............................................................................................................................. 113
Figure 58: Recharge-scaling factors under the wet, median and dry future climates in the high-priority aquifers ..................................................................................................................... 113
Figure 60: Groundwater use as per cent of total water extraction in high-priority aquifers ............... 127
Figure 59: Groundwater use by agriculture and others, total use and sustainable yield of high-
priority aquifers ............................................................................................................................. 127
Figure 61: Map showing location of extreme recharge scaling factors expected under the future median climate scenario. ................................................................................................... 140
Figure 62: Map showing location of priority, sensitive and important aquifers .................................. 141
Figure 63: Change (°C) in annual average temperature projected from each GCM for a future climate (~2050) relative to the historical climate under a medium global warming scenario
(+1.7°C) ........................................................................................................................................ 147
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Figure 64: Change (%) in annual average relative humidity projected from each GCM for a
future climate (~2050) relative to the historical climate under a medium global warming
scenario (+1.7°C) ............................................................................................................................... 148
Figure 65: Change (%) in annual average solar radiation projected from each GCM for a future climate (~2050) relative to the historical climate under a medium global warming
scenario (+1.7°C) ............................................................................................................................... 149
Figure 66: Recharge as a mean value within the major climate types for various soil and vegetation types; in legend AP–annual vegetation, PP–perennial vegetation and TR–trees ........... 156
Figure 67: Per cent recharge in annual rainfall as a mean value within the major climate types
for various soil and vegetation types; in legend AP–annual vegetation, PP–perennial
vegetation and TR–trees ................................................................................................................... 157
Figure 68: Relationship between relative importance of rainfall and mean annual rainfall .................... 158
Figure 69: Relationship between relative importance of temperature, VPD and solar radiation
(cumulatively) and mean annual rainfall for soil with K~1 m/day ...................................................... 158
2
Figure 70: Changes in the correlation coefficient ( R ) of recharge/rainfall relationship and
mean annual rainfall within the major climate types .......................................................................... 159
Figure 71: Relationship between per cent recharge in annual rainfall and mean annual rainfall
within the major climate types ........................................................................................................... 160
Figure 72: Recharge elasticity and mean annual rainfall within considered climate types for perennial vegetation and soil with K~1 m/day ................................................................................... 161
Figure 73: Changes to per cent of high intensity rainfall in total annul rainfall from north to south of the continent: a) daily rainfall greater than 20 mm; b) moving average over 14 days with daily 5 mm threshold; and c) moving average over 21 days with daily 5 mm
threshold ............................................................................................................................................ 162
Figure 74: Example of daily recharge event and recharge volume distributions indicating
episodic recharge .............................................................................................................................. 163
Figure 75: Example of connected and disconnected groundwater system (Source: Brunner et
al. 2009) ............................................................................................................................................. 164
Figure 76: Method flow chart .................................................................................................................. 166
Figure 77: Relationship between river flow and river stage under for a range of river widths................ 167
Figure 78: Relationship between recharge and river flow for a range of river widths ............................ 167
Figure 79: Per cent changes in recharge for various river widths under changes in river flow (green lines are related to an individual river widths shown on Figure 77 and Figure 78, with the lowest line associated with the smallest width; the red line indicates the same river
flow) ................................................................................................................................................... 168
Figure 80: Changes in the river flow (red line) and the range of changes in localised recharge
(shown as a green area) for dry, median and wet future climate scenarios for all
considered stations (as listed in Table 16) ........................................................................................ 184
Figure 81: Relationship between localised recharge sensitivity e = dR/dQ and river flow
(upper) and e = dR/dQ and flow exceedence probability (lower) under historical climate
conditions (for selected stations, as listed in Table 16). The results are given for various
depths to groundwater, which are assumed to be constant between historical and future
climate scenarios ............................................................................................................................... 192
Figure 82: Flow duration curve for Chowilla daily river flow (426510) for historical, future median andwetclimate scenarios ...................................................................................................... 194
Figure 83: Changes in the inundation area and associated average recharge under various
river flows ........................................................................................................................................... 195
Figure 84: Projected changes in recharge volumes (dR) and river flow (dQ) from floodplain inundation for future median and future dry climate scenarios relative to historical climate:
a) based on floodplain data; b) based on the method described in Figure 76. ................................. 196
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Tables
Table 1: Characteristics of selected climate zones ............................................................................. 10
Table 2: Global climate models used in this study .............................................................................. 15
Table 3: Aquifer types and their general sensitivity to changes in climate .......................................... 26
Table 4: Prioritisation results—sensitive, important and priority aquifers* (showing in the
collours as in ................................................................................................................................... 34
Table 5: Trends noted in Figure 16 ..................................................................................................... 36
Table 6: Priority aquifers by aquifer type and climate zone................................................................. 39
Table 7: Climate types and recharge ................................................................................................... 48
Table 8: Different climate types in the high-priority aquifers shown as per cent of the total
aquifer area. ................................................................................................................................... 95
Table 9: Main soil types in the high-priority aquifers shown as per cent of the total aquifer area
(Johnston, et al., 2003) ................................................................................................................... 96
Table 10: Main land uses in the high-priority aquifers shown as per cent of total aquifer area .......... 96
Table 11: Statistics of 80-year baseline period rainfall and wet, median and dry future climates
for the priority aquifers .................................................................................................................. 110
Table 12: Mean annual recharge rates under the baseline historical period and RSF under the
historical, wet, median and dry future climates ............................................................................ 111
Table 13: Groundwater use categories, allocation and utilisation levels and expected changes
in diffuse recharge under future climates in high-priority aquifers ............................................... 116
Table 14: Recharge, discharge mechanisms and storage dynamics in high-priority aquifers .......... 129
Table 15: Recommendations for the required management response, monitoring and assessment in each of the priority aquifers .................................................................................. 144
Table 16: List of gauging stations along the losing streams underlain by the priority aquifers. Some of the stations are outside of the priority aquifers. ............................................................. 165
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Abbreviations and acronyms
AR4
Fourth Assessment Report of the Intergovernmental Panel on Climate
Change
BOM
Bureau of Meteorology, Australia
CCAM
Cubic Conformal Atmospheric Model
CO2
carbon dioxide
CSIRO
Commonwealth Scientific and Industrial Research Organisation
EC
electrical conductivity
FDC
flow duration curve
GAB
Great Artesian Basin
GCM
global climate model
GDE
groundwater-dependent ecosystem
GMU
groundwater management unit
IOCI
Indian Ocean Climate Initiative
IPCC
Intergovernmental Panel on Climate Change
MDB
Murray–Darling Basin
MDBA
Murray–Darling Basin Authority
MDBSY
Murray–Darling Basin Sustainable Yields Project
NASY
Northern Australia Sustainable Yields Project
NGAP
National Groundwater Action Plan
NWI
National Water Initiative
PHRAMS
Peel–Harvey Regional Aquifer Modelling System
PRAMS
Perth Regional Aquifer Modelling System
PSF
precipitation (rainfall) scaling factor
RSF
recharge scaling factor
SEACI
South Eastern Australian Climate Initiative
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SRP
Southern Riverine Plains
SVAT
soil-vegetation-atmosphere-transfer model
SWAMS
South-West Aquifer Modelling System
SWWA
south-west Western Australia
SWWASY
South-West Western Australia Sustainable Yields Project
TasSY
Tasmania Sustainable Yields Project
TCSA
Tertiary Confined Sands Aquifer
TDS
total dissolved solids
TLA
Tertiary Limestone Aquifer
VFM
vertical flux model
VPD
vapour pressure deficit
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Executive summary
Over the past few decades, much of Australia has experienced increasing pressure on
groundwater resources due to a drier climate and increased scarcity of surface water. In 2004
the Council of Australian Governments agreed to form a National Water Initiative (NWI) to
ensure the implementation of a transparent planning framework that would avoid
overallocation of water resources, including groundwater. Under the NWI it is necessary to
incorporate risks associated with climate change and variability in water management plans.
In response to these issues, the National Water Commission commissioned a project,
‘Investigating the impact of climate change on groundwater resources’, within the National
Groundwater Action Plan. The primary objective of the project was to determine how
projected climate change will impact on groundwater recharge and groundwater resources
across different aquifer types in different climatic types across Australia.
Nationwide, historical (observed) and future (projected) climate data was used to assess
diffuse groundwater recharge (recharge associated with rainfall across the landscape) under
the different climate types. Some discussion of the climate change impact on localised
groundwater recharge associated with water losses from rivers and floodplains was also
provided.
In agreement with previous studies, annual rainfall is the most important climate parameter to
estimate recharge. However, the effect of temperature, solar radiation and vapour-pressure
deficit on recharge is particularly important in the regions with low annual recharge (including
arid climate zones), and also noticeable under climate types with summer-dominated rainfall
(i.e. northern Australia).
A common estimation of renewable groundwater resources is to assume a proportion of
rainfall each year generates recharge. Observations and modelling, however, have shown
that this method has a number of shortcomings. In particular, this analysis has revealed a
non-linearity in the recharge to rainfall ratio for any given location due to variability in rainfall
intensity or the number of consecutive rain days. Such interannual variability is more apparent
in areas of low recharge. Thus, compared to the long-term average, the variability of recharge
in different wet and dry 15-year periods is greater in areas of low recharge and comparatively
smaller in areas of high recharge. This means that interannual rainfall variability is magnified
two to four times in recharge variability. This so-called ‘recharge elasticity’ measure is higher
in the low recharge regions, i.e. arid zones.
Over the past 80 years Australian climatic trends have indicated warming over most of
Australia (except in the inland north-west), increasing rainfall over northern, central and north­
west Australia, and decreasing rainfall in eastern, south-east and south-west Australia. This
has led to a southerly expansion of the tropical climate types in the far north together with a
contraction in the northern extent of the arid types. The arid types have expanded to the south
and south-east, with a corresponding contraction of temperate types to the coast.
The projected future climates were inferred from 16 global climate models (GCMs) of the
Intergovernmental Panel on Climate Change (IPCC) 4th Assessment Report (AR4). The full
range of IPCC AR4 future climate projections was accounted for by scaling these 16 GCM
results according to three global warming scenarios (low, medium and high) for both 2030
and 2050. The modelling uncertainties in trend and magnitude of regional rainfall changes
limit our ability to provide confident assessments of likely impacts for many regions of
Australia. Projections are most consistent, however, for south-west Western Australia and the
southern Murray–Darling Basin, where all GCMs project a decrease in rainfall. As climate
xiii
data is an input to all further modelling, subsequent analysis will further propagate these
uncertainties.
Projected future changes in the spatial distribution of climate types indicate a further increase
in aridity at the expense of temperate coverage. For southern Australia the projections are
more consistent with observed trends in climate types over the past 80 years than are those
for northern Australia. As the projected warming and southern Australian rainfall decline
accelerates between 2030 and 2050, there is a possibility this will promote land-cover change
between now and 2050.
The median future climate at 2030 and 2050 projects a decrease in diffuse recharge across
most of the west, centre and south-east of Australia, while increases in recharge are
projected across northern Australia and a small area of eastern Australia. The relationship
between change in rainfall and change in recharge shows that the sensitivity of recharge to
change in rainfall is relatively constant under all global warming scenarios, but changes in
factors other than the total rainfall can result in a general overall increase in recharge with
increased global warming. These factors include temperature, rainfall intensity and carbon
dioxide-concentration effects on vegetation. As a result there was a trend of reduction in a
number of GCMs projecting a decrease in recharge with increased global warming over most
of the country. The south-west and some areas of the south-east are an exception, with all
GCMs projecting lower recharge under all future climate scenarios. Historical variability of
diffuse recharge over 15-year periods (within the 80-year baseline) is greater than the
magnitude of modelled recharge change under the future climate scenarios over an
equivalent 80-year average. This highlights the need for flexibility in water-sharing plans to
account for the compounding effect of current climate variability and future climate change.
Changes in localised recharge due to climate change are dependent on the level of
connectivity of rivers to the shallow aquifers. Projected changes in localised recharge from
disconnected losing streams were estimated to be similar to projected changes in river flow,
but lower than the projected changes in river flow from connected losing streams. Sensitivity
of localised recharge to changes in river flow reduces in areas with deeper groundwater (i.e.
disconnected systems). An increase in groundwater depth under future climate scenarios may
cause an increase in localised recharge from connected losing streams even under conditions
where river flow is projected to decrease. However, when overbank floods are the sources of
localised recharge, changes in localised recharge are likely to be much greater than projected
changes in river flow.
The effect of climate change on groundwater resources is influenced by the hydrogeological
setting of an aquifer. The project assessed all Australian aquifers in terms of their sensitivity
to climate change and their level of national importance, providing metrics that were used to
compare and contrast different aquifers and their climatic response across the country.
Fourteen priority aquifers were identified as both sensitive to climate and regionally important
and described in detail, including their geological setting, flow-system types, recharge and
discharge mechanisms, and current water use. These 14 aquifers occur across all climate
types and include most aquifer types.
Groundwater use as a percentage of total water use is above 80 per cent in six of these highpriority aquifers and ranges between 60 and 80 per cent in a further five high-priority aquifers,
highlighting the importance of these groundwater resources. Agriculture is the largest
groundwater user, followed by domestic and town water supplies, then commercial and
mining industries. In the Pilbara, however, the mining industry is the largest user. A future wet
scenario would see little or no impact either on groundwater users or the environment. Seven
priority aquifers might expect to be affected under the median scenario and most of the
priority aquifers might expect water shortages under a dry scenario.
xiv
In addition to the 14 priority aquifers, six aquifers in south-west Western Australia were also
included in our high-priority list. Although these aquifers were not identified as highly sensitive
to climate change, this region is projected to experience the greatest reduction in diffuse
recharge under a median or dry future climate.
Groundwater models are commonly used to investigate changes in the groundwater balance
due to projected climate change. Reviewing the results from a number of nationwide
programs (including state water authority programs, CSIRO sustainable yields projects and
Murray–Darling Basin Authority (MDBA) programs), where groundwater models were used to
apply projections of future climate change impacts on groundwater systems. Most were found
to be inadequate in assessing the future impacts of climate change. Modelling approaches,
model designs and the criteria used for groundwater resources sensitivity vary substantially
between the reviewed models. These made comparing the models’ outcomes and identifying
groundwater resources changes under future climate scenarios difficult. A key
recommendation of this work is that all groundwater models used in groundwater resource
management in Australia should undergo a climate change audit to ensure that they are fit­
for-purpose when proposing climate change-adaptation strategies. This study has highlighted
that some models are unsuitable for this purpose.
The outcomes of this project will contribute to an understanding of the impact of climate
change on groundwater management by considering the possible consequences of climate
change on groundwater resources across the country. This study was carried out at the
regional scale and considered only gross consequences at the aquifer level, and hence can
make only broad recommendations. Further and more detailed analysis at a scale
commensurate with resource utilisation on the ground should be undertaken.
The report summarises the project results, which are published in a series of companion
reports, including Barron et al. (2010), Crosbie et al. (2011a) and Currie et al. (2010). The
needs for further investigation and associated indicative costs for the 14 high-priority aquifers
are discussed in a separate report Summary of the costs of carrying out further quantitative
investigations in 20 priority aquifers.
xv
Introduction
In 2004, the Council of Australian Governments signed on to the National Water Initiative
(NWI). One of the aims of this initiative was to bring overallocated (that is, effectively overentitled) groundwater systems back to sustainable levels while developing a transparent
planning framework that would avoid future overallocation. Climate change adds a further
level of complexity to the management of over-entitled systems as the degree of overentitlement may change in the future. Where entitlements are reduced as a management
response, it is necessary, under a cost-sharing model, to assign the risk associated with
those changes. This risk assignment requires a good understanding of the climate change
processes impacting on water resources.
Australia has a highly varied and variable climate, with large regions having arid and semi­
arid climates. This has resulted in increasing pressures on groundwater resources as the
population has grown and development has taken place. The reduction in rainfall in many
Australian regions over recent years has seen both a reduction in recharge and an increase in
groundwater use as surface water resources have become scarce. Limited water resource
availability already constrains regional development in many parts of Australia, for both
industrial and agricultural activities. The future effects of climate change may add to these
constraints; quantifying the potential impacts of climate change on water availability, however,
is one of the most challenging components of long-term sustainable water management.
Climate change is of most concern where aquifers are either heavily allocated or particularly
vulnerable to changes in recharge. In these systems the reduction in water availability due to
climate change may impact on groundwater use and entitlements. The impacts of climate
change are also likely to be more profound for unconfined aquifer systems, which may
respond rapidly to changes in the recharge regime. The relationship between climate and
confined aquifer systems is often muted. In addition to consumptive use in many regions, a
rich biodiversity of both national and international significance is associated with groundwaterdependent ecosystems, which may also be impacted by changes to groundwater resources
because of a changing climate.
The Intergovernmental Panel on Climate Change (IPCC) 4th Assessment Report (AR4)
(2007) provided a global context for climate change, and included the outputs from a number
of global climate models (GCMs) under different greenhouse gas emission scenarios. CSIRO
has been further analysing climate change within the regional context, based on these IPCC
GCM outputs. The outcomes of some key CSIRO studies (the Indian Ocean Climate Initiative
), the South Eastern Australian Climate Initiative and the sustainable yields projects—
covering the Murray–Darling Basin (MDB), Tasmania and south-west Western Australia
(SWWA)) have shown a projected general reduction of rainfall across southern Australia, but
with an overall large variation in the magnitude of GCM rainfall projections across the entire
country.
Most national and international studies focus on climate change impacts to surface water
resources. Climate change effects on groundwater resources have not been systematically
assessed, despite many regions being greatly dependent on groundwater for irrigation,
industrial use (including mining) and urban water supply.
Key challenges in providing a national contextual statement on groundwater resources and
climate change include: sparse information on aquifers; poor understanding and quantification
of recharge and discharge mechanisms; lack of spatial appreciation of the connectivity to
streams; and unknown interactions with groundwater-dependent ecosystems. Most
groundwater management is based on long-term average recharge to the system. The effect
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1
of short- and long-term climate variability on groundwater resources is even less clear, both in
terms of groundwater recharge and discharge, which includes the groundwater uptake by
vegetation. This variability is compounded by potential climate change, which is currently not
considered in regional development plans.
In response to these pressing issues the National Water Commission (NWC) has
commissioned this project, ‘Investigating the impact of climate change on groundwater
resources’, within the National Groundwater Action Plan. Overall, the aim of this project is to
provide an Australia-wide snapshot quantifying the impacts of spatial and temporal change in
climate due to anthropogenic-induced global warming on groundwater resources for
representative aquifer systems.
Scope of this report
This project builds upon the work of CSIRO’s sustainable yield projects in the MDB and other
areas. The terms of references for the current project include:
a) Under different climate change scenarios, investigate and model the temporal variance of
rainfall, both intensity and frequency, temperature and associated changes in evaporation
and evapotranspiration, and the impacts these factors have on groundwater recharge and
resources across different aquifer types in different climatic zones in Australia. This will
need to include investigation and modelling of the impacts of temporal variance due to
climate change on recharge thresholds. Additionally, the project will investigate the impacts
of changes in surface water due to climate change on groundwater.
b) Investigate the impacts on the environment, agriculture and water supply in different
aquifers and climatic zones from any changes in groundwater recharge due to climate
change.
c) Under the investigation of climate change across different aquifer types in different climatic
zones, determine if climate change or other actions, such as land-use change, have a
greater impact on groundwater recharge.
The project activities were predominantly focused on investigating the effect of climate
change on groundwater recharge (Barron et al. 2010; Crosbie et al. 2011a; also Chapter 4 of
this report) and characterising Australian aquifers in terms of their sensitivity to climate
change and their level of national importance (Currie et al. 2010; also Chapter 3 of this
report).
Chapter 2 summarises our understanding of Australian climatic conditions and climate types
as well as their projected changes under the full range of IPCC AR4 future climate scenarios
for 2030 and 2050. The ranges and uncertainties in future climate projection from 16 GCMs
are discussed as are the resulting projected changes in climate-type distributions. In addition
to this Australia-wide assessment across the full range of projections, a more targeted
comparison of downscaling methods is undertaken for three locations using available daily
data for the IPCC’s Special Reports on Emmissions Scenarios (SRESR) A2 emissions
scenario.
Chapter 3 assesses Australian aquifers in terms of their sensitivity to climate and their level of
national importance, providing indices that might be used to compare and contrast aquifers
and their climatic response across the country. A list of priority aquifers that require more
detailed assessment has been generated.
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Chapter 4 investigates the climate sensitivity of diffuse recharge, both historically and into the
future. Historical (observed) and future (projected by GCMs) climate data was used to assess
scenarios of changes in current groundwater recharge rates nationwide. Chapter 4 also
provides a discussion on groundwater recharge within various climate types in Australia.
Some considerations of the climate change impact on localised groundwater recharge are
also provided.
Chapter 5 summarises and discusses the outcomes of a number of nationwide programs
(including state water-authority programs, CSIRO sustainable yields projects and Murray–
Darling Basin Authority (MDBA) programs) where groundwater models were developed and
applied to project the future climate impact on groundwater systems. This chapter also
summarises uncertainties and limitations related to these results and lists recommendations
for a groundwater-modelling approach suitable for climate change impacts assessment.
Chapter 6 presents the results of analyses for 14 priority aquifers, including a description of
their geological setting, flow-system types, recharge and discharge mechanisms, and current
water use. Based on a method developed within the project (Chapter 3), these aquifers were
defined as both sensitive to changes in climatic conditions being of high national importance.
Further discussion and suggestions for future work on these 14 aquifers are provided in a
separate report Summary of the costs of carrying out further quantitative investigations in 20
priority aquifers. That report also considers the current gaps in knowledge or data, and the
needs for and costs of further investigations.
Finally, Chapter 7 draws conclusions and recommendations for water managers on how best
to prepare for the impacts of climate change on Australia’s groundwater resources.
The effect of climate change on the quality of groundwater resources was considered to be
outside the scope of this project. Also excluded from consideration in this report was the
impact of climate change on recharge due to irrigation.
Sensitivity of groundwater resources to climate
change
The IPCC’s assessment reports are considered to be the authoritative reviews of climate
change research globally across all disciplines. The second assessment report made the
following comment about groundwater research (Watson et al. 1996):
Despite the critical importance of groundwater resources in many parts of the world, there
have been very few direct studies of the effect(s) of global warming on groundwater recharge.
Little had changed by the time the third assessment report was released five years later
(McCarthy et al. 2001):
Groundwater is the major source of water across much of the world, particularly in rural areas
in arid and semiarid regions, but there has been very little research on the potential effects of
climate change.
The fourth assessment came to a similar conclusion (Parry et al. 2007):
Despite its significance, groundwater has received little attention from climate change impact
assessments, compared to surface water resources.
Groundwater-resource sensitivities to climate change have been investigated in a number of
countries and continents (e.g. US: Rosenberg et al. 1999; Vaccaro 1992; Canada: Jyrkama
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3
and Sykes 2007; Toews and Allen 2009; UK: Herrera-Pantoja and Hiscock 2008; Africa:
Mileham et al. 2009). Also, some studies have attempted to generate a global estimation of
renewable groundwater resources (Doll 2009). These latter studies have demonstrated that
groundwater resources are exploited to a greater extent when surface water resources
decline under the pressure of a drying climate.
The most comprehensive studies of the impact of climate change on the water resources of
Australia have been carried out by the sustainable yields projects. These have reported on
the water resources of the MDB, northen Australia, south-west Western Australia and
Tasmania.
In this project, the term ‘resource’ covers the groundwater available to all users and uses
(including the environment). Two different types of resources are defined by the NWC:

Natural renewable groundwater resource: groundwater extracted from an aquifer that
receives recharge from rivers, rainfall or from other aquifers. It also refers to the total
amount of groundwater replenishment through the annual hydrological cycle, and therefore
has significant dependency on the climate and its variability, and is usually summarised on
a yearly basis.

Non-renewable groundwater resource (fossil): groundwater extracted from an aquifer that
receives limited or no recharge and therefore the extraction of such groundwater is referred
to as resource ‘mining’ or the use of long-term aquifer storage. These resources are
associated with usually deep aquifers that have a negligible rate of recharge on a human
timescale. Non-renewable resources are usually expressed either in terms of volumes or
extractable flow.
Extractable, or exploitable, groundwater resources may be further described as a component
of natural groundwater that is accessible for use. This definition is closely linked with the
concept of sustainable yield and is limited by the physical capacity to abstract groundwater,
together with consideration of environmental, social and economic values that may limit
groundwater use.
The sensitivity of groundwater resources to a changing climate may be defined by sets of
criteria, which differ for various types of resources. These are discussed below.
Renewable groundwater resources
Long-term average groundwater recharge is an accepted measure to help define a
‘renewable’ groundwater resource (Scanlon et al. 2002). Recharge can be broadly defined as
water that reaches an aquifer from above, below or laterally (Lerner et al. 1990). Most often,
however, it refers to downward water movement across a watertable. This can be either
diffuse (direct) recharge derived from precipitation or irrigation that occurs fairly uniformly over
large areas, or localised (indirect) recharge as concentrated input from inundation of
depressions in the surface topography such as streams, lakes and playas. Rushton (1997)
distinguishes actual recharge (water that reaches the watertable) from potential recharge
(water that has percolated below the root zone that may or may not reach the watertable).
Potential recharge is sometimes called deep drainage and is usually estimated from surface
water and unsaturated-zone studies.
The factors influencing diffuse groundwater recharge may be either dynamic, and controlled
by external forces such as climate, land use or vegetation, or static, and controlled by the
physical attributes of a particular aquifer system such as soil properties, geomorphology,
topography and geological setting. The static factors will determine the potential sensitivity of
a particular aquifer system to climate change for a given range of dynamic factors.
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Localised recharge occurs where there is an active surface water feature, particularly river
channels and floodplains, and where the groundwater level is lower than the water level in
those features. Localised recharge rates are controlled by the difference in water-pressure
head between the aquifer and the surface water, hydraulic properties of the land surface or
streambed and the effective width of the river. The processes of groundwater discharge to
surface water, and of surface water leakage to aquifers, are spatially and temporally complex,
particularly when the full extent of the system is taken into consideration. The rates,
seasonality and type of such interaction can vary under various landscapes and geological
settings (Reid et al. 2009).
The sensitivity of recharge to climate change is related to changes in rainfall amount and
intensity, the effect on vegetation from changes in temperature and carbon dioxide (CO 2), and
changes in localised recharge where climate change alters groundwater–surface water
interactions.
Diffuse recharge
It has been shown that rainfall is the most important climate parameter influencing
recharge, followed by rainfall intensity and temperature (McCallum et al. 2010). Furthermore,
changes in recharge induced by changes in CO2 concentration, solar radiation and vapour
pressure deficit are relatively minor.
Increases or decreases in recharge generally reflect increases or decreases in rainfall (Allen
et al. 2004; Serrat-Capdevila et al. 2007), but there are enough exceptions (Crosbie et al.
2010c; Doll 2009; Rosenberg et al. 1999) to preclude relying solely on change in rainfall as an
adequate predictor of change in recharge. Change in the frequency and seasonality of rainfall
may also influence changes in recharge. Vivoni et al. (2009) demonstrated for a catchment in
New Mexico that either an increase in the intensity of summer rainfall or an increase in the
frequency of winter rainfall can lead to an increase in recharge. In semi-arid areas, higher
intensity rainfall can lead to higher episodic recharge even under projections of decreased
total rainfall (Crosbie et al. 2010b; Ng et al. 2010).
The next most sensitive factor to influencing recharge is temperature. Most studies have been
for cold climates and are associated with variation in snowfall, snowmelt and frozen ground
under different temperature conditions (Eckhardt and Ulbrich 2003; Jyrkama and Sykes 2007;
Okkonen et al. 2010; Vivoni et al. 2009). For warmer climates, Rosenberg et al. (1999), for
example, found that recharge could decrease with an increase in rainfall due to higher
temperatures and higher evapotranspiration rates, such as in the Ogallala Aquifer. In the
Upper Nile Basin it was found that recharge increased as rainfall increased up to a 3°C
temperature increase. For larger temperature rises, however, evapotranspiration increases
lead to reductions in recharge (Kingston and Taylor 2010). Increased recharge was simulated
in the MDB despite a decrease in rainfall, which was attributed to a reduction in transpiration,
i.e. the transpiration reduced due to the effect of temperature on vegetation when the
optimum temperature for vegetation growth was exceeded (Crosbie et al. 2010c).
Recharge is generally much greater in non-vegetated than in vegetated regions (Gee et al.
1994), and greater in areas of annual crops and grasses than in areas of trees and shrubs
(Crosbie et al. 2010a). The impact of vegetation on recharge is evident in Australia, where
replacement of deep-rooted native eucalyptus trees with shallow-rooted crops resulted in
recharge increases of about two orders of magnitude, e.g. <0.1 mm/year for native mallee
vegetation to 5–30 mm/year for crop/pasture rotations (Allison et al. 1990).
An increase in CO2 affects plant growth and subsequently may also affect groundwater
recharge. Elevated CO2 allows plants to increase their water-use efficiency, thereby
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5
assimilating more carbon per unit of water transpired. This can lead to an increase in leaf
area, a reduction in transpiration, or both (Eckhardt and Ulbrich 2003; McCallum et al. 2010).
As the effect of vegetation on recharge can be significant, it is likely that if land use or land
cover were to change significantly because of climate change, the indirect effect of climate
change on recharge may be greater than that due to changes in rainfall or temperature alone.
Crosbie et al. (2010c) highlighted that the difference in recharge between vegetation systems
dominated by annuals, perennials and trees is greater than the projected changes in recharge
due to climate change alone in the MDB. Austin et al. (2010) assessed a land-use change
scenario where the entire MDB was reafforested. This unrealistic scenario, unsurprisingly,
produced much greater reductions in groundwater resources than climate change alone. van
Roosmalen et al. (2009) used a more plausible land-use change scenario, where areas of
grassland were converted to forest, and this had a very minor impact on recharge in an
environment where rainfall is much greater than potential evapotranspiration.
The actual sensitivity of the groundwater resources of individual aquifers to climate change is
further dependent on a variety of intrinsic factors, including the spatial distribution of soil
hydraulic properties in the aquifer’s recharge zone (including preferential pathways), aquifer
storage capacity and the distribution of aquifer hydraulic conductivity.
Localised recharge
Changes to localised recharge caused by climate change may have a significant impact on
groundwater resources where localised recharge comprises a large proportion of the total
aquifer recharge. This is most common in semi-arid to arid climates with a propensity for
episodic stream flow and major overbank flows, along with low diffuse recharge. Allen et al.
(2004) showed that the sensitivity of the Grand Forks Aquifer in south-central British
Columbia to climate-driven changes is particularly sensitive to changes in river stage. For a
scenario that simulated flood conditions of 50 per cent higher than average, the watertable
averaged 3.5 m higher than historical levels and there was an increase in volumes of surface
water leakage to surrounding aquifers.
The effect of a change in the rainfall distribution throughout the year may also influence
annual volumes of localised recharge. In southern British Columbia, Scibek and Allen (2006a)
showed that the effect on recharge of the projected shift in the hydrograph peak to an earlier
date—but with no change in the magnitude of the peak—is significant for an unconfined,
heterogeneous and highly permeable aquifer. For the aquifer. in which diffuse recharge was
the most significant recharge mechanism compared to localised recharge, only minor
changes to groundwater level were predicted.
Overbank floods are an important facet of localised recharge (Scibek and Allen 2006b), where
recharge volumes are driven by the frequency and intensity of flooding events and inundation
periods. These are likely to be sensitive to the frequencies and intensities of extreme rainfall
events-generated floods. Recharge volumes are commonly greater for the first flooding event
of the wet season when a greater proportion of flood water is infiltrating. Crerar et al. (1998)
showed, for ephemeral rivers in Namibia, that flood water during the first event comprised 6.9
per cent of localised reacharge but only 0.6 per cent for a later event of the same year.
Additional aquifer attributes that may influence localised recharge sensitivity to climate include
the level of river–aquifer connectivity, the proportion of localised recharge relative to diffuse
recharge to an aquifer, geomorphic setting (such as narrow or wide alluvial aquifers) and
mechanisms that promote rapid recharge, such as coarse-textured streambeds or karstic
features.
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6
There have been no studies to date of the impacts of climate change on localised recharge in
Australia.
Non-renewable groundwater resources
Strictly speaking, groundwater resources are never non-renewable. The timeframe for
replenishment, however, may be of the order of hundreds to thousands of years, and hence is
beyond the usable timeframe for reasonable water-resource planning. For this reason
utilisation of non-renewable groundwater can be considered as ‘mining of aquifer reserves or
storage’. The volumes of such groundwater stored in some aquifers can be very large. For
instance, the estimated groundwater storage in the Great Artesian Basin (GAB) is 64 900
3
3
km , compared to the renewable groundwater resource component of 0.35 km (AWR 2005).
Commonly, non-renewable resources are within confined aquifers, with limited recharge
areas, where groundwater development intercepts or induces little active recharge and the
piezometric surface falls continuously with abstraction (Foster and Loucks 2006). Such
groundwater systems occur particularly in semi-arid and arid regions. Non-renewable
groundwater can also include unconfined aquifers, in areas where contemporary recharge is
very infrequent or of small volume, and the resource is essentially limited to aquifer storage.
The distinction into renewable and non-renewable resources, however, is subjective and
there are some hydrogeological systems that can be hard to ascribe to one or the other. One
of them is a hydrogeological system with episodic recharge in which the recharge can occur
every decade or so, and they may be classified as renewable. However, it is often difficult to
predict the return period of recharge events. For example, aquifers in central Australia that
rely on major cyclone activity for recharge may not experience those events over decades,
and then have two or more cyclones active in their area over very short time periods. The
average annual recharge volume is thus highly dependent on the timescale of the observation
of recharge.
In contrast with renewable groundwater resources, non-renewable groundwater resources are
not generally dependent on the annual hydrological cycle or recent climate. The climate effect
on these resources may be indirect and associated with potentially increasing pressure on
groundwater abstraction as other water resources decline or as demand for water increases.
The measurement of the sensitivity of non-renewable groundwater resources to climate
change may therefore be estimated based on a parameter defining the relationship between
total groundwater resources to annual abstraction under future climate and changing water
demand (sensitive being defined as mean annual groundwater abstraction from non­
renewable sources being greater than 0.1 per cent of aquifer storage).
Investigation of climate change impact on
groundwater resources
Climate change impact on groundwater resources is commonly based on modelling of both
climate change projections and groundwater response to those changes.
The projections of climate variables under the future climate are derived from the outputs of
GCMs. Currently a range of GCM models (up to 25) are available (Meehl et al. 2007). Their
accuracy in reproducing historical climate in Australia varies (Smith and Chiew 2009) and
they also produce a wide range of projected changes in climate parameters under the future
climate. To better assess the range of possible future changes in climate, inclusion of a larger
GCM model suite is beneficial compared to a smaller suite of models.
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7
Because of their spatial coarseness GCM outputs are not directly suitable for further
hydrological analysis. To overcome this, downscaling methods were developed to transfer
GCM projections to the finer scale required by hydrological models. Techniques to transfer
GCM-scale information to the scale required for impacts-modelling can be broadly classified
into two categories: statistical downscaling and dynamical downscaling, which are described
in some detail in Maraun et al. (2010).
In the case of analysis related to climate change on groundwater resources, the projected and
downscaled climate time-series is used as input for groundwater recharge modelling to create
a time-series of projected future recharge. Recharge models used for the impact of
projections of climate change on recharge include HELP (Allen et al. 2004; Jyrkama and
Sykes 2007; Scibek and Allen 2006a; Scibek and Allen 2006b; Toews and Allen 2009),
SWAT (Eckhardt and Ulbrich 2003; Kingston and Taylor 2010; Rosenberg et al. 1999), EPIC
(Brouyère et al. 2004), SWAP (Ng et al. 2010) and WAVES (Crosbie et al. 2010c; Green et al.
2007; McCallum et al. 2010).
The diffuse recharge data is further applied as inputs to a groundwater model as a series of
possible scenarios. MODFLOW is by far the most commonly used groundwater model (Allen
et al. 2004; Candela et al. 2009; Croley and Luukkonen 2003; Hanson and Dettinger 2005;
Scibek and Allen 2006a; Scibek and Allen 2006b; Scibek et al. 2007; Serrat-Capdevila et al.
2007; Toews and Allen 2009; Woldeamlak et al. 2007). However, integrated models that
solve the water balance in the unsaturated zone, saturated zone and river channel all within
the one model are likely to be superior. Examples of models that have been used for studies
of climate change impacts on groundwater include MIKE-SHE (van Roosmalen et al. 2009);
HydroGeoSphere (Goderniaux et al. 2009) or MODHMS (Barr and Barron 2009). Limitations
on model use are commonly associated with the limitations of the significant sets of
parameters; their spatial variability and, commonly, the substantial computational time
required for model runs. However, these models allow a process-based simulation of surface
and groundwater interaction and are likely to better account for alteration in localised
recharge under changing climate conditions.
In summary, the primary indicator of groundwater resource potential is the amount and rate of
recharge to individual aquifers. This recharge is dependent on specific factors that are
variably influenced by climate change. The sensitivity of recharge to climate change is related
to changes in rainfall amount and intensity, the effect on vegetation from changes in
temperature and CO2, and changes in localised recharge where climate change alters
groundwater–surface water interactions.
Further, a distinction can be made between renewable and non-renewable resources and
their individual sensitivity to climate change. The key renewable resources of Australia, within
a climate change context, are identified in the following chapters and analysed in terms of
their importance and sensitivity.
Non-renewable groundwater resources are discussed sparingly in the following chapters and
have not undergone further analysis once they have been identified.
This project provides a regional perspective on climate change impacts on groundwater
resources. It is also clear that much work still needs to be done on characterising the climate
change impacts on Australia’s groundwater resources at the local level. There are few studies
at the local scale across Australia. Without these building blocks, more definitive conclusions
at the management level will be lacking.
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8
1. Climate in Australia and projected
change
As discussed above, groundwater resource sensitivity to climate change is dependent on both
the hydrogeological setting of the aquifer and variations in climate conditions. This chapter
focuses on Australian climate and climate change projections used to estimate changes to
renewable groundwater resources under projected future climate. It includes a description of
the historical climate using a Köppen-Geiger classification of climate types, the projection of
future climate and the resulting transitions in climate type, a comparison of downscaling
methods, and an associated assessment of the range in rainfall projection uncertainties.
Observed distribution of climate types and
changes over the last 80 years
The Australia-wide distribution of Köppen-Geiger climate types is shown in Figure 1, along
with the key climate charateristics that were used for climate-type identification. The climatetype map was generated based on the Köppen-Geiger climate classification method, as
described in Peel et al. (2007) for historical climate conditions during the period 1930 to 2010.
Summary statistics of those charateristics are also given in Table 1. Climate types are closely
linked to rainfall distribution, intensity and seasonality across the continent. The northern
regions (under climate type Aw; see Table 1) are greatly influenced by monsoons and tropical
cyclones, both of which bring heavy rains during summer months. Rainfall in the south-west
(Csa/Csb climate types) is dominated by heavy-rain events occurring during winter. In the
south and south-east, frontal weather systems and east coast lows during winter, in
combination with localised troughs, bring occasional heavy rains with prolonged periods of
lower-intensity rainfall, mainly during winter. The subtropical ridge brings dry and stable
conditions to large parts of middle Australia. To some extent, the approximate position of the
ridge separates the summer-dominated rainfall in the north from the winter-dominated rainfall
in the south. The southern regions also experience an overall cooler climate.
o
Over the last 80 years there has been an overall increase in temperature of up to 0.6 C and
regional changes in rainfall have varied across the country (Nicholls 2006). Changes in
climate-types distributions are a result of climate trends presented in maps of mean trends in
precipitation and temperature over Australia in Figure 2(a) and Figure 2(b) for the 1930–2010
period. These precipitation and temperature trends are similar to those published by the
Bureau of Meteorology on its website www.bom.gov.au/cgi-bin/climate/change/trendmaps.cgi.
As a result of such changes in temperature and rainfall, the extent of the areas under various
climate types has undergone certain changes. Overall, for a 1930–2010 baseline, 76.6 per
cent of Australia is classified as arid, 13.9 per cent as temperate and 9.5 per cent as tropical
(Barron et al. 2010). The maps of climate types for the periods 1930–1960, 1940–1970,
1950–1980, 1960–1990, 1970–2000, and 1980–2010 (shown in Figure 3) quantify historical
changes in the distribution of climate types; these changes are also expressed as time-series
of the percentage of areal coverage over Australia for each climate type (Figure 4).
The largest 1930–2010 observed transition in climate types has been from hot desert (BWh
climate type) to hot steppe (BSh climate type) conditions. The transition from desert
conditions to steppe conditions in central and northern Australia was due to increased mean
annual precipitation, causing a southward shift in the BSh climate type in central-northern
Australia and in the Aw climate type in the north (Figure 3). Drier summers in south-western
Victoria resulted in the transition from Cfb to the Csb climate type. A decline in the occurrence
NATIONAL WATER COMMISSION — WATERLINES
9
of the Csa climate type is noticeable in the drying south-western part of Western Australia
(Figure 3).
Table 1: Characteristics of selected climate zones
Climate types
Rainfall
Rainfall seasonality:
summer rainfall as
proportion of annual
Mean temperature
Annual
(mm)
Range
(mm)
Annual
Range
Annual
(ºC)
Range (ºC)
Combined
climate
types
Tropical
savannah
Aw
1125
758–2038
0.92
0.67–0.96
26.7
22.3–29.5
Tropic (1)
Arid desert hot
BWh
254
138–417
0.67
0.26–0.88
22.5
18.0–28.2
Arid (2)
Arid steppe hot
BSh
483
225–870
0.75
0.15–0.96
23.4
18.0–29.7
Arid steppe cold
BSk
342
235–498
0.44
0.26–0.69
16.9
14.2–18.0
Temperate
without dry
season with hot
summer
Cfa
762
439–3493
0.63
0.37–0.79
18.6
14.1–23.4
Winter
rainfall (5)
Temperate
without dry
season with
warm summer
Cfb
953
433–3219
0.49
0.33–0.72
12.8
6.7–18.5
Equi­
seasonal–
warm (4)
Temperate with
dry hot summer
Csa
557
341–1517
0.22
0.15–0.77
17.5
14.8–21.5
Temperate with
dry warm
summer
Csb
665
347–1200
0.30
0.15–0.40
15.0
9.3–17.3
Equi­
seasonal–
hot (3)
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Figure 1: Current climate parameters: a) Köppen-Geiger climate zones; b) mean annual
temperature; c) mean annual precipitation; d) proportion of summer precipitation
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Figure 2: Observed historical 1930–2010 trends: a) gridded precipitation (mm/yr) and b)
o
temperature ( C/yr)
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Figure 3: Historical series of Australian Köppen-Geiger climate type maps derived for 1930–
1960, 1940–1970, 1950–1980, 1960–1990, 1970–2000 and 1980–2010
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Figure 4: Changes in the areas (as percentage of Australia land) with observed climate types
for time periods shown in Figure 3 plotted against the end year of the considered periods
Projections of future climate change and the
effect on extent of Köppen-Geiger climate types
occurrence
There is broad scientific consensus that increases in greenhouse gas emissions are causing
increases in global mean temperature. This global warming can lead to a change in climate
that affects regional weather in various ways, including increased climate variability (IPCC
2007).
This project scales observed series of gridded climate data according to three global warming
scenarios for two future periods. The global warming scenarios (relative to ~1990) used were:

for 2030: high (1.3°C), medium (1.0°C) and low (0.7°C)

for 2050: high (2.4°C), medium (1.7°C) and low (1.0°C)
These scenarios account for the full range of projected global warming as inferred from the
IPCC AR4 (IPCC 2007) and the latest climate change projection analysis for Australia
(CSIRO and BOM 2007)Since there are significant differences in future climate projections
between GCMs,16 GCMs were used for each global warming scenario to produce a range of
potential future climate change (Crosbie et al. 2011a). The 16 GCMs (Table 2) encompass
those from the IPCC AR4 (IPCC 2007) that provided the daily rainfall data required to
construct future projections of changes in rainfall by the daily scaling method, explained
below.
A technique based on ‘pattern scaling’ was then applied to perturb the observed historical
daily sequences on a 5 km grid to generate plausible future climate sequences, used as
inputs in modelling future recharge projections. The technique is termed ‘daily scaling’
(outlined in Chiew et al. 2008; and Chiew et al. 2009) and takes into account different relative
changes of different percentiles of rainfall, i.e. if intense rainfalls change more in the GCM
projections this is reflected in the scaling factors for the higher percentile rainfalls (Mpelasoka
and Chiew 2009). Other sequences of daily climate variables are scaled according to
projected seasonal changes.
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Plausible rainfall changes for 2030 and 2050 comprised 48 future climate variants (three
global warming scenarios x 16 GCMs) on a 0.05° x 0.05° grid across Australia. These are
presented for the medium global warming scenario in Figure 5 and Figure 6, for 2030 and
2050 respectively.
Table 2: Global climate models used in this study
Organisation
Country
CMIP3 I.D.
Abbreviation
Bjerknes Centre for Climate Research
Norway
BCCR–BCM2.0
BCCR
Canadian Centre for Climate Modelling & Analysis
Canada
CGCM3.1(T63)
CCCMA
Météo-France/Centre National de Recherches
Météorologiques
France
CNRM–CM3
CNRM
CSIRO Atmospheric Research
Australia
CSIRO–Mk3.0
CSIRO MK3.0
CSIRO Atmospheric Research
Australia
CSIRO–Mk3.5
CSIRO MK3.5
Max Planck Institute for Meteorology
Germany
ECHAM5/ MPI–OM
MPI
Meteorological Institute of the University of Bonn,
Meteorological Research Institute of KMA, and
Model and Data group.
Germany/Korea
ECHO–G
MIUB
US Dept. of Commerce/NOAA/Geophysical Fluid
Dynamics Laboratory
US
GFDL–CM2.0
GFDL CM2.0
US Dept. of Commerce/NOAA/Geophysical Fluid
Dynamics Laboratory
US
GFDL–CM2.1
GFDL CM2.1
NASA/Goddard Institute for Space Studies
US
GISS-ER
GISS
Instituto Nazionale di Geofisica e Vulcanologia
Italy
INGV–SXG
INGV
Institute for Numerical Mathematics
Russia
INM–CM3.0
INMCM
Institut Pierre Simon Laplace*
France
IPSL–CM4
IPSL
Center for Climate System Research (The
University of Tokyo), National Institute for
Environmental Studies, and Frontier Research
Center for Global Change (JAMSTEC)
Japan
MIROC3.2(medres)
MIROC
Japan
MRI–CGCM2.3.2
MRI
US
PCM
NCAR
US
CCSM-3.0
CCSM
Meteorological Research Institute
*
National Center for Atmospheric Research
National Center for Atmospheric Research
#
UK Meteorological Office / Hadley Centre
#
UK
UKMO–HadCM3
HadCM3
UK Meteorological Office / Hadley Centre
#
UK
UKMO–HadGEM1
HadGEM1
* Not used in climate-types analysis.
# Not used in pattern scaling analysis (due to unavailability of daily data).
NATIONAL WATER COMMISSION — WATERLINES
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Figure 5: Percentage change in annual average rainfall projected from each GCM for a future
climate (~2030) relative to the historical climate under a medium global warming scenario
(+1.0°C)
Figure 5 and Figure 6 highlight that for most regions of Australia there is a large range in
projected rainfall changes across the 16 GCMs and thus little agreement among GCMs.
Notable exceptions are south-west Western Australia and the southern MDB, where all GCMs
project a decrease in rainfall for these areas. For each future period, from the 48 projections,
a wet, a median and a dry future climate have been selected using a GCM-weighting method
(using the same approach as one for diffuse recharge-scaling factor (RSF) assessment as
discussed in Chapter 4) and expressed as a precipitation (rainfall) scaling factor (PSF). These
three summaries emphasise the central tendency (median) and range (dry and wet
representing 10th and 90th percentiles) across the 16 GCMs (Figure 7). The other climate
variables used as inputs to recharge modelling were also scaled using the ‘pattern scaling’
approach (i.e. temperature, relative humidity, and solar radiation (see Appendix 1, Figure 63
to Figure 65).
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Figure 6: As in Figure 5, but for a ~2050 medium global warming scenario (+1.7°C)
NATIONAL WATER COMMISSION — WATERLINES
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Figure 7: Precipitation scaling factors (PSF): change in annual average rainfall projected for
wet, median and dry future climate scenarios for 2030 (top row) and 2050 (bottom row)
relative to baseline
The GCM-projected changes in temperature and rainfall under future climate scenarios are
likely to produce changes in the distribution of climate types across Australia. In turn these
may cause changes in vegetation cover or limitations to viable land use, which produce an
additional impact on water resources.
Projected Australian Köppen-Geiger climate-type maps were derived for these 2030 and 2050
low, medium and high global warming projections (given the Köppen-Geiger classification
requirement for monthly data, as opposed to daily data as discussed above, a slightly
different set of GCMs were used as outlined in Table 2). The projected climate-type maps
were summarised to produce: a mode climate-type map; a comparison between the baseline
climate type and the projected mode climate type; a frequency map of the mode climate type;
a comparison between the baseline climate type and the projected mode climate type; and a
count of the number of climate types projected. Results for the 2050 medium global warming
projection are shown in Figure 8 (the results for 2030 can be found in Barron et al. 2010). The
mode climate type map classifies each pixel according to the most frequent climate type
produced across the 17 GCMs used. The baseline comparison map shows where this
projected type has changed from that of the historical baseline. The frequency map of this
mode climate type shows how many of the 17 GCMs project the mode climate type, i.e. how
consistent the projections are. The count of the number of climate types map, as another
measure of consistency, shows how many different climate types where projected across the
17 GCMs.
NATIONAL WATER COMMISSION — WATERLINES
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Figure 8: 2050 medium global warming projections: a) mode climate type; b) frequency of the
mode climate type; 0—no difference, 1—different; c) mode climate type compared to baseline
climate type; d) number of different projected climate types
Focusing on the 2050 medium global warming projection results, the largest transitions in
climate type are: BSh to BWh, BSk to BSh, and Cfa to BSh. These transitions can be
attributed to a general projected increase in temperature, a projected increase in rainfall in
most parts of far northern Australia, and a projected decline in rainfall in most southern and
coastal areas. Inconsistencies in the projected climate types arise from the GCM projection
range, particularly in rainfall. The temperature projections tend to be less consistent in north­
west Western Australia, southern Queensland, northern New South Wales, and southern
South Australia. The rainfall projections tend to be less consistent in coastal areas,
particularly Tasmania, and the north, east, and south-west coasts of mainland Australia.
Figure 9 shows that, as a function of global warming, the area of BWh (and to a lesser extent
BSh and Aw) will increase, while the area of BSk, Cfb, Cfa, Csb, Cwa, and BWk are projected
to decrease.
The geographical shifts in climate type (Figure 8) could potentially influence land-cover
change. When the current BRS (2008) land cover is overlain with shading to indicate
projected climate type transition zones (Figure 10(a) and Figure 10(b), for 2030 and 2050
medium global warming projections, respectively), it is evident that the projected
NATIONAL WATER COMMISSION — WATERLINES
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encroachment of the hot, arid desert-climate type (BWh) further south into the northern parts
of the south-eastern cropping zones could lead to changes from annual crops to native
shrublands which could subsequently cause a reduction in recharge.
Figure 9: Areal percentage of projected climate types over Australia against degrees of global
warming
Figure 10: Current land cover overlain with mode projected climate type transition zones for
the a) 2030 and b) 2050 medium global warming projections
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Variability and uncertainty in climate projections
from different downscaling approaches
The daily scaling technique described above was the only method readily applicable at the
national scale because of data requirements and computational limitations, with the resulting
projections used for nationwide recharge estimation in Chapter 4. To compare daily scaling
projections with other downscaling methods, a limited comparison of three downscaling
methods was undertaken. The methods were: 1) daily scaling, as used above (daily); 2)
stochastic downscaling (ST); and 3) daily scaling using dynamical downscaling model Cubic
Conformal Atmospheric Model (CCAM) results (CCAM-scaled). Details of the downscaling
methods are presented in Barron et al. (2010). Five GCMs (CSIRO Mk3.5, GFDL 2.0, GFDL
2.1, MIROC 3.2 midres, and MPI-ECHAM5) were used to drive these three downscaling
methods. The methods were applied using a common baseline period (observed data) of
1981–2000 and a projection period of 2046–2065 (IPCC A2 scenario) for three study sites
chosen for their contrasting hydrological regimes. The Wanneroo site is on the Swan Coastal
Plain in Western Australia and has high rainfall and high recharge (Sharma et al. 1991). The
Moorook site is in the Riverland in South Australia and has low rainfall and low recharge
(Cook et al. 2004). The Livingston Creek site is in the Murrumbidgee catchment in New South
Wales and has medium rainfall and low recharge; it is the only one of the three sites to have
any runoff (Summerell 2004).
Results are summarised as boxplots that show the range in uncertainty of projected rainfall
changes due to GCMs and downscaling techniques. A full set of results and discussion are
presented in Barron et al. (2010) and Crosbie et al. (2011b). The downscaled results at each
location produced a wide range of projected rainfall changes, predominantly due to the large
range in daily scaled results (Figure 11). Across the five GCMs and three downscaling
techniques at Gnangara, the 2046–2065 future rainfall projection changes (relative to 1981–
2000) ranged from a minimum of –32 per cent to a maximum of +7 per cent with a median of
–18 per cent. At Moorook the future rainfall projections ranged from –35 per cent to +18 per
cent with a median of –11 per cent. At Livingstone Creek the future rainfall projections ranged
from –32 per cent to +8 per cent with a median of –13 per cent. The GFDL 2.0 GCM projected
the lowest median future rainfall at each site. The highest median future rainfall was projected
by a different GCM at each site. The stochastic downscaling gave the lowest median rainfall
change at each site and CCAM-scaled gave the highest median rainfall change at two sites.
The daily scaling gave the greatest range between maximum and minimum rainfall
projections at all three sites. From these results it is clear that relying on a single GCM and
downscaling method could severely misrepresent the range of uncertainties in rainfall and
recharge projections (see Crosbie et al. 2011b for recharge comparison). However, the
results for daily downscaling produce a wider range of projected rainfall changes and, as
such, cover the projected rainfall changes derived from the other downscaling methods.
NATIONAL WATER COMMISSION — WATERLINES
21
20
20
Moorook
Gnangara
-10
-20
0
-10
-20
-30
-40
-40
-40
CS
IR
EC O
HA
M
G
FD
L2
0
G
FD
L2
M 1
IR
O
C
-30
CS
IR
EC O
HA
M
G
FD
L2
0
G
FD
L2
M 1
IR
O
C
-30
20
20
Gnangara
Livingston Ck
Moorook
-20
-10
-20
0
-10
-20
ST
Y
IL
DA
IL
DA
CC
AM
-40
ST
-30
-40
Y
-30
-40
CC
AM
-30
Y
-10
0
IL
0
10
Rainfall (%)
10
Rainfall (%)
10
DA
-20
0
CC
AM
-10
10
Rainfall (%)
Rainfall (%)
0
20
Rainfall (%)
Livingston Ck
10
CS
IR
EC O
HA
M
G
FD
L2
0
G
FD
L2
M 1
IR
O
C
Rainfall (%)
10
ST
20
Figure 11: Boxplots of the change in rainfall projected at three sites for the IPCC A2 scenario
comparing differences in GCMs and downscaling methods (note: there are only three points
in the box for the top row of plots and five points in the bottom row)
In addition to the changes in rainfall totals, a change in the temporal sequencing of rainfall
events also potentially influences recharge. Barron et al. (2010) determined that, after rainfall
intensity, prolonged periods of rain had the most impact on recharge. Analysis of changes in
event-based statistics has not been undertaken as two of the approaches used (daily and
CCAM-scaled) only modify the magnitudes but not the sequencing of events. However, the
stochastic downscaling method can produce changes in sequencing. For example, Fu and
Charles (Fu and Charles 2011 accepted) analysed stochastically downscaled projections for
south-eastern Australia using the same method. They determined that, as well as changes to
mean rainfall and intensity, there were also projected increases in the number of dry days and
length of runs of consecutive dry days and, correspondingly, decreases in the number of wet
days and length of runs of consecutive wet days. They concluded that the combined effect of
these changes would be to further reduce runoff in addition to that which could be expected
due to the mean changes alone. Such changes could also be expected to influence recharge.
Episodic recharge would also be influenced by changes to the frequencies and extent of
longer-term events such as droughts. Up to 20 per cent more droughts (defined as the one-in­
10 year soil moisture deficit from 1974 to 2003) have been projected over most of Australia by
2030, and up to 80 per cent more by 2070 in south-western Australia (Mpelasoka et al. 2008).
Increases in the Palmer Drought Severity Index for the IPCC SRES A2 scenario are projected
over much of eastern Australia (Burke et al. 2006).
Overall, the comparison of rainfall projection uncertainty from multiple GCMs and downscaling
methods (Figure 11) highlights the need to assess projection uncertainty when applying
recharge modelling to the whole of Australia (Crosbie et al. 2011a; and Chapter 4). Given it
was not possible to extend the stochastic downscaling or dynamical downscaling to
continental scales within the project timelines, a pragmatic decision was taken to apply the
daily scaling approach to as many GCMs as possible (the 16 GCMs in) for the low, medium
and high scenarios (as discussed above) in order to encompass as much projection
uncertainty as possible.
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Conclusions Observed time series of temperature and rainfall over Australia indicate a warming trend over
most of the country (except for the inland north-west), increasing rainfall over northern, central
and north-west Australia, and decreasing rainfall in eastern, south-east and south-west
Australia (Figure 2).
The trends in temperature and rainfall have resulted in substantial decadal changes in spatial
distribution of the main Köppen-Geiger climate types found across Australia (Figure 3 and
Figure 4). There has been a southerly extension of the tropical types in the far north together
with a contraction in the northern extent of arid types. The arid types have expanded to the
south and south-east, with corresponding contraction of temperate types. These changes
indicate a possible contraction to the northern extent of the southern cropping zones.
Projected changes in the spatial distribution of climate types indicate an increase in aridity at
the expense of temperate coverage (Figure 8 and Figure 9). The southern Australia
projections are more consistent with observed trends than are those for northern Australia. As
the projected warming and southern Australian rainfall decline accelerates between 2030 and
2050, there is increased likelihood of land-cover change from annnual cropping to native
shrublands and grasslands in southern Australia (Figure 10).
The uncertainties in direction and magnitude of regional rainfall changes are pervasive and
limit our ability to provide confident assessments of likely impacts for many regions of
Australia (Figure 5). Projections are more consistent for south-west Western Australia and the
southern MDB where all GCMs project a decrease in rainfall.
The large uncertainties in the projected changes in Köppen-Geiger climate types over
Australia mainly emanate from the large range of rainfall changes projected by GCMs. In
addition, a site- specific comparison showed that there can also be large uncertainties
associated with different downscaling methods (Figure 11).
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23
2. Aquifer characterisation and
prioritisation
The effect of climate change on groundwater resources can be influenced by the
hydrogeological setting of the aquifer, and one of the project objectives was to characterise
the sensitivity of Australian aquifers to possible changes in climate, irrespective of the
predictive climate modelling. This chapter summarises the approach for aquifer prioritisation
at a national scale developed within the current project and the results of the characterisation
of aquifers in terms of their sensitivity to climate change and national importance. Overall,
14 groundwater systems were identified as high-priority aquifers, which are further described
in Chapter 6 along with the other project results specific for those aquifers.
Characterising aquifer sensitivity to climate
change
Aquifers are highly variable and respond differently to perturbations in climate. Yet their
sensitivity to change can be characterised on a generic level (based on aquifer type) and by
examining the nature of their recharge and discharge processes.
Broad aquifer types typical for Australia have been defined for the purposes of this project
and are listed in Table 3. Several types of alluvial aquifer are distinguished according to their
position in the landscape. Each aquifer has generic sensitivities in relation to changes in
climate. It is apparent that some aquifer types will be more sensitive to changes in climate
than others; particularly those with limited storage relative to recharge.
Climate change is likely to have the most immediate effect on recharge and discharge
processes. Understanding these processes and their sensitivity to climate change highlights
the potential pressure points and vulnerabilities of an aquifer. Additionally, climate change
may also lead to greater groundwater extraction rates. Aquifers with a high proportion of
groundwater usage and those which coincide with highly developed surface water resources
(such that there is little additional capacity) are likely to be most sensitive.
This project has undertaken the characterisation of aquifers in two phases. First, generic
aquifer sensitivity to climate change and aquifer importance has been analysed for all
Australian aquifers as part of the aquifer prioritisation activities (discussed in this chapter).
Second, the recharge and discharge processes of priority aquifers have been examined to
highlight the potential pressure points and vulnerabilities of these aquifers to climate change
(discussed in Chapter 6).
Aquifer prioritisation
Prioritisation factors
The prioritisation scheme ranks aquifers by sensitivity and importance separately, and then
combines these indices. Its objective is to define priority aquifers—those which are sensitive
and important.
A score for sensitivity has been devised to represent the generic sensitivity of an aquifer. It is
calculated by multiplying two metrics: the level of development within an aquifer; and a metric
for aquifer responsiveness that is defined by likely recharge to storage ratios.
NATIONAL WATER COMMISSION — WATERLINES
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The level of development within an aquifer is calculated as follows:
[1]
where E is the current level of extraction (ML/year) and SY is the reported sustainable yield of
the aquifer (ML/year). Inclusion of the metric is based on the assumption that a high level of
development may correspond to a greater degree of sensitivity—there is likely to be reduced
capacity to buffer against changes in the water balance.
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Table 3: Aquifer types and their general sensitivity to changes in climate
Aquifer type
Definition
Examples
Likely sensitivities to climate
change
Basalts
Aquifers hosted in basalt
Toowoomba
Basalts (Qld),
Tertiary Basalts
(Tas.)
Often have highly permeable
soils, limited storage relative to
recharge and short flow paths
from recharge to discharge
zones.
Basalts differ from other
fractured-rock aquifers in that
groundwater may be contained in
porous zones (associated with
gas bubbles that formed when
lava cooled) as well as in
fractures.
Carbonate/karstic
Aquifers hosted in karstic
geologies.
Daly Basin (NT)
Karstic features can act as
preferential flow paths leading to
rapid recharge and discharge.
Coastal sands
Shallow coastal
sedimentary aquifers with
ocean discharge.
Albany (WA)
Limited storage and potential for
salt water intrusion.
Fractured rock
Aquifers hosted in fractures
and fissures in geology of
otherwise low permeability.
Adelaide
Geosyncline
(SA)
Limited storage relative to
recharge and short flow paths.
Sedimentary basins Aquifers hosted in thick,
Perth Basin
Not especially sensitive given
sedimentary sequences that (WA), GAB (Qld, high level of groundwater storage
are often confined.
NT, NSW, SA)
relative to recharge.
Alluvial aquifers
Upper valley
alluvium
Shallow and narrow alluvial
aquifers in incised, upland
valley systems. Receive a
high proportion of localised
recharge, from streams.
Belubula (NSW), High degree of surface water–
Upper Ovens
groundwater connectivity
(Vic.)
sensitive to climatic changes.
Limited storage, short flow paths
from recharge to discharge
zones.
Alluvium
Alluvial aquifers of
Midmoderate thickness and
Murrumbidgee
extent, in undulating terrain. (NSW)
Receive a high proportion of
localised recharge, from
streams.
High degree of surface water–
groundwater connectivity and
overbank (flood) recharge can be
significant recharge mechanism
and these processes sensitive to
climate change.
Riverine plains
Broad, thick alluvial aquifers Calivil (NSW,
with widespread floodplains. Vic.)
Aquifers associated with
prehistoric alluvial
sequences and often
semiconfined. Receive a
high proportion of localised
recharge, from streams.
Not especially sensitive given
high level of groundwater storage
relative to recharge.
Alluvial aquifers with
connection to coast and/or
estuaries.
Surface water–groundwater
connectivity sensitive to climate
changes.
Coastal alluvium
Gascoyne River
(WA)
Typically low diffuse recharge
due to low soil permeability and
location in drier climate zones.
Potential for salt water intrusion.
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Aquifer responsiveness to change in the water balance is linked to the likely recharge (R) to
storage (S) ratios. A high level of recharge relative to storage is suggestive of a greater
sensitivity as there will be minimal buffering capacity (i.e. storage) if recharge rates are
perturbed by climate change. Because there is significant uncertainty in deriving both
recharge and storage for all aquifers across Australia, a rating function is introduced whereby:
[2]
Aquifers are assigned ratings of high, moderate and low responsiveness according to their
generic aquifer type (Table 3) and the climate zone where they are located. The development
of the rating system was informed by an analysis of recharge and storage terms in the MDB
as reported in Currie et al. (2010). Note that since Currie et al. (2010), the value assigned to a
low responsiveness rating has been revised down to 0.01 (from 0.1) as the previous value
overestimated the sensitivity of these aquifer types, particularly for large sedimentary basins
like the GAB.
The level of development [1] and aquifer responsiveness [2] metrics are multiplied to calculate
the overall sensitivity of an aquifer as follows:
[3]
In addition to aquifer sensitivity, an index has been devised to measure aquifer importance—
i.e. the importance of the aquifer for consumptive users and the environment. It is represented
as a function of the current level of extraction, the volume of the resource and the presence of
groundwater-dependent ecosystems (GDEs). The index for aquifer importance is shown as
follows:
[4]
where I is aquifer importance, E is the current level of extraction (ML/year), Emax is the highest
level of extraction in the dataset, SY is the sustainable yield (ML/year). and SY max is the
highest sustainable yield in the dataset. E/Emax is termed the ‘extraction metric’ and SY/SYmax
is termed the ‘size of resource’ metric. The presence of GDEs in the aquifer is represented as
separate functions for river baseflow GDEs and other GDE types (wetland or terrestrial
vegetation GDEs), which are listed separately in the AWR 2005 dataset (AWR 2005). The
rationale for treating river baseflow GDEs separately to other GDEs was to allow for
environmental baseflow as a particular factor of aquifer importance. The GDE functions are
both defined numerically as follows:
[5]
where 0.85 and 0.15 are weighting factors arbitrarily selected to define the presence or
absence of GDEs. The sensitivity of the results to the choice of these weighting factors is
analysed in Currie et al. (2010).
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Aquifer definition and data sources
Groundwater management units (GMUs) are areas where a groundwater resource (or parts
thereof) is designated for management by a jurisdictional water agency. While the extent of a
given GMU is sometimes based on social rather than physical boundaries, GMUs are often
associated with geological units or aquifers. The approach for this project was to undertake
the analysis at the aquifer level and, as GMUs are defined for parts of larger aquifers, they
have been used to represent the major aquifers of Australia—either individually (where a
GMU accurately represented an entire aquifer) or by aggregating several GMUs to represent
a larger regional aquifer (where the aquifer was represented by more than one GMU). See
Currie et al. (2010) for a listing of which GMUs were selected to represent an aquifer.
The broad regional aquifers form the assessment unit for the prioritisation scheme. Where
multiple-layered aquifers occur at one location—e.g. a large sedimentary basin such as the
Perth Basin—the GMUs have been combined to represent one aquifer system as opposed to
multiple aquifers. Where a number of smaller yet similar aquifers occur at separate locations
within the same region (e.g. coastal sands along the east coast), these have been grouped
into the one assessment unit. Aquifer systems have also been further subdivided by climate
1
zone .
The resulting map of broad regional aquifers is shown in Figure 12. In places, the aquifer
boundaries may not align with the actual physical setting of aquifers—they are a coarse
representation of aquifers as defined by management boundaries. The management
boundaries are the basis upon which groundwater data and statistics are collated for
prioritisation purposes. The coverage is yet to be reviewed by jurisdictional representatives
and might require adjustment for future use.
1
Climate zone classification is based on grouping Koppen-Geiger codes as follows: 1) Tropical = Af, Am, Aw; 2) Arid/SemiArid = BWh, BWk, BSh, BSk; 3) Mediterranean = Csa, Csb; 4) Humid subtropical = Cwa, Cfa; 5) Temperate = Cfb, Cfc,
Dfb, Dfc. The Koppen-Geiger zones were delineated according to an historical climate: BAWAP data from 1970–2009. See
also Chapter 2.
NATIONAL WATER COMMISSION — WATERLINES
28
Figure 12: Major aquifer systems of Australia—assessment units for the prioritisation scheme
The base data required to populate the prioritisation index for each aquifer are: current
groundwater extraction (use), sustainable yield and the presence (or absence) of GDEs.
Much of this data is listed in Australian water resources 2005 (AWR, 2005). The AWR 2005
data was updated by the most recent estimates of extraction and sustainable yield volumes,
which were either obtained from sustainable-yield studies in relevant areas or sought from
each jurisdiction. Where sustainable-yield volumes were not available, groundwater
allocations were used as a sustainable-yield surrogate. This assumption is consistent with
NWI objectives that allocations should reflect sustainable yields. In addition to extraction and
sustainable-yield data, the AWR 2005 dataset lists whether GDEs have been identified for
each GMU. GDEs are listed according to type, which allowed for the breakdown of GDEs into
river baseflow, wetland and terrestrial GDEs.
While up-to-date information has been obtained, there are various limitations associated with
the data used to populate the prioritisation scheme. Extraction rates can vary significantly
from year to year. The sustainable yield estimates vary in quality as they are subject to
different definitions and interpretations across different jurisdictions and regions. GDE data is
limited to existing data (AWR 2005), which is poorly documented in terms of how GDEs were
identified, their level of groundwater dependence (relative to the regional aquifer), how
significant they are in a national context, and their susceptibility to perturbations in the water
balance. It is also possible that the dataset may not include several important GDEs. The
outputs from the NWC GDE Atlas project may be useful for further improvement in this
prioritisation framework.
NATIONAL WATER COMMISSION — WATERLINES
29
Prioritisation results
The results obtained for the six individual metrics that comprise the prioritisation scheme are
shown in Figure 13. The first four maps (a to d) relate to the measure of aquifer importance.
The last two maps (e and f) relate to the measure of aquifer sensitivity. The results of the
analysis are provided in Currie et al. (2010) in some detail.
Aquifers have been ranked according to their prioritisation scores for sensitivity and
importance. The top 20 aquifers from each category define the aquifers that are most
sensitive and those that are most important. An overall priority grouping was defined as the
aquifers that are both sensitive and important.
An ordination procedure was used to define the priority grouping. Aquifers are ordered in
terms of their sensitivity score and assigned a rank number accordingly—where 1 denotes the
highest score, 2 the next highest score, and so on. An identical approach has been taken to
define an importance rank. The sensitivity rank is plotted against the importance rank (Figure
14). There is a relatively even scattering of points and there is no relationship between the
two ranks. Aquifers that fall close to the origin (i.e. are high ranking in terms of sensitivity and
importance) are considered to be priority aquifers (both important and sensitive). The group of
aquifers that rank in the top 20 has been identified for sensitivity and for importance. These
aquifers are termed either sensitive aquifers (of low importance rating) or important aquifers
(of low sensitivity rating).
NATIONAL WATER COMMISSION — WATERLINES
30
Figure 13: Aquifer prioritisation results for individual metrics: a) E/Emax; b) SY/SYmax; c)
f(baseflow GDEs); d) f(other GDE types); e) E/SY; f) aquifer responsiveness for f(R:S)
NATIONAL WATER COMMISSION — WATERLINES
31
120
Sensitivity rank
100
80
60
40
20
0
0
20
40
60
80
100
120
Importance rank
Figure 14: Plot of aquifer sensitivity rank versus importance rank. Orange shading indicates
selection of priority aquifers, green shading indicates selection of sensitive aquifers (of low
importance rating), blue shading indicates selection of important aquifers (of low sensitivity
rating).
The results of the prioritisation process are summarised in Table 4, which lists the three
priority groupings (for the names of an individual aquifers fall in each regional aquifer, see
Appendix 2). The location of these aquifers is shown in Figure 15. Of the 20 most sensitive
aquifers (column 1 in
NATIONAL WATER COMMISSION — WATERLINES
32
Table 4), there are seven alluvial aquifers (three alluvium, two coastal alluvium and two
upper-valley alluvium), five fractured-rock aquifers, three basalt aquifers, three coastal sand
aquifers and two carbonate/karstic aquifers. Probably owing to the definition of the aquifer
responsiveness index, there are no sedimentary-basin aquifers or riverine plains aquifers
present. Similarly, no aquifers from the arid/semi-arid climate zone are deemed sensitive.
The 20 most important aquifers (column 2 in Table 14) comprised aquifers of different types,
with the exception of basalts and upper-valley alluvium. There are no aquifers from the
tropical climate zone.
The 14 priority aquifers comprise all aquifer types with the exception of sedimentary basins,
riverine plains and upper-valley alluvial aquifers. All climate zones are represented.
The plot similar to Figure 14 but showing the aquifer type and climate zone of aquifer
occurrence is reproduced in Figure 16. A close examination of this figure indicates that
fractured rock, alluvium and coastal aquifers show on average higher sensitivity to climate
change. Sedimentary basins tend to be rated as important—most probably due to the large
size of these resources in terms of current extraction rates and sustainable yields. The noted
trends from Figure 16 are summarised in Table 5.
NATIONAL WATER COMMISSION — WATERLINES
33
Newer Volcanics
19, 17
24, 16
Upper
Condamine and
Border Rivers
Alluvium
33, 18
Atherton
Tablelands
35, 8
Coastal River
Alluvium 1
36, 15
Toowoomba
Basalts
45, 3
TLA 3
20 most important
aquifers listed in
order of
decreasing
sensitivity
Importance,
sensitivity
rank
Lachlan
19, 17
Gunnedah
7, 25
Pilbara
10, 29
Port Campbell
Limestone
17, 36
Coastal River
Alluvium 4
4, 38
Coastal Sands 4
6, 39
62, 20
Otway Basin
2, 49
Unincorporated
Area GMW
63, 19
Lachlan Fold Belt 5
15, 52
Eyre Peninsula
Limestone
Lenses
68, 13
New England Fold
Belt 4
18, 56
Fractured Rock
Aquifer 4
75, 9
GAB 2
3, 60
Upper Valley
Alluvium 4
83, 1
Lachlan Fold Belt 2
14, 63
Fractured Rock
Aquifer 1
85, 9
GAB 4
8, 64
Humevale
Siltstone
86, 12
Fractured and
weathered rock 2
11, 70
Fractured rock
87, 5
Calivil
1, 72
Quaternary sand
dune deposits
89, 2
Murray Group
12, 77
Quaternary
Alluvium
associated with
the Goulburn
River
90, 14
South Perth Basin
9, 79
Coastal River
Alluvium 5
93, 6
Central Perth Basin
5, 82
Albany
97, 4
Goldfields
13, 94
Upper-Valley
Alluvium 5
107, 7
North Perth Basin
16, 96
Ord–Victoria 1
113, 11
Canning
20, 99
Important aquifers (of low sensitivity rating)
Sensitive aquifers (of low importance rating)
Priority aquifers: sensitive and important
Lachlan
Importance,
sensitivity
rank
Priority aquifers: sensitive and important
20 most
sensitive
aquifers listed
in order of
decreasing
importance
Priority aquifers:
sensitive and
important
Table 4: Prioritisation results—sensitive, important and priority aquifers* (showing in the
colours as in Figure 15)
Aquifers with
both
moderately
high
sensitivity
and
importance
Importance,
sensitivity
ranks
Adelaide
Geosyncline 3
27, 30
Daly Basin
30, 35
*Individual aquifer names are given in Appendix 2
NATIONAL WATER COMMISSION — WATERLINES
34
Figure 15: Map showing location of priority aquifers
120
2
Sensitivity Rank
4
1
5
2
2 5
5
1
3
45
3
2
4 5
4
upper valley alluvium
5
5 3
5
1
alluvium
5
4
5 5
1
4 5 3
4 3
4
riverine plains
3
3
5
3
4
sedimentary basin
2
5
2
4
2
4
5
1
coastal sands
fractured rock
5
2
3
carbonate
5
1 2
5
5
basalts
2
2
2
5
1
5
3
3
2
44
5
2
3
5
5
45
5 41
3
52
1
2
2
2
60
20
2
2
2
40
5
55
5
2
2
2
2
32
2
2
3
4
5
3
80
2
23
100
42
42
4
coastal alluvium
5
1
5
0
0
20
40
60
80
100
120
Importance Rank
Figure 16: Plot of prioritisation ranks shown by aquifer type and zone. Climate zone
classification based on grouping of Köppen-Geiger codes as follows: 1) Tropical = Af, Am,
Aw; 2) Arid/Semi-arid = BWh, BWk, BSh, BSk; 3) Mediterranean = Csa, Csb; (4) Humid
subtropical = Cwa, Cfa; (5) Temperate = Cfb, Cfc, Dfb, Dfc
NATIONAL WATER COMMISSION — WATERLINES
35
Table 5: Trends noted in Figure 16
Aquifer type
Trends
Basalts
Tend to more sensitive with even importance
distribution.
Carbonate/karstic
Even distribution.
Coastal sands
Tend to be sensitive and of low importance rating,
with the exception of one priority aquifer (Coastal
Sands 4) that is listed in the top 20 for importance.
Fractured rock
Tend to more sensitive with even importance
distribution.
Sedimentary
basins
Tend to be important but not sensitive.
Alluvial aquifers
Upper valley
alluvium
Only two examples, yet shown to be very sensitive
but not important.
Alluvium
Shown to be either sensitive or less sensitive, with
no intermediate sensitivity scores.
Riverine plains
Tend to be not especially sensitive.
Coastal alluvium
Tend to be sensitive with an even importance
spread.
Notable exclusions
The prioritisation scheme has identified 14 priority aquifers, yet some significant groundwater
resources fall outside this group; instead they are listed within the sensitive aquifers (of low
importance) and important aquifers (of low sensitivity) groupings.
A number of small yet sensitive systems are listed as sensitive aquifers (of low importance).
While these are not rated as important on a national scale, they may have significant local
importance. The upper valley alluvial aquifers of New South Wales fall within this group and
include the Belubula and Cudgegong GMUs, which are both highly developed aquifers and
rated by the Murray–Darling Basin Sustainable Yields (MDBSY) project as priority GMUs
(Richardson et al. 2008). Similarly, some of the coastal sand aquifers listed are prescribed
groundwater resources and support groundwater-dependent ecosystems (e.g. Eyre Peninsula
limestone lenses and Albany).
The aquifers listed as important (of low-sensitivity rating) may also be sensitive to climate
change at a local level. These aquifers include large sedimentary basins (e.g. Perth Basin,
GAB), and riverine plains (e.g. Calivil). While the large storage volumes present in these
systems are not suggestive of high levels of sensitivity to climate change, local aspects of
these aquifers may be sensitive. For example, the superficial aquifer of the Perth Basin
supports a number of groundwater-dependent ecosystems, and the thin nature of this aquifer
suggests it will be sensitive to changes in climate. Additionally, the climate change projections
in this region are most consistent, suggesting that drying conditions are most likely.
Many of the other aquifers listed in the important (of low sensitivity) category are large
unincorporated/non-prescribed areas (e.g. Lachlan Fold Belt, New England Fold Belt,
NATIONAL WATER COMMISSION — WATERLINES
36
Goldfields). It is probable that the prioritisation scheme has overestimated their importance
due to their substantial spatial extents.
Comparision with other prioritisation studies
A concurrent prioritisation study of direct relevance has been conducted by the South
Australian Department for Water (Wood and Green 2011), where water resources (both
surface water and groundwater) were prioritised according to the potential risks posed by
climate change. The work was conducted independently of this project, yet the two share a
similar methodology in that resources were prioritised according to resource ‘significance’ and
‘sensitivity’. The major difference in the SA study was the inclusion of a climate change risk
rating based on previous climate change modelling. The results from the SA study support the
findings of this project in that the highest priority groundwater resources for South Australia
are in the Mount Lofty Ranges (Adelaide Geosyncline) and the limestone aquifers of south­
east South Australia (Otway Basin).
Priority aquifers
Table 6 lists the priority aquifers by type and climate zone, while the names of individual
aquifers included are given in Appendix 2. A broad range of aquifer type/climate zone
combinations are represented.
The priority listing includes three highly utilsed alluvial aquifer systems of the MDB associated
with mid- to upper-catchment zones. These aquifers are recharged predominantly by rivers
(both in-stream and overbank) and support intensive irrigation activities in GMUs such as the
Upper Condamine, Border Rivers, Lower Gwydir, Upper and Lower Namoi, Upper and Lower
Macquarie, Upper Lachlan, the Mid-Murrumbidgee and Upper Murray. The aquifers can be
both unconfined and semiconfined. They are most sensitive to climate change through
changes in stream flow (impacting connectivity) or indirectly via changes in extraction
behaviours.
The three priority basalt aquifers occur along the Great Dividing Range in northern and south­
eastern Queensland and in south-west Victoria. The Queensland basalt aquifers (Atherton
Tablelands and Toowoomba) are highly dynamic, characterised by high horizontal flow rates
and short groundwater-residence times. Diffuse rainfall infiltration is the primary recharge
mechanism. In the Atherton Tablelands, the groundwater system is highly connected to the
surface water drainage system and most recharge that is not extracted discharges to
streams. In the Toowoomba Basalts, discharge occurs via outflow to the Condamine Alluvium
(to which it is hydraulically connected). The groundwater resources associated with the Newer
Volcanics in Victoria are variable. Recharge occurs preferentially in areas of less-weathered
basalt, stony rises and eruption points. Groundwater flow typically radiates outward from the
elevated recharge sources into the plains. Outside of preferential recharge areas, there is a
lower flux of water reaching the watertable due to lower infiltration rates and increased
evapotranspiration, leading to higher groundwater salinities.
Of the carbonate aquifers listed, the Daly Basin is located in a monsoonal tropical climate and
will thus have quite different climate change sensitivities compared to the temperate zone of
the Otway Basin (south-eastern South Australia) and the Port Campbell Limestone
2
(southwest Victoria) . The carbonate aquifers of the Daly Basin are highly connected to the
2
In this project the Otway Basin describes only the South Australian portion of the basin, which in reality extends
across the border and includes the Port Campbell Limestone. The distinction was made to isolate the
carbonate/karstic aquifers of the broader Otway Group. In south-east South Australia, the major productive Tertiary
limestone aquifer is unconfined; whereas in Victoria, the productive Port Campbell Limestone is partly confined by
NATIONAL WATER COMMISSION — WATERLINES
37
local surface water systems, providing the primary water source for baseflows. Recharge to
the aquifers occurs via rainfall infiltration, either diffusely or directly through sink holes and
dissolution hollows (Harrington et al. 2009). The Otway Basin describes the unconfined
Tertiary limestone aquifer of south-east South Australia. The productive aquifers are quite thin
(i.e. limited available storage) and recharged predominantly by diffuse rainfall. There is
minimal natural surface drainage, with most discharge occurring via evapotranspiration,
lateral outflows, and into man-made drains. The Port Campell Limestone is an analogous
Tertiary limestone aquifer occuring on the Victoria side of the border. It differs in that it is
partially overlain by Quaternary basalts and will be confined in places.
Prioirty coastal river alluvium and coastal sand aquifers occur along the east coast between
Cooktown and Sydney in tropical and humid subtropical climate zones. The coastal river
alluvium aquifers extend inland, with groundwater hosted in coarse Quaternary foodplain
sediments. There is a high degree of surface water–groundwater connectivity. The costal
sand aquifers are relatively thin and shallow with limited storage. Recharge is via rainfall and
discharge occurs to the ocean or to estuaries. There is potential for saltwater intrusion in
these coastal aquifer systems.
The two fractured-rock aquifers listed are the Adelaide Geosyncline in South Australia
(Mediterranean climate) and the Pilbara in Western Australia (arid/semi-arid climate). The
Pilbara is nominally listed as a fractured-rock aquifer, yet also includes alluvial aquifers near
the coast. The climate is arid/semi-arid, with recharge (both rainfall and stream recharge)
occurring during sporadic, yet intense, rainfall events. The aquifers associated with the
Adelaide Geosyncline rely on more regular rainfall, which is winter dominant. Discharge
occurs to streams or as lateral outflow to connected sedimentary aquifers.
overlying basalt. The two aquifers are thus likely to exhibit a different response to climate change so they are
separated in this project.
NATIONAL WATER COMMISSION — WATERLINES
38
Table 6: Priority aquifers by aquifer type and climate zone
Aquifer
type
(1)
Tropical*
(2) Arid/
semi­
arid
(3)
Mediterranean
(4) Subtropical
Alluvium
Gunnedah
(NSW), Lachlan
(NSW), Upper
Condamine and
Border Rivers
Alluvium (Qld)
Basalts
Atherton
Tablelands (Qld),
Toowoomba
Basalts (Qld)
Carbonate/
karstic
Daly Basin
(NT)
Coastal
alluvium
Coastal
River
Alluvium
(Qld)
Newer
Volcanics
(Vic.)
Otway Basin
(SA), Port
Campbell
Limestone (Vic)
Coastal River
Alluvium (NSW &
Qld)
Coastal
sands
Fractured
rock
(5)
Temperate
Coastal Sands
(NSW & Qld)
Pilbara
(WA)
Adelaide
Geosyncline (SA)
Riverine
plains
Sedimentary
basin
Upper valley
alluvium
* Climate zone classification based on grouping of Köppen-Geiger codes as follows: 1) tropical = Af, Am,
Aw; 2) Arid/Semi-Arid = BWh, BWk, BSh, BSk; 3) Mediterranean = Csa, Csb; 4) humid subtropical =
Cwa, Cfa; (5) temperate = Cfb, Cfc, Dfb, Dfc.
Riverine plains and sedimentary basin aquifers are not listed as priority because of their low
sensitivity. And Upper Valley Alluvium aquifers are not represented as priority because of
their relatively small scale, which translates into a low importance rating on a national scale.
Limitations and recommendations for further
aquifer prioritisation
The aim of the prioritisation scheme was to provide an objective basis for selecting priority
aquifers across Australia to assess for climate change impacts. While this aim has been
achieved, some underlying assumptions and limitations need highlighting, as they affect the
results obtained.
In some cases the classification of regional aquifers was based on one large GMU that in
reality encompasses several aquifer systems. This limitation may overstate the importance of
several inland aquifers, which are primarily defined as being large resources because of their
size.
NATIONAL WATER COMMISSION — WATERLINES
39
The prioritisation scheme does not incorporate a metric for groundwater dependence—i.e. the
importance of groundwater relative to total water-use on an aquifer scale. It is reasonable to
assume that regions more dependent on groundwater would be more sensitive to climate
change than regions with similar attributes in the other prioritisation categories.
The methodology developed has been used to prioritise aquifers for the purposes of this
project. Further work would be required to implement the methodology to prioritise aquifers for
other purposes. While this work may be the first attempt to nationally prioritise aquifers by
importance, the results should not be considered as a universal ranking by importance
outside the context of this project. Any further prioritisation needs to be tightly defined
according to relevant objectives. For instance, in this project there is no value assigned to the
use of groundwater—i.e. dollar value of agricultural production or ecological value of the
GDEs present. The introduction of such metrics would significantly alter the results obtained.
Based on the analysis undertaken it is clear that the approach to further improving aquifer
prioritisation should be based on advancing knowledge in groundwater use and sustainable
yields, as well as other data that was qualitatively used within the current approach. The
following recommendations are provided to assist with such advancement:

The relative weighting of the individual metric terms used in the prioritisation scheme is
critical to the results obtained and further prioritisation activities may wish to apply a more
rigorous selection of weightings using a formalised procedure and expert guidance (e.g.
Raj and Kumar 1999). The inclusion of surface water vulnerability to climate change could
be added as a compounding factor if supported by data.

It is likely that higher-quality datasets will become available in future (e.g. GDE Atlas),
which will enhance the accuracy of further prioritisation activities.

Adjustment of boundarys or data associated with large GMUs could be used to offset
apparent bias. The introduction of a metric focused on the intensity of extraction (e.g.
extraction per unit surface area) may offset this bias.

The inclusion of a metric for groundwater dependence (i.e. the reliance on groundwater by
consumptive users) would further improve the approach.

A separate prioritisation could be developed for coastal aquifers where the threat of
seawater ingress is included.
NATIONAL WATER COMMISSION — WATERLINES
40
3. Effect of climate types and climate
change on potential groundwater
recharge
The effect of climate on renewable groundwater resources was undertaken considering
potential diffuse recharge and localised recharge associated with water losses from rivers and
floodplains to groundwater.
Discussion on diffuse recharge covers historical and future changes in recharge. It is first
focused on modelled recharge results for historical climate data for selected locations. The
analysis aims to define the effect of individual and combined climate characteristics on
potential diffuse recharge under various climate types of Australia. The chapter also provides
information on spatial variability of potential recharge under the historical climate and its
changes under projected future climate scenarios at a national scale.
Localised discharge and its changes under projected future climate scenarios are discussed
in relation to rivers and floodplains. Within the constraint of data availability, many conclusions
of this analysis are indicative and can be further improved as additional data become
available.
Diffuse groundwater recharge under the
historical climate
This section is largely based on the outcomes of an investigation of climate parameters and
climate on the potential recharge estimated using the WAVES model (Crosbie 2011a).
WAVES (Zhang and Dawes 1998) is a soil-vegetation-atmosphere-transfer (SVAT) model
that can be used to estimate the components of an unsaturated-zone water balance at a point
scale. The WAVES model requires three datasets: climate, soil and vegetation. A soil profile
of 4 m depth was modelled with a free-draining lower boundary condition. It was assumed
that the drainage through the bottom of the model (deep drainage) was potential groundwater
recharge and did not become lateral flow. The assumption was made that diffuse recharge in
dryland areas is independent of the depth of groundwater below ground surface.This
assumption results in errors where the watertable is close to the surface or where the tree
roots are deeper than 4 m.
Soil data was derived from the ASRIS v1 database (Johnston et al. 2003). The modelling was
undertaken for three vegetation classes: annuals, perennials and trees. The vegetation
parameters required by WAVES were taken from the user manual (Dawes et al. 2004). The
annuals (including crops) were modelled as annual pasture, the perennials as perennial
pasture and the trees (including forestry) as an overstorey of eucalypts with an understorey of
perennial grasses. Each climate zone used different parameters for each of the three
vegetation types modelled.
The recharge modelling was undertaken at 100 control points across Australia to reflect the
rainfall gradient. Apart from the climate data used for the modelling, the control points did not
have a physical meaning in the real world; their only role was to ensure that there were
NATIONAL WATER COMMISSION — WATERLINES
41
enough points to represent the rainfall gradient across each type and to create regression
equations between mean annual recharge and mean annual rainfall for upscaling. Their
position was also biased toward areas where groundwater is used from unconfined aquifers.
The country was split into five climate zones in which it was anticipated that the relationship
between rainfall and recharge would be similar for each combination of soil and vegetation
type. The climate types were simplified from Köppen-Geiger climate types (Barron et al. 2010)
(Figure 17):
Tropics (Af, Am, Aw, Cwa)
Arid (BWh, BWk, BSh, BSk)
Winter rainfall (Csa, Csb)
Equiseasonal–warm (Cfb, Cfb, Cfc, Dfc)
Equiseasonal–hot (Cfa).
Figure 17: Left: Köppen-Geiger climate types of Australia as defined by Peel et al. (2007)
using the climate from 1930–2009 (Barron et al. 2010). Right: Simplified climate zones used
in the modelling and the control points used for the point scale modelling
Twenty control points were used within each climate zone (Figure 17). The output of the
WAVES modelling was used to analyse the recharge relationship with historical climate
parameters (as discussed below, also in Barron et al. 2010) and to derive a national-scale
analysis of potential recharge and its changes under future climate scenarios (below, also in
Crosbie et al. 2011a).
Specifics of diffuse groundwater recharge under various
climate types
Individual climate characteristics and their combinations have profound effects on diffuse
groundwater recharge. According to the analyses undertaken here such effects have general
trends across the country but also show certain specific characteristics under individual
climate types.
NATIONAL WATER COMMISSION — WATERLINES
42
Climate types are commonly defined by a combination of rainfall and temperature and their
seasonal patterns (Chapter 2)—parameters that are also known to be dominant climate
factors influencing recharge (Chapter 1). It is useful to note that under the same climatic
conditions, recharge values may vary in orders of magnitude dependent on specific
combinations of soil type and land cover. The difference in recharge can be more than 25-fold
due to changes in land cover, i.e. vegetation, and more than 400-fold under various soils (see
Figure 66 in Appendix 3). At the same time, annual recharge percentage in rainfall can vary
from less than 1 per cent under trees and low permeability soils, to more than 50 per cent
under annuals and highly permeable soils (see Figure 67 in Appendix 3).
To allow adequate analysis of the effect of climate type on recharge, nine combinations of soil
and vegetation were selected. These included three vegetation types (annual, perennial and
trees) and three soil types with similar hydraulic properties. The soil selection was based on a
3
weighted hydraulic conductivity of approximately 0.01 m/day, 0.1 m/day and 1 m/day. As was
shown previously, the estimated recharge shows low variability for K >1 m/day (Barron et al.
2010) and the recharge values for selected soils represent the range of recharge estimates. A
set of analyses was undertaken to define the effect of historical climate characteristics
between 1930 and the present, and climate type on recharge, and to clarify:

what is the relative importance of annual rainfall, temperature, solar radiation and vapor
pressure deficit (VPD) in recharge estimation?

how rainfall intensity influences recharge?

what is the sensitivity of recharge to change in rainfall (recharge elasticity)?

where episodic recharge is most likely?
A summary of the analysis results are provided below and also given in Appendix 3.
In agreement with other published data (see Chapter 1), for all climate types total annual
rainfall and rainfall intensity were identified as the main factors influencing diffuse recharge.
However, a reduction in annual rainfall leads to a greater effect of other climate
characteristics on recharge, which in turn increases recharge sensitivity to changes in annual
rainfall. In addition, rainfall seasonality, which varies between climate types, was identified as
an important factor in annnual recharge estimation.
Relative importance of climate characteristics was defined using multiple regression models
between annual recharge (estimated using WAVES model) and climate variables
(Goderniaux 2006), which allowed assessment of the contribution of climate characteristics to
explaining variance in annual recharge
(Barron et al. 2010). For all analysed data, annual rainfall had higher relative importance than
other considered climate characteristics, including mean annual temperature, VPD and solar
radiation, cumulatively (Figure 18). However, the rainfall importance reduces under lower
annual rainfall (see Figure 68 in Appendix 3) to its minimum in the regions with annual rainfall
of 400–450 mm. These regions largely coincide with arid climate types with particularly low
recharge under climate type Bsk. When annual rainfall is lower than 400 mm, such as under
desert climate type Bwh, it appears that the relative rainfall importance tends to increases. It
is important to note that the relative importance of rainfall in recharge estimation reduces
under soils with lower permeability, particularly under trees and perennial vegetation, where
overall recharge is low and likely to be episodic in nature.
3
Weighted hydraulic conductivity (Kw) is estimated based on the hydraulic conductivity for two modelled soil layers
(k1 and k2) and the thickness of those layers (m1 and m2): K w  (k1m1  k2 m2 ) /( m1  m2 )
NATIONAL WATER COMMISSION — WATERLINES
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A reduction in annual rainfall also leads to an increase in relative importance of climate
characteristics other than rainfall in recharge estimation (Figure 20). Compared to VPD and
solar radiation, mean annual temperature has the lowest relative importance for all climate
types. This is likely to be due to a relative consistency of mean annual temperature within
individual climate type over the historical period (see Figure 2 in Chapter 2).
Overall, climate characteristics other than rainfall cumulatively explain on average 15 per cent
of the variability of recharge, with a maximum of 30 per cent. The higher effect of VPD, solar
radiation and mean annual temperature on recharge is related to the climate types with
summer-dominated rainfall (climate types Aw and Cfa), when the rainfall period coincides with
the period of a higher rate of potential evaporation and vegetation growth. In such conditions
VPD, solar radiation and temperature have a greater influence on evapotranspiration,
particularly evident for tree land cover, than under winter-dominated rainfall, leading to the
higher relative importance of these parameters on annual recharge estimation in Aw and Cfa
climate types (Figure 18 to Figure 20).
As opposed to regular recharge, which occurs every year, episodic recharge may take place
under the majority of investigated climatic conditions under a specific combination of soil and
vegetation (mainly under clay soil and trees). The exceptions are related to particularly highrainfall areas in the tropics (climate type Aw) and in the south-west under a temperate climate
with dry, warm summers (climate type Csb), and in the south-east in a temperate climate
without a dry season with a warm summer, where rainfall is greater than 700 mm.
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1.0
Aw
BWh
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.0
0.0
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.0
0.0
1.0
Csb
Csa
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.0
0.0
1.0
1.0
Cfa
Cfb
Ann
Per
Tree
Ann
Per
1.00
0.10
0.01
1.00
0.10
0.01
1.00
0.10
0.0
0.01
0.0
1.00
0.2
0.10
0.4
0.2
0.01
0.6
0.4
1.00
0.6
0.10
0.8
0.01
0.8
1.00
Relative importance
1.0
Relative importance
1.0
BSk
BSh
0.8
0.10
Relative importance
1.0
0.01
Relative importance
1.0
Tree
Soil hydraulic conductivity and vegetation type
mean annual rainfall
mean vapour pressure deficit
mean solar radiation
mean annual temperature
Figure 18: Relative importance of climate characteristics within considered climate types
under various soil and vegetation
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1.0
0.4
0.9
Aw
BSh
BSk
BWh
Cfa
Cfb
Csa
Csb
0.7
0.6
0.5
0.4
Aw
BSh
BSk
BWh
Cfa
Cfb
Csa
Csb
0.3
Ri (other)
Ri (rainfall)
0.8
0.2
0.1
0.3
0.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0.0
0.2
Mean annual rainfall (m)
0.4
0.6
0.8
1.0
Ri (rainfall)
Figure 19: Relationship between relative
importance of rainfall and mean annual rainfall
within considered climate types for perennial
vegetation and soil with K~1 m/day
Figure 20: Relationship between relative
importance of temperature, VPD and solar
radiation (cumulatively) and mean annual rainfall
within considered climate types for perennial
vegetation and soil with K~1 m/day
Relationship between modelled recharge and rainfall
As described earlier, sustainable groundwater yields in many regions are defined by a
percentage of rainfall that is expected to become groundwater recharge. Though it is
acknowledged that more sophisticated analyses are required for an accurate sustainableyield estimation, including groundwater modelling, the results reported in this section may
also support a better understanding of changes in the percentage of rainfall that becomes
recharge under various climate conditions.
A proportion of recharge in annual precipitation (rainfall) (R/P) varies between climate types
from less than 1 per cent under heavy soils, tree/perennial vegetation and arid climate (see
Figure 71 in Appendix 3) to nearly 70 per cent under annual vegeation and climate types with
high rainfall intensity (climate type Aw) and winter-dominated rainfall (climate types Csa and
Csb).
There is a non-linear relationship between recharge and rainfall, which is likely effect of
rainfall intensity or duration of consecutive days with rainfall. Increase in rainfall intensity, and
longer periods of rainfall, lead to an increase in annual recharge (as discussed in Barron et al.
2010), and both of these parameters are commonly greater under high annual rainfall (also
see Appendix 3). As a result, R/P is smaller under lower annual rainfall, which is true for both
individual modelling location or climate types and at the scale of the continent (Figure 21(a);
and Appendix 3). Therefore, the proportion of recharge in annual rainfall (R/P), even under
the same land cover and soil type, is not likely to be a constant; rather there is a functional
relationship between R/P = f(P) as shown in Figure 21(b). In the given examples this
relationship is shown to be linear.
This leads to another observation related to sensitivity of diffuse recharge to changes in
annual rainfall. Similar to the concept of the elasticity of streamflow (Chiew 2006), changes in
recharge are proportional to changes in rainfall but are not equal. It appears that changes in
annual rainfall lead to two- to four-fold greater change in recharge, meaning that under a 10
per cent reduction in rainfall recharge is likely to reduce by 20 per cent to 40 per cent (see
NATIONAL WATER COMMISSION — WATERLINES
46
Figure 72 in Appendix 3). The higher values in average recharge sensitivity to rainfall were
estimated for desert and arid climate types. Sensitivity of recharge to changes in annual
rainfall also increases when land cover includes perennial vegetation and trees. A summary
of recharge characteristics under considered climate types is given in Table 7.
1.0
(b)
Aw
Cs
Aw
0.6
Cs
0.4
0.2
Aw
Cs
Aw
0.8
R2 = 0.87
Recharge/Rainfall
0.8
Recharge (m)
1.0
R2 = 0.87
(a)
R/P = 0.52*P - 0.11
Cs
0.6
0.4
0.2
R/P = 0.29*P - 0.10
0.0
0.0
0.0
0.5
1.0
1.5
Annual rainfall (m)
2.0
2.5
0.0
0.5
1.0
1.5
2.0
2.5
Annual rainfall (m)
Figure 21: Relationship between a) modelled recharge and mean annual rainfall, and b)
between per cent recharge in rainfall and mean annual rainfall for perennial vegetation and
soil with K~1 m/day
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47
Table 7: Climate types and recharge
Climate types
savannah
Annual
rainfall
Aw
Recharge
Effect of climate types on recharge
8*
High-intensity rainfall under this climate type defines the strongest correlation between recharge and rainfall. The % rainfall which
becomes recharge is highest among all climate types for annuals, but under perennial and trees the % is similar or less than
those under the temperate climate (Csa, Csb and Cfb).
Tropical
This is likely to be due to the rainfall seasonality: under this climate type more than 70% of rainfall falls in summer. As this
coincides with the vegetation growth period and high rate of potential evaporation, water use by vegetation is greater and the
resulting recharge is lower under equal annual rainfall as in Csa, Csb or Cfb. This also leads to the high relative importance of
climate parameters other than rainfall in recharge estimations. After rainfall, solar radiation is the most important factor in
recharge estimation.
Sensitivity of recharge to change in annual rainfall is lowest among other climates under annuals (1.5), but it is similar to
recharge sensitivity to rainfall change under a temperate climate under other land cover types.
Cfb
without dry
season
with hot
summer
Cfa
7
Common patterns for temperate climate:
4
Total annual rainfall and rainfall intensity is
lower than for tropical climate type. The
importance of climate parameters other than
rainfall reduces for the climate types where
winter rainfall dominates (Csa and Csb). The
higher level of importance of climate
parameters other than rainfall is under a
climate with mainly summer rainfall (Cfa,
which is similar to Aw).
Temperate
without dry
season
with warm
summer
Reduction in rainfall
The possibility for episodic recharge is associated with inland regions under heavy soils and tree land cover.
Correlation between rainfall and recharge
reduces with reduction in rainfall, particularly
for rainfall less than 700 mm.
with dry
warm
summer
with dry
hot
Csb
Csa
6
5
Recharge sensitivity to change in rainfall is 2
to 4 for most combinations of soil and
vegetation. Generally, the sensitivity
increases for lower rainfall and under less
permeable soils and trees.
The possibility for episodic recharge is
associated with inland regions under a
combination of heavy soils and tree land
cover for Cfa and Cfb climate types.
The correlation between annual recharge and rainfall reduces significantly (R 2
<0.6) when annual rainfall is below 600 mm (inland areas).
The possibility for episodic recharge is associated with inland regions and for
the combination of heavy soils and tree land cover.
Among the temperate climate types, the rainfall intensity is higher in Cfa. The
rainfall intensity significantly reduces inland. The correlation between recharge
and rainfall reduces significantly (R2 <0.6) when annual rainfall falls below 800
mm (inland areas).
It is also characterised by the lowest relative importance of rainfall in recharge
estimations and the highest relative importance of other climate parameters
among the temperate climate types. After rainfall, VPD is the most important
factor in recharge estimation.
The possibility for episodic recharge is associated with inland regions and for
the combination of heavy soils and tree land cover.
The correlation between recharge and rainfall becomes weaker
(R2 <0.6) when annual rainfall is below 700 mm (inland areas).
After rainfall, VPD dominates in recharge estimation.
Because of higher permeability of soils, episodic recharge under this climate in
South-west Western Australia is not likely.
The correlation between recharge and rainfall becomes weaker
(R2 <0.6) when annual rainfall is below 500 mm (inland areas).
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48
summer
It is also characterised by the highest relative importance of rainfall in recharge
estimation and the lowest relative importance of other climate parameters
among the temperate climate types.
Because of higher permeability of soils, episodic recharge under this climate in
SWWA is not likely.
steppe hot
BSh
3
Common patterns for arid climate:
The recharge/climate parameters relationship
in arid climate types largely reflects those in
the neighbouring temperate (in the east) or
tropical (in the north) climate zone.
Arid
Recharge elasticity is on average higher than
in other climate types, but in contrast with
other climate types it is low under heavy soils
and perennial/trees vegetation, as recharge in
such conditions is extremely low.
steppe
cold
BSk
1
Relatively higher intensity of rainfall and high recharge rates are in the northern
regions (next to Aw climate type), where the correlation between recharge and
rainfall is the strongest. Lower rainfall intensity and much lower recharge are in
the eastern region (next to Cf climate type), where the correlation between
recharge and rainfall is much weaker than in the northern regions. Similarly, the
proportion of rainfall that becomes recharge is relatively lower in the eastern
regions compared to the northern regions.
The importance of temperature in recharge estimations is the highest among all
climate types, while rainfall remains the main factor influencing recharge.
The possibility for episodic recharge is associated with inland regions and for
the combination of heavy soils and perennials/tree land cover.
The lowest recharge/rainfall proportion out of all climate types. Overall the
lowest recharge rates in the country. This is mainly due to a particularly low
intensity of rainfall and the lowest rainfall importance. The correlation between
recharge and annual rainfall is weakest and recharge elasticity is among the
highest.
The possibility for episodic recharge is associated with inland regions and for
the combination of heavy soils and perennials/tree land cover.
desert hot
BW
h
2
The largest area of the country is under a desert climate type with the overall
lowest rainfall. However, recharge is on average greater than under the Bsk
climate type.
With particularly low rainfall, the importance of rainfall in recharge estimation is
greater than in some other arid climate types. Sensitivity to changes in rainfall is
not particularly different to that in other climate types. Episodic recharge is
possible under more permeable soils and all vegetation types.
* Recharge ranked from 1 (minimum) to 8 (maximum).
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49
Upscaling the point-scaling modelling to a national coverage
The point-scale modelling using WAVES provided an estimate of the long-term average
annual recharge across the country as a baseline to compare the recharge estimated under a
future climate. This was achieved by developing regression equations between the average
annual rainfall and the modelled average annual recharge for every combination of soil,
vegetation and climate type. These regression equations were then used along with rasters of
average annual rainfall and soil, vegetation and climate types to produce a raster of the
average annual recharge (Figure 22). Higher recharge is associated with tropical and
temperate climates (blue and green colour on the map). The lowest recharge (red colour) is
related to the areas of heavy clays.
Figure 22: Modelled historical annual average recharge across Australia for the period 1930–
2009 expressed in mm/yr (left) and as a percentage of rainfall (right)
The variability in the historical recharge was evaluated spatially on the basis of 15-year
periods within the 80-year baseline to compare the magnitude of the change in recharge due
to climate change to natural variability in the climate time series. The wet 15 years were
evaluated as the 10 per cent exceedence of 15-year periods within the 80-year baseline, the
median 15 years as the 50 per cent exceedence and the dry 15 years as the 90 per cent
exceedence. The results are presented as a recharge scaling factor (RSF). This is the
scenario recharge divided by the historical annual average recharge (Figure 23). In this way
an RSF of 0.5 indicates a 50 per cent reduction in recharge when compared to the baseline
scenario, and an RSF of 1.5 indicates a 50 per cent increase in recharge when compared to
the baseline scenario.
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50
Figure 23: Variability in recharge throughout the 80-year baseline scenario. The wet, median
and dry 15-year periods within the historical climate scenario compared to the 80-year annual
average recharge plotted as a recharge scaling factor (RSF).
Diffuse groundwater recharge under a future
climate
Projected changes in recharge under selected GCMs
The estimation of recharge under projections of future climate was modelled during this
project using three global warming scenarios for a 2050 climate, as described in Chapter 2.
The modelling was conducted using WAVES (Zhang and Dawes 1998) at a point scale for
100 points around the country and then upscaled on the basis of climate types, soil types,
vegetation cover and rainfall in the same way as done for the historical climate. The full
details of the modelling are described in an accompanying report (Crosbie et al. 2011a). The
results of this modelling are presented as an RSF. This is the scenario recharge divided by
the historical baseline recharge.
The RSF calculated for each GCM is quite different; in most regions around Australia there
are GCMs that project an increase in recharge, while others project a decrease (Figure 24).
The differences between the recharge projected by the 16 different GCMs are more variable
than the rainfall projected by them (Figure 5). This is discussed further below.
The number of GCMs that project either an increase or decrease in recharge is informative
(Figure 25). For the low global warming scenario, the majority of GCMs project a decrease in
recharge for the centre, west and most of the south of the continent. Across the north there
are large areas where the number of GCMs predicting a decrease in recharge is similar to the
number projecting an increase in recharge and other areas of the north where more than half
the GCMs project an increase in recharge. The trend with increasing global warming is for
more GCMs projecting an increase in recharge. This is most evident in the east of the country
where, for the high global warming scenario, there are few areas where most GCMs project a
reduction in recharge. A notable exception to this trend is in the south-west of Western
Australia (SWWA) where all GCMs for all scenarios project a decreaseIn contrast to the
rainfall analysis (Chapter 2), the projections for the southern MDB are not all for a decrease
for all scenarios for all GCMs.
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Figure 24: RSF rasters for the medium global warming scenario using an 80-yr baseline
NATIONAL WATER COMMISSION — WATERLINES
52
Figure 25: Number of RSF rasters that project a decrease in recharge from the 16 GCMs for
each global warming scenario
For each global warming scenario the 16 rasters of RSF were fitted to a weighted Pearson
Type III probability distribution to simplify the results down to three cases: a wet future, a
median future and a dry future. The weights are used to bias the results in favour of the
GCMs that better reproduce the historical climate, assuming that they are more likely to
project a future climate adequately. The weights were as determined by Smith and Chiew
(2009) and the full details of the method is documented in Crosbie et al. (2011a). In general,
the results of fitting the RSF rasters to a probability distribution show that the 10 per cent
exceedence is an increase in recharge, the 90 per cent exceedence is a decrease, and the 50
per cent exceedence is somewhere in between (Figure 26). For the 10 per cent exceedence
case there is a trend for increasing recharge with increasing global warming. This can be
seen as the blue colour is getting more intense and the area that is statistically significant is
increasing. A notable exception is in SWWA where, even at the wet end of the probability
distribution, a reduction in recharge is projected. This is expected because all GCMs project a
decrease in recharge in this region.
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53
Figure 26: The 10%, 50% and 90% exceedences from fitting the RSF rasters to a weighted
Pearson Type III distribution for each global warming scenario. The blacked-out areas are
where the change in recharge is not statistically significant.
For the 90 per cent exceedence case, the entire country shows a reduction in recharge. With
increasing global warming there is a trend for more areas across northern Australia to not
show a statistically significant change. This is again indicative of increasing recharge with
increasing global warming.
The simplified result from the Pearson Type III distribution has been calculated, as the wet
future scenario is the maximum of the 10 per cent exceedence from the three global warming
scenarios. Similarly, the dry future scenario has been calculated as the minimum of the 90 per
cent exceedence of the three global warming scenarios and the median future scenario has
been calculated as the median of the three
50 per cent exceedence rasters.
A comparison between the projected future recharge under a 2030 and 2050 climate can only
be attempted in areas where the previous sustainable yields projects used a similar
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54
methodology to that used here; these areas are the MDB (Crosbie et al. 2008), northern
Australia (Crosbie et al. 2009a) and Tasmania (Crosbie et al. 2009b) (Figure 27). The RSF
rasters are not directly comparable because of different assumptions made during these two
projects. For example, the wet, median and dry GCMs were selected based on reporting
regions for the sustainable yields projects. This can be seen as edge effects along reporting
region boundaries (particularly the MDB). As a gross generality, the trends between 2030 and
2050 are similar.
Figure 27: A comparison of the RSF for a 2030 climate from the sustainable yields projects
and the RSF for a 2050 climate from the current project
Relationship between change in rainfall and change in
recharge
If there is a relationship between the projected change in rainfall and the projected change in
recharge then the modelling results presented here can be substantially simplified. This is
similar to the concept of the elasticity of streamflow (Chiew 2006), whereby the change in
streamflow can be predicted from the change in rainfall. This is illustrated in Figure 28 for two
contrasting cases: Tomago (New South Wales) and Gnangara (WA). At Tomago, it can be
seen that the slope of the change in rainfall and change in recharge relationship for each
global warming scenario is almost the same. However, the intercept widens with the
increasing global warming scenario. This suggests that the sensitivity of the change in mean
annual recharge to the total change in mean annual rainfall is constant for the different global
warming scenarios. but the sensitivity of the change in recharge to climate parameters. other
than total annual rainfall, rises with increasing global warming. The intercept term in this
relationship is likely to incorporate changes in rainfall intensity, rainfall seasonality,
NATIONAL WATER COMMISSION — WATERLINES
55
temperature and CO2 concentration. The slope of the relationship is 2.7 for all three global
warming scenarios, with the intercept increasing from –2 for the low global warming scenario
2
to +20 for the high global warming scenario. The r for all three scenarios is 0.81. At
2
Gnangara, the relationship is not as consistent as Tomago. The r decreases with increasing
global warming from 0.84 for the low scenario down to 0.45 for the high scenario. The
relationship for the high global warming scenario is not statistically significant (p <0.05).
This relationship between the change in rainfall and the change in recharge can be calculated
for each pixel in the national scale rasters (Figure 29). Nationally, the results are similar to
those at Tomago; the slope is very consistent at a point between global warming scenarios,
but the intercept increases with increasing global warming. This represents an increase in
recharge with increasing global warming, independent of changes in the total rainfall.
80
80
Tomago
60
40
Gnangara
High global warming
Medium global warming
Low global warming
60
40
20
R (%)
20
R (%)
High global warming
Medium global warming
Low global warming
0
0
-20
-20
-40
-40
-60
-60
-80
-80
-40
-20
P (%)
0
20
-40
-20
0
20
P (%)
Figure 28: Examples of the relationship between the change in rainfall and the change in
recharge at Tomago (NSW) and Gnangara (WA) for each global warming scenario using all
16 GCMs (point-scale modelling). No line is plotted at Gnangara for the high global warming
scenario as the relationship is not statistically significant.
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56
Figure 29: Change in rainfall–change in recharge relationships under a 2050 climate. The
areas shaded black are where the relationship is not statistically significant.
Effect of climate change and climate variability on recharge
It was found that the historical variability in recharge (Figure 23) is greater than the difference
in recharge under the wet and dry future climate scenarios (Figure 27). To investigate the
combined effects of climate change and climate variability on recharge, we have evaluated
RSFs for the combinations of four different climates (historical, wet future, median future and
dry future) and three different variabilities (wet 15 years, median 15 years and dry 15 years)
(Figure 30). The RSFs for each of these 12 scenarios for every GMU is tablulated in Crosbie
et al. (2011a).
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57
Figure 30: A matrix of 12 RSF rasters comprised of four different climates (dry, median and
wet future climate and historical climate) and 15-year variabilities (dry, median and wet) for
the 80-year baseline
Effect of climate change on localised recharge
Localised recharge from river systems can be a major source of renewable groundwater
resources, particularly in alluvial aquifers. Recharge associated with the losing streams and
overbank flooding is the dominant recharge mechanism for many priority aquifers identified in
this report (Chapters 3 and 6). The changes in localised recharge under a future climate are
likely to be linked to changes in river flow, including frequency and duration of floods.
A recent study of climate change has indicated projected changes in the runoff across
Australia (Chiew et al. 2009). Figure 31 shows the effect of rainfall change on mean annual
runoff for future dry, median and wet scenarios. In many areas the larger projected changes
in annual runoff may result in small changes in runoff due to overall small absolute runoff
values. The changes in runoff are expected to have corresponding impacts on stream
discharge and a follow-up effect on surface water and groundwater interaction.
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58
Figure 31: Wet, median and dry (from left to right) estimates of change in future mean annual
o
runoff for a 1 C global warming (~2030 relative to 1990) (Chiew 2010)
The effect of climate change on localised recharge is largely attributed to changes in riverflow duration, river stages and the extent of inundated areas, which are particularly significant
during flooding. Depending on river-channel morphology, changes in river flow lead to an
increase or a decrease in the river stage and/or the river’s effective width. During most
frequent-flow events, river flow is contained within a river channel, but under extreme flow
conditions (floods) the increase in river flow leads to greater changes in width of the
inundated area compared to the associated changes in a river stage. The duration of no-flow
periods in intermittent rivers is another important characteristic that may significantly influence
both recharge rates and their changes under future climate scenarios.
Though there have been a few local investigations related to groundwater recharge from
rivers and floods (e.g. Middlemis 2010), at a national scale such studies are limited. There is
also limited data related to projection of climate change impacts on river flooding and the
extent of associated inundation areas. One study is reported for the MDB, where the extent of
historical floods was mapped together with projected changes in flood areas under future
climate scenarios (Figure 32) (Overton et al. 2010). The effects of different climate scenarios
of the flooding extent, as studied in the MBDSY project, were analysed by Doody et al. (2009)
and Overton et al. (2010) and found to differ from location to location. At the same time, the
floods of given return periods have also changed over the past few decades and are
projected to change in the future. This has led to changes in inundation areas, thus affecting
the flood-recharge volume. For example, in Chowilla floodplain, areas that were indundated
by a one-in-10 year return-period flood no longer get inundated under a flood of same return
period. These inundated areas are projected to contract futher under future climate change;
the innundation area under median future climate scenario is projected to decrease by 31 per
cent compared with historical area (Doody et al. 2009).
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59
Figure 32: Flood change map for the Murray-Darling Basin under historical, current (Scenario
A) and future (median future climate scenario) MDBSY modelled scenarios (adopted from
Overton et al. 2010); note that current scenario (Scenario A) is not used in this project
Because of the specifics of localised recharge (discussed in Chapter 1 and Appendix 4) and
difficulties in its estimation or measurement, the assessment of changes in localised recharge
under changing climate conditions at a national scale within the current project has been
attempted on a conceptual basis. There are other NWC projects designed to improve current
knowledge of the surface and groundwater interaction. On the completion of those projects,
the assessment of changes in localised recharge under changing climate conditions could be
further advanced. In this project the main goal was to define how changes in river flow under
future climate scenarios may influence changes in localised recharge, but recharge estimation
was not included in the scope of analysis.
As shown in Appendix 4, losing streams may be either hydraulically connected to
groundwater systems or disconnected. The fluxes between connected river and groundwater
can be described by Darcy’s Law: QR
 kb( H riv  H gw ) / L , here given for recharge (QR)
estimation from a unit length of the river. The fluxes from the disconnected rivers to
groundwater are defined by the unsaturated flow conditions. For these two types of losing
streams, the effect of river flow on localised recharge may vary:

For connected rivers, the changes in localised recharge as a result of the variations in river
flow and within an individual river reach are given by the changes in both river stage (Hriv)
and the effective river width (b). The former influences the hydraulic gradient and therefore
fluxes between a river and groundwater, while the latter defines the area from which
localised recharge occurs. The sensitivity to changes in localised recharge to the river-flow
variation is also influenced by changes in the depth to groundwater (Hgw), which, along with
river stage, influences the hydraulic gradient and therefore fluxes between a river and
groundwater.
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
For disconnected rivers, changes in localised recharge are largely defined by changes in
the effective river width, which defines the area where localised recharge occurs. In such
streams the recharge rates are largely controlled by the hydraulic properties of streambed
materials defining the suction potential and unsaturated hydraulic conductivity, and it was
shown (Osman and Bruen 2002) that river stage has negligible effect on recharge rates.
In both cases hydraulic properties of riverbeds and their distribution along or across the
channel are the key factors defining a localised recharge rate. However, when the changes in
recharge are considered within an individual river reach but under various flow conditions, the
effect of hydraulic properties of a riverbed is likely to be less important. The exceptions may
be related to circumstances when there is a significant variation in hydraulic properties of
riverbed materials, and under changing flow conditions there may be a variation in recharge
rates within various extents of inundated areas within a river channel or on floodplains.
It is likely that the changes in river flow may have different levels of impact on localised
recharge. In wide and flat river channels, the changes in the river flow are predominantly
associated with changes in the effective width of the river. For narrow river channels with
steep banks the changes in the river flow are predominantly associated with changes in river
stage but have a limited effect on the effective river’s width.
Approach to the evaluation of localised recharge change
under changing climate
The adopted methodology was based on simultaneous calculation of Manning’s and Darcy’s
equations (Appendix 4). The former links river flow with river stage (Hriv) and river width (b) for
a specified river channel morphology. Darcy’s equation was used to define the rate of water
losses from a unit length of a river (1 m) under steady-state conditions for the identified river
stage (Hriv) and river width (b). The thickness of riverbed deposits and their hydraulic
properties, though important for recharge estimation, were neglected when the relative
differences in recharge were considered.
Both historical and projected future river-flow data is required for analysis as well as
knowledge of where rivers are ‘losing’, which leads to limitations of the data sources. As a
result, the river-flow data modelled within the MDBSY area at a series of river reaches, which
are also underlain by high-priority aquifers (Chapter 3), were analysed. The selected reaches
of losing streams and gauging stations along those reaches are shown in Figure 33. The flow
data from four climate scenarios (historical, future dry, medium and wet climate) were
analysed to investigate the effects of changes in river flow under a future climate with possible
implications for in-stream recharge.
For all identified locations, the data on river-channel morphology and/or the flow rates
associated with flooding was not available. Hence the analysis was undertaken to identify the
relative changes in recharge under conditions where changes in river flow result in changes in
river stage under a range of selected river effective widths, with the assumption that the
riverbed is characterised by trapezoidal cross-sectional shape with steep banks (10-to-1). In
this analysis the effect of changes in river flow under future climate scenarios was estimated
for connected rivers and some outcomes of this analysis were further inferred to disconnected
rivers.
This approach was used to evaluate relative changes in recharge dR = 100(Rf-Rh)/Rh caused
by changes in river flow under future climate scenrios dQ = 100(Qf-Qh)/Qh, where Rh and Rf
are estimated recharge under historical and future climate conditions, while Qh and Qf are
modelled river flow under historical and future climate conditions. The modelled river-flow
data for historical and futute wet, medium and dry climate scenarios sourced from the MDBSY
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database is presented as flow-duration curves (Figure 34). These were further used for dR
calculation. The results of the analysis are reported as the ratio of change in relative change
in recharge and changes in river flow under future climate scenarios (e = dR/dQ), describing a
sensitivity of localised recharge to changes in river-flow conditions.
Assumptions and limitations of this approach are discussed in Appendix 4. Though
conceptually simplified, the described approach allowed for examining and illustrating the
general relationships between changing localised recharge and river flow and the effects of
various parameters that influence this relationship.
Figure 33: Location of stations along the losing streams analysed for effects of climate
change on river discharge
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1000000
40
(a)
(b)
Historical
30
Dry
Change in river flow (%)
Daily river flow (ML)
Median
Wet
100000
10000
20
10
0
-10
-20
-30
1000
-40
0
20
40
60
80
100
Percent time daily river flow is exceeded
0
20
40
60
80
100
Percent time daily river flow is exceeded (historical)
Figure 34: Presentation of the modelled flow data for a) historical and future climate scenarios
and b) flow changes under future climate scenarios relative to historical river flow
Projected changes in the river flow
Though surface water availability across the MDB is projected to decline overall because of
climate change (CSIRO 2008d), there are some ranges in this projection. For example, under
the dry future climate scenario surface water availability could reduce by as much as 34 per
cent by 2030 or increase by up to 11 per cent under the wet future climate scenario. The
decline is expected to be greatest in the south-east where most of the runoff is generated and
where the impacts of climate change are projected to be greatest.
For the selected rivers, the average change in streamflow across all flow frequencies ranges
from minus 38 percent (dry future) to plus 44.3 per cent (wet future), relative to the streamflow
under the historical climate (Figure 35). The reduction in river flow is projected for both future
median and dry climate scenarios. These reductions in river flow follow a pattern of relative
change in rainfall in the region (Figure 36). The larger differences are projected for extreme
streamflow events with low frequencies. As the flow rate associated with flooding was not
known, a flow of 10 per cent exceedence probability was used as its substitute from 15
stations (Figure 37). For all stations, flow volume for this probability was projected to increase
under the wet-future climate scenario and to reduce under dry future and median future
climate scenarios, relative to historical. There are also projected changes in the duration of
flows in the streams. Figure 38 shows the probability of no-flow periods at 15 stations for the
historical, future dry, median and wet climate scenarios. The duration of streamflow changes
under the future climate scenarios at only five rivers. For these streams, probability of zero
flows under a future wet climate is lower than that under the historical climate, implying a
decrease in the duration of a period with no flow.
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100
410001
416026
418032
419012
419027
419039
419049
420004
420005
421023
421039
422015
422025
422358
422394
Mean change in river flow (%)
75
50
25
0
-25
-50
-75
-100
Dry
Median
Wet
Figure 35: Average change in streamflow across all flow frequencies relative to streamflow
under the historical climate for the selected rivers
15
410001
416026
418032
419012
419027
419039
419049
420004
420005
421023
421039
422015
422025
422358
422394
Mean change in rainfall (%)
10
5
0
-5
-10
-15
-20
Dry
Median
Wet
Figure 36: Average change in rainfall for all future climate change scenarios from the
historical climate at regions representing the 15 chosen stations
100
410001
416026
418032
419012
419027
419039
419049
420004
420005
421023
421039
422015
422025
422358
422394
Mean change in river flow (%)
75
50
25
0
-25
-50
-75
-100
Dry
Median
Wet
Figure 37: Changes in streamflow with 10 per cent exceedence probability for three future
climate scenarios (future dry, median and wet climate) relative to historical climate
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Duration of no-flow period (%)
100
Historic
80
Dry
Median
Wet
60
40
20
94
23
58
42
23
25
42
20
15
42
20
39
42
10
23
42
10
05
42
00
04
42
00
49
42
90
39
41
90
27
41
90
12
41
90
32
41
80
26
41
60
41
41
00
01
0
Figure 38: Per cent of time with no flow at the station; streams with zero values are the
perennial stream
Projected changes in localised recharge
Localised recharge from the river channels
An example of the results for the Murrumbidgee River (Node 410001) is given in Figure 39,
while the results for other locations are given in Appendix 4. The range of dR shown (by
green band) in Figure 39 is due to a range in the assumed river width. The greater changes
(dRmax) are likely to occur if the changes in the river flow are predominantly associated with
changes in the effective width of the river (wide and flat river channels). The lower changes
(dRmin) are related to the river reaches where the changes in the river flow are predominantly
associated with changes in the river stage (narrow river channels with steep banks).
Overall, the increase in river flow under a future wet climate scenario leads to an increase in
localised recharge from losing connected streams, while the projected reduction in river flow
under future median and dry climate scenarios causes a reduction in localised recharge. The
results indicate that changes in localised recharge are lower than those in river flow when the
depth to groundwater remains constant, as shown in Figure 40 when compared to Figure 36.
For a flat river reach, recharge sensitivity to changes in river flow (e = dR/dQ) is, overall, high
(Figure 41). When changes in river flow mainly result in changes in the river stage, the
sensitivity of localised recharge is much lower. In both cases sensitivity increases under
higher river-flow rates.
The sensitivity of localised recharge to changes in river flow reduces when the depth to
groundwater is increased (but remains constant between historical and future climate
scenarios). Figure 42 shows that for rivers where changes in flow resulted mainly in changes
in the effective width: dR/dQ = 0.40 for Hgw = 1 m, but reduces to 0.15 for Hgw = 6 m. An even
a greater reduction in sensitivity of localised recharge to changes in flow is likely to occur in
the rivers where flow changes mainly lead to changes in the river stage: dR/dQ = 0.08 for Hgw
= 1 m, but reduces to 0.015 for Hgw = 6 m. Such reduction in localised recharge sensitivity is
due to a smaller effect of the river stage on the hydraulic gradient between river and
groundwater table, and hence greater recharge rates with a greater depth to groundwater .
However, there is an opposite result when the depth to groundwater changes under the future
climate scenarios. If groundwater depth increases under the future climate scenarios, there is
a projected increase in localised recharge (Figure 43) and vice versa: if groundwater depth
rises under the future climate scenarios, there is a projected reduction in localised recharge.
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The effect of changes in river flow on localised recharge may also vary depending on the river
slope, which largely controls river-flow velocity: the higher the slope, the higher the velocity.
Accordingly, under an equal-flow and riverbed morphology, the river stage is less for steeper
slopes. This is expected to have a follow-up effect on localised recharge, as illustrated in
Figure 44. It shows that the sensitivity of localised recharge to changes in river flow increases
for the rivers flowing within flat terrains (S = 0.0001–0.0005) such as the lower Murray–
Darling regions.
When disconnected rivers are considered, the changes in localised recharge under future
climates will be defined by the effect of the river-flow alteration on the effective river width. As
a result, it is expected that the relative changes in localised recharge are likely to be
proportional to changes in river flow in wide and flat river channels, where the flow changes
are predominantly associated with those in the effective width of the river. For narrow river
channels with steep banks, changes in the river flow are predominantly associated with
changes in the river stage. As such, they may have limited effect on the river’s effective width.
For such conditions the relative changes in localised recharge from disconnected streams are
likely to be minimal or none.
(a)
0
-10
-20
-30
dQ_Dry
dR_Range
Changes relative to historical climate (%)
-40
(b)
0
-5
-10
-15
dQ_Median
dR_Range
-20
(c)
40
dQ_Wet
dR_Range
30
20
10
0
0
10
20
30
40
50
60
70
80
90
100
Percent time daily river flow is exceeded (historical)
Figure 39: Changes in the Murrumbidgee River flow and the range of changes in localised
recharge for dry, median and wet future climate scenarios
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Maximum dR (%)
20
(a)
10
410001
416026
418032
419012
419027
419039
419049
420004
420005
421023
421039
422015
422025
422358
422394
0
-10
-20
Minimum dR (%)
20
(b)
10
0
-10
-20
Median
Dry
Wet
Figure 40: Average changes in the localised recharge across all flow frequencies relative to
localised recharge under the historical climate for the selected rivers (for Hgw = 1 m)
0.6
0.5
0.5
0.4
Maximum
dR/dQ
dR/dQ
Minimum
Maximum
0.4
Minimum
0.3
0.3
0.2
0.2
0.1
0.1
0.0
0.0
0
30000
60000
90000
120000
150000
0
Daily river flow (ML)
1
2
3
4
5
6
Depth to watertable (m)
Figure 41: Relationship between sensitivity of
localised recharge, e, to changes in river
flow, and daily river discharge under
historical climate conditions (for
Murrumbidgee River)
Figure 42: Sensitivity of localised recharge to
changes in river flow for various initial depths
to groundwater, which remain unchanged
under the future scenarios (for Murrumbidgee
River)
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7
0.5
6
Minimum
Maximum
5
dR/dQ
4
dR/dQ
Minimum
Maximum
0.4
3
2
0.3
0.2
1
0.1
0
-1
0.0
0
1
2
3
4
5
6
0.000
Depth to watertable (m)
0.002
0.004
0.006
0.008
0.010
0.012
River slope
Figure 43: Sensitivity of localised recharge
to changes in river flow for various changes
in depth to groundwater (for Murrumbidgee
River): 1m watertable depth was assumed
for the historical scenario
Figure 44: Sensitivity of localised recharge to
changes in river flow for various river slopes
(for Murrumbidgee River)
Localised recharge associated with floods
There are large differences in localised recharge sensitivity to changes in river flow depending
on river morphology, suggesting that substantial changes in localised recharge rates are likely
during overbank flow. Overbank flow leads to a relatively large increase in the effective river
width for a lesser change in the river stage. To examine some aspects of the effects of river
morphology on dR, a composite trapezoidal river section was used for analysis. In this case
the river channel remained unchanged and only changes in a floodplain width were
anticipated.
For the conditions when overbank flooding occurs, the relationship between dR and dQ is
shown to be different (Figure 45). dR may become much greater than dQ, when the floods
are likely to be more frequent under the future climate scenarios (wet) and much lower than
for dQ, when the floods are likely to be less frequent under the future climate scenarios
(median and dry). However, the relevant contribution of localised recharge from losing
streams compared to the contribution associated with floods may require further analysis.
Such analysis, even on a conceptual level, requires a prior knowledge of river morphology.
Unfortunately, information on river morphology and flow rates associated with flooding was
not available for modelled river stations. Some anlaysis was further undertaken for Chowilla
floodplain to confirm this observation.
Though groundwater use is limited because of high salinity, the Chowilla floodplain was
considered because a sufficient set of data existed at this location to allow for the estimation
of potential localised recharge under various flooding events. Data relating to the changes in
frequencies of those events under the future climate scenarios was also available.
The extent of the Chowilla floodplain inundation was estimated using the River Murray
Floodplain Inundation Model (RiM-FIM), which links recorded river flows at regulation points
(locks) to the spatial extent of flooding derived from satellite imagery (Figure 46; Overton et al.
2010). This allowed an examination of the extent of inundation under given flow rates and an
estimation of the volume of recharge that would occur under historical and future climate
2
scenarios. The extent of the area considered for this analysis was approximately 200 km .
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150
(a)
dQ_Dry
dR_Min
100
dR_Max
50
0
Changes relative to historical climate (%)
-50
150
(b)
dQ_Median
dR_Min
100
dR_Max
50
0
-50
150
(c)
dQ_Wet
dR_Min
100
dR_Max
50
0
-50
0
10
20
30
40
50
60
70
80
90
100
Percent time daily river flow is exceeded (historical)
Figure 45: Changes in localised recharge under future climate scenarios defined for a
composite trapezoidal channel (the river channel remains unchanged and hence a single line
is associated with the period of river flow contained within the channel; the only changes are
associated with floodplain width, and changes in recharge during flooding are shown in green
and pink colour for narrow and wide floodplains): a) for dry future climate; b) for medium
future climate; and c) for wet future climate
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Figure 46: The location of the Chowilla floodplain, a) the recharge estimates used to
determine climate change impacts on localised recharge derived from flood inundation events
and b) the extent of inundation for given flow rates (Overton et al. 2006)
Combined consideration of the extent of the floodplain inundation for various daily flow rates
(from 30 000 ML/day to a maximum of >190 000 ML/day, with 10 000 ML/day increments)
and the range of daily recharge rates within the inundated area allowed the estimation of daily
recharge volumes under various flow conditions. Based on the inundation duration, the total
recharge volumes were further calculated for the range of flow rates.
Based on river-flow duration curves (FDCs) for historical data and future median and dryclimate scenarios, the frequencies of flow rates used in the recharge anlaysis were estimated.
Using the projected frequencies of flow events, the associated recharge volumes were plotted
similarly to FDCs, but showing ‘recharge’ duration for future median and dry climate scenarios
(Figure 47). Finally, the changes in recharge volumes under the future climate were estimated
(Figure 48). It appears that changes in localised recharge associated with flooding are much
greater than projected changes in river flow. As discussed earlier, this is likely to be
associated with a significant increase in river width during flood events. There is also an
additional effect of variation in land cover and soil type within the innundated areas under
various flood extents.
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1000000
100000
(a)
(b)
Historical
Dry
Recharge volume (ML)
Daily river flow (ML)
Median
100000
10000
1000
100
10000
10
0
5
10
15
20
25
0
Percent time daily river flow is exceeded (historical)
5
10
15
20
25
Percent time daily river flow is exceeded (historical)
Figure 47: Duration curves for a) Chowilla daily river flow (426510) for historical, future dry
and future medianclimate scenarios and b) estimated recharge volumes from floodplain
inundation under those climate scenarios
Changes relative to historical climate (%)
150
dR_Dry
100
dR_Median
dQ_Dry
dQ_Median
50
0
-50
-100
-150
0
5
10
15
20
25
Percent time daily river flow is exceeded
Figure 48: Projected changes in recharge volumes (dR) and river flow (dQ) from floodplain
inundation for future median and future dry climate scenarios relative to historical climate
Conclusions
The analysis of climate and its change on renewable groundwater resources allowed drawing
the following conclusions related to recharge estimation under historical and future climate
conditions.
Historical climate and groundwater recharge
Consistent with previous work, the magnitude of recharge is greater under high rainfall
compared to low rainfall, annual vegetation compared to native vegetation and lighter textured
soils compared to finer textured soils.
Annual rainfall is, overall, the most important parameter in recharge estimation. However, its
relative importance reduces under lower rainfall conditions, and along with that there is an
increase in the relative importance of other climate parameters in recharge estimation
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(temperature, solar radiation and vapour pressure deficit). The effect of climate parameters
other than rainfall on recharge is greater under climate types with summer-dominated rainfall.
An increase in rainfall intensity leads to an increase in recharge, a higher proportion of rainfall
that becomes recharge, an increase in the relevant importance of rainfall, and a reduction in
the relevant importance of other climate parameters in recharge estimation.
There is a non-linear relationship between recharge and rainfall, which is likely due to the
effect of rainfall intensity or duration of consecutive days with rainfall. Therefore, a proportion
of recharge in annual rainfall (R/P) is not likely to be a constant—even under the same land
cover and soil type.
Changes in recharge are largely proportional to changes in rainfall but not equal. It appears
that changes in annual rainfall lead to two to four-fold greater changes in recharge.
Episodic recharge may take place under the majority of investigated climatic conditions under
specific combinations of soil and vegetation (mainly under clay soil and trees).
The variability of recharge in 15-year periods compared to the long-term average is greater in
areas of low recharge, whereas the range between wet and dry 15-year periods is
comparatively smaller in high-recharge areas.
Projected changes in diffuse groundwater recharge
The 16 GCMs used in the analysis are not consistent in their projections of recharge, except
in south-west Western Australia where all GCMs project a decrease in rainfall and the
recharge derived from it. The number of GCMs that predict a decrease in recharge decreases
with increased global warming for most of the country. An exception to this is for parts of the
south of the country, where all GCMs project a decrease in recharge.
The median future climate projects a decrease in recharge across most of the west, centre
and south-east of Australia; however, increases in recharge are projected across northern
Australia and a small area of eastern Australia. The dry future climate projects a decrease in
recharge everywhere in Australia. The wet future climate projects an increase in recharge
everywhere except for south-west Western Australia and a few other localised areas of
southern Australia.
The projections made for 2030 during the sustainable yields projects are generally consistent
with those made for 2050 in the current project.
The relationship between change in rainfall and change in recharge has a consistent slope
between global warming scenarios but a different intercept. This indicates that the sensitivity
of the change in recharge to the change is rainfall is relatively constant, but changes in factors
other than total rainfall result in an increase in recharge (e.g. CO 2 concentration, temperature
and/or rainfall intensity).
The most extreme scenarios considered here are a wet 15-year period within a wet future
climate and a dry 15-year period within a dry future climate. At a GMU scale, the wet extreme
can project increases in recharge of more than 300 per cent of the historical average and the
dry extreme less than 10 per cent of the historical average.
Projected changes in localised groundwater recharge
Changes in localised recharge due to climate change are likely to be similar to projected
changes in river flow from disconnected losing streams, but lower than projected changes in
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72
river flow from connected losing streams. For connected rivers the changes in localised
recharge under future climate scenarios are likely to be similar or less than the changes in
rainfall. For both cases the impact on localised recharge is likely to be more significant in the
rivers with wide, flat channels and in the lower valleys, where the river slopes are small.
Localised recharge sensitivity to changes in river flow reduces in areas with deeper
groundwater. An increase in groundwater depth under future climate scenarios is likely to
cause an increase in localised recharge from connected losing streams even under conditions
when river-flow reduction is projected.
For the conditions when overbank flood occurs, changes in localised recharge may become
much greater than projected variation in river flow. For example, in the Chowilla floodplain the
change in recharge volumes may reach up to 100 per cent, while the change in river flow is
projected to be about 20 per cent.
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4. Climate change impacts on
groundwater resources in different
aquifer types
Groundwater systems are dynamic in nature, with spatial and temporal variations in their
inputs and outputs. Climate change can affect both the condition (such as water quality) and
amount of resource in a groundwater system. The impacts of climate change on groundwater
resources are influenced by changes in diffuse and localised recharge, and diffuse and
localised discharge, as well as changes in water demand, and therefore groundwater
abstractions rates. Some of these factors have been discussed in previous chapters, but it is
the analysis of the combination of all the factors in a groundwater model that provides an
assessment of the impact on the resource.
This chapter provides a brief review of the groundwater modelling done as part of the
sustainable yields projects in the MDB, northern Australia, south-west Western Australia and
Tasmania, and subsequent work done through the MDBA for subcatchments of the MDB
(Figure 49). This modelling examined the impact of future climate projections and expansion
of human activities in terms of changes to water balance fluxes and water levels.
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Figure 49: Location of the reviewed groundwater models
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Hydrogeological setting of modelled aquifers
Aquifers with detailed numerical models can be grouped into two broad categories: alluvial
and sedimentary. This does not mean that the entire groundwater system is alluvial or
sedimentary but that the most exploited parts of it are. As a result, groundwater models were
developed for those areas only. This general partitioning impacts on the processes that are
modelled in each aquifer type, the scale of flux to and from aquifers, and therefore the
sensitivity of water resources to changes in water balance caused by climate change. In
addition some aquifers hosted by limestones are karstic (e.g. some parts of the Daly Basin in
northern Australia), and it is difficult to parameterise and model large voids as flow in these
conditions may not comply with the Darcy’s flow conditions. This has implications for recharge
and discharge estimation as a result of the assumption that large voids are treated as an
equivalent porous medium. In reality though, both recharge and discharge processes could
happen through preferential flow paths.
The alluvial systems discussed here are within the inland subcatchments of the MDB. They
are typically described as systems with a relatively low hydraulic conductivity upper layer
composed of sand, silt and clay. In the models this upper layer also contains a river. This
layer also confines a lower layer that is composed of sand and gravel, has relatively higher
conductivity and is therefore the source of most of the extracted water. In the northern parts of
New South Wales, the formations are named Narrabri over Gunnedah, in central New South
Wales they are Cowra over Lachlan, and in southern New South Wales and northern Victoria
they are Shepparton over Calivil. Most of the models do not include the surrounding
geological material, and therefore the type of the bedrock is often not recorded in the
modelling summaries.
The representation of these layers in the models is generally very simple; each of them is
usually modelled as a single computational layer. There are some exceptions where the
upper layer is particularly thick. For example, the confining layer may have downward grading
of material leading to sublayers of higher and lower productivity, such as in the Southern
Riverine Plains (SRP) and Upper Lachlan models, so separating this sequence in an
individual layer is reasonable. A third deeper layer, also highly productive, is present in some
catchments, i.e. Cubbaroo in Lower Namoi, and Renmark in Lower Lachlan, Lower
Murrumbidgee and SRP. Connection to the GAB, either as an input or output, is included in
the models for Lower Namoi and Lower Macquarie.
The Upper Condamine and Lower Macquarie do not follow this general pattern. In these two
areas the aquifer is a series of well-connected layers that form, conceptually, a single unit.
Here there is no distinct overlying lower hydraulic conductivity layer. However, conditions
locally may be unconfined to semiconfined depending on differences in vertical hydraulic
conductivity and whether a groundwater head is above or below the base of the confining
layer.
The sedimentary systems are coastal catchments in Western Australia, the Northern Territory
and Tasmania. They typically have a vertical sequence of distinct layers, sometimes
alternating aquifers and aquitards, with a trend of decreasing hydraulic conductivity of
productive aquifer with increasing depth. They are commonly modelled as a series of
horizontal layers with hydraulic conductivity that may or may not be related to an individual
stratigraphic unit.
In coastal Western Australia there are three major aquifers: sandy, unconfined, superficial;
sandstone and siltstone; and Leederville and Yarragadee. In the Perth region they are
essentially layered horizontally and the complexity of layering and the thickness of layers are
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represented in 13 model layers (in the Perth Regional Aquifer Modelling System or PRAMS
model). In the south-west these formations form the upper wing of a syncline and, as such,
the layers are not horizontal. As a result, part of the formations are weathered with
extensive outcropping of a clay-rich aquitard commonly found between the Leederville
and Yarragadee Formations, and local outcropping of the deep Yarragadee Formation. The
groundwater model here contains eight model layers (the South-West Aquifer Modelling
System or SWAMS). The area between the extent of PRAMS and SWAMS domains was
covered by a simpler model of the Peel-Harvey region (the Peel–Harvey Regional Aquifer
Modelling System or PHRAMS). It represents only the unconfined superficial and Leederville
aquifers with six model layers.
In northern Australia, the groundwater system in the Daly Basin contains three layers: an
upper sandy surface; the productive carbonate aquifers and an aquitard in the middle; and a
fractured-rock basement of siltstone, granite and volcanic rocks. Similarly, the Howard East
groundwater system contains an upper layer of laterite aquifer with the highest permeability
near the surface, grading down to a second layer comprising poorly weathered laterite and
sandy quartzy-weathered dolomite, with a third layer of fractured dolomite. The groundwater
models of these systems were therefore is constructed in three horizontal layers.
Three existing groundwater-flow models were available in Tasmania. In the Mella–Togari area
the dolomite and siltstone are simplified to two layers, the first r consisting of loose sediments
and basement outcrop areas, and the second combining dolomite, mudstone and siltstone.
Wesley Vale is dominated by layers of basalt, providing a water resource where it is fractured,
an aquitard where it is less fractured or heavily weathered and outcropping, and which is
interbedded with layers of sediments. The numerical model uses three layers: surface basalt,
a sand layer and deep basalt. The model design for the Scottsdale area is similar to the
models developed for the MDB aquifers: a distinct surface layer of highly weathered and clayrich basalt overlying thick sand, gravel and silt sequences forming the main productive
aquifer. The numerical model consists of these two layers.
Relationship to national aquifers characterisation
The aquifers studied as part of the various modelling tasks in previous work and reported in
this chapter do not directly correlate with those identified nationally as part of this climate
change impacts study.
Generally, the modelled areas of the MDB relate to two main priority aquifers—the Calivil and
the Gunnedah and, in a few cases, the Lachlan . The aquifers modelled in the northern
Australia study correlate directly to the Daly Basin aquifer and the Darwin region aquifer for
the Daly Basin model and the Howard East model, respectively. In Tasmania, the Mella–
Togari model is part of the Smithton Dolomite aquifer, the Wesley Vale model is part of the
Tasmanian Tertiary Basalts aquifer, and the Scottsdale model is part of the Tasmanian
Tertiary Sediments aquifer. The three Western Australian models cover the North, Central
and South Perth Basin aquifers.
Recharge and discharge processes
When the impacts of climate change on groundwater resources are considered, the
processes of recharge and discharge are likely to be most affected. Changes in groundwater
recharge under future climate scenarios were considered in Chapter 4, but the combined
effects of those changes on groundwater resources may only be assessed using groundwater
modelling. However, the conceptual modelling and model design may have a significant effect
on how groundwater models simulate the climate change impact on groundwater resources.
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The processes considered in the reviewed models included diffuse rainfall recharge, diffuse
irrigation recharge, leakage from rivers and water courses, flood recharge, and head and flux
boundary conditions. In general, diffuse rainfall recharge was applied as a temporal sequence
of a fraction of measured rainfall. In the reviewed models this fraction varied from more than
70 per cent in the case of a very permeable surface layer in sedimentary systems of Central
Perth to less than 1 per cent for areas with a thick surface-clay layer in alluvial systems such
as the Lower Namoi. Only two out of the reviewed models—PRAMS and SWAMS—used a
vertical flux model (VFM), which dynamically links estimation of diffuse recharge and diffuse
discharge and accounts for the depth to the groundwater table.
Irrigation and flood recharge were based on the known spatial extent of these seasonal
fluxes. The volumes and rates of any of these diffuse sources used in the models were
commonly selected, based on a combination of measurement, surrogate estimation, expert
knowledge and model fitting. River leakage is commonly modelled in a simplistic manner
using head difference between river stage and groundwater level. The magnitude of leakage
fluxes is most often arrived at in the process of model calibration. Head and flux boundary
conditions of a model domain may provide either a source or sink that can vary as the local
water level changes throughout the model simulation run. Head boundaries do not commonly
incorporate any considerations related to climate change impacts on boundary conditions.
The processes modelled that lead to a removal of water from the aquifer are groundwater
pumping, evaporation, river discharge and head and flux boundary conditions. Pumping is
often the major discharge mechanism for water from the exploited aquifers, but accurate
volumetric estimates of this flux in space and time are limited. The abstracted water can be
partly returned to the model if water is used for irrigation or to maintain stream stages, and
therefore can contribute to groundwater recharge. Evaporation from groundwater occurs
when levels become very shallow or close to the surface, where it can be intercepted by the
root system of surface vegetation or lost directly to evaporation. This is usually very
simplistically handled in models, or ignored when water levels are considered deep enough
not to interact with the surface. However, depths to groundwater are not commonly specified.
In the models with VFMs, plant-rooting depth is an available parameter, but in the models
reviewed here the roots are cut off 1.5m above the watertable.
Discharge to rivers can occur when the local groundwater level is higher than the river level.
As with river leakage, the fluxes are not well known and are usually determined as part of the
model calibration process. Dicharge to the ocean is commonly modelled as a flux at a model
boundary such as in PRAMS, SWAMS and the Tasmanian models. As with recharge
processes, head and flux boundary conditions may be either a source or sink of water, with
the direction and magnitude of the flux potentially varying over the simulation.
Review of model results
Modelling historical conditions
Groundwater modelling results for the MDB (CSIRO 2008a–f), northern Australia (CSIRO
2009b–d), south-west Western Australia (CSIRO 2009a) and Tasmania (Harrington et al.
2009) are available. The water-balance components for the model fits are shown in Figure 50
and Figure 51. The alluvial-type aquifers of the MDB are all shown on the left-hand side of
these figures and, with the exception of Lower Macquarie, these systems all show more than
half their total inputs are with localised (flood) recharge. The sedimentary type aquifers of
northern and Western Australia and Tasmania, on the right-hand side, all show diffuse inputs
as more than 60 per cent of their total water balance. This result is expected, as the alluvial
systems are configured with the lowest conductivity material at the surface, while the
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sedimentary systems have a high conductivity surface layer. PRAMS and SWAMS have
limited localised recharge mechanisms, with all water courses modelled as drains.
100
Percent
80
60
Diffuse
Localised
40
20
SWAMS
PHRAMS
PRAMS (super)
Scottsdale
Mella/Togari
Wesley Vale
Daly Basin
Howard East
SRP - Ovens
SRP - VIC
SRP - NSW
Low Murrumbidgee
Lower Lachlan
Mid Murrumbidgee
Upper Lachlan
Lower Macquarie
Upper Macquarie
Lower Namoi
Upper Namoi
Gwydir
Upper Condamine
0
Figure 50: Proportion of point localised and diffuse input components to groundwater models,
under fitted historical conditions
Inspecting Figure 51 with the model discharge components, the water balance in the MDB
alluvial systems is dominated by groundwater abstraction. This suggests that human activity
has a profound effect on the water levels and storage of these aquifers. The discharge fluxes
in the sedimentary systems are more mixed and largly dependent on the depth to
groundwater in the upper layers. For example, in the three Tasmanian models the
groundwater is very shallow, pumping is very low and the areas are extensively irrigated.
Primary discharge mechanisms in this system are to water courses, here noted as ‘river’, and
through direct evaporation from watertable. In the PRAMS and SWAMS models water losses
to evapotranspiration are not shown on the plot, but these fluxes are included in net recharge
estimation.
20
0
Boundary
Evaporation
River
-40
Pumping
-60
-80
SWAMS
PHRAMS
PRAMS (super)
Scottsdale
Wesley Vale
Mella/Togari
Howard East
Daly
SRP - Ovens
SRP - VIC
SRP - NSW
Mid Murrumbidgee
Low Murrumbidgee
Lower Lachlan
Upper Lachlan
Lower Macquarie
Upper Macquarie
Lower Namoi
Upper Namoi
Gwydir
-100
Upper Condamine
Percent
-20
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Figure 51: Proportion of discharge components from groundwater models under fitted
historical conditions. Negative values are a net discharge flux, positive values are a net gain
to the system.
In the PRAMS and SWAMS models, losses to the ocean occur in more than half of the total
model boundary, so this condition dominates their water balance. Note that in some cases the
flux from all boundary conditions provides a net influx of water, and thus will appear as a
positive value in the graph.
Modelling future scenarios
All groundwater models were run with a variety of future climate scenarios. Of these, the
water-balance components will be presented only for those common to all reported results: a
median future scenario and a dry future climate scenario. The values for alluvial and
sedimentary systems are shown separately.
Figure 52 shows the changes in water-balance components, both recharge and discharge, for
the alluvial aquifers of the MDB under a median future climate. In this scenario rainfall
recharge is projected to reduce or remain similar to historical levels (Crosbie et al. 2010c)
across the MDB. In the case of each of the modelled systems there is a projected systematic
reduction in diffuse recharge as a result of rainfall and flooding, such as up to 25 per cent in
the Lower Lachlan. The smallest reduction is likely to be in the Lower Macquarie, which is
projected to have the highest proportion of diffuse recharge in Figure 50. The direction of
change in localised recharge from river leakage is mixed across the models, but is relatively
small in magnitude
(from +5 per cent to –8 per cent). Since the changes in river stage under the future climate
scenarios were not incorporated in the models, projected changes in river leakage are due to
changes in the depth to watertable.
Projected changes in discharge are shown in Figure 52(b). The relative changes are likely to
be of the same order as the recharge changes already shown, and are quite varied in their
direction from model to model. The apparently large relative changes to boundary fluxes in
the Upper Namoi do not lead to large changes in modelled volumes because of very small
boundery fluxes under the historical climate. Evaporation and river discharge are generally
projected to fall, which reflects a general lowering of water levels due to reduced recharge.
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50
(a)
Diffuse
Localised
Percent
25
0
-25
-50
50
(b)
Boundary
Evaporation
25
River
Percent
Pumping
0
-25
SRP - Ovens
SRP - VIC
SRP - NSW
Low Murrumbidgee
Mid Murrumbidgee
Lower Lachlan
Upper Lachlan
Lower Macquarie
Upper Macquarie
Lower Namoi
Upper Namoi
Gwydir
Upper Condamine
-50
Figure 52: Percentage change in a) recharge and b) discharge water-balance components for
alluvial aquifers of the MDB under a median future climate. All changes are relative to the
absolute fitted values from the historical simulation.
Figure 53 shows the recharge and discharge components for the sedimentary systems.
Future climate conditions from GCMs project rainfall to be similar or greater than historical
across northern Australia, resulting in a modest increase in diffuse recharge in Daly Basin and
Howard East. Similarly, all GCMs simulate a decrease in annual rainfall across the south-west
of Western Australia, which results in a strong modelled decline in diffuse recharge.
The discharge components in Figure 53(b) again reflect the ambient groundwater levels of
each area. For the Northen Territory and Tasmanian aquifers there is very little change in
discharge projected. This is likely to be due to a projected increase in rainfall, shallow
watertables, and ocean discharge as a boundary condition that provides overall stability in
water balance. In the case of Tasmania there is also relatively little groundwater extraction.
The Western Australian cases show a consistent reduction in discharge components of the
model water balance as a result of generally lower groundwater levels due to consistent
reduction in rainfall projected for this region. In PRAMS and SWAMS only net groundwater
recharge is calculated, so there is no separately reported change in ‘evaporation’ even if it
does occur.
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50
(a)
Diffuse
Localised
Percent
25
0
-25
-50
50
(b)
Boundary
Evaporation
25
River
Percent
Pumping
0
SWAMS
PHRAMS
PRAMS (super)
Scottsdale
Wesley Vale
Mella/Togari
Howard East
-50
Daly
-25
Figure 53: Percentage change in a) recharge and b) discharge water-balance components for
sedimentary aquifers of NT, WA and Tasmania under a median future climate. All changes
are relative to the absolute fitted values from the historical simulation.
Figure 54(a) and Figure 54(b) present the projected relative change in the recharge and
discharge components, respectively, for the various modelled alluvial aquifers under a future
dry climate.
Figure 54(a) shows that with a dry future there is a likely reduction in diffuse recharge across
the MDB. Some aquifers show an increase in localised recharge due to a reduction in
watertable with no modelled changes in river stages. These increases are a result of using
fixed riverhead conditions that allow water to freely enter and leave the model domain. As
modelled groundwater heads become lower due to less recharge, the head difference with
the boundary increases and thus more water is estimated as entering the model domain.
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50
(a)
Diffuse
Localised
Percent
25
0
-25
-50
50
(b)
Boundary
Evap
25
River
Percent
Pumping
0
-25
SRP - Ovens
SRP - VIC
SRP - NSW
Low Murrumbidgee
Mid Murrumbidgee
Lower Lachlan
Upper Lachlan
Lower Macquarie
Upper Macquarie
Lower Namoi
Upper Namoi
Gwydir
Upper Condamine
-50
Figure 54: Percentage change in a) recharge and b) discharge in the water balance for
alluvial aquifers of the MDB under a dry future climate. All changes are relative to the
absolute fitted values from the historical simulation.
The discharge components in Figure 54(b) tell a similar story. River discharge and direct
evaporation are projected to uniformly decrease as local groundwater levels fall. In one case
(SRP–Vic) pumping has decreased as a result of localised drying out of an aquifer from overextraction. The direction of fluxes associated with boundary conditions continue to be mixed.
Extreme values of boundary-flux changes for the Upper Namoi are again a result of very
small historical fluxes, and the changes indicated are insignificant in terms of the overall water
balance.
Projected changes in inputs to the sedimentary aquifers under a dry future climate are shown
in Figure 55(a). Most of the input fluxes are lower than under the median future climate, with
SWAMS experiencing the largest drop in diffuse net recharge of –56 per cent. The modelled
discharge components in Figure 55(b) show that projected changes in the Northen Territory
and Tasmanian aquifers are of the order 10 per cent. These changes are projected to be of
a similar scale to changes in inputs as in Figure 55(a).
For the Western Australian models, however, the changes are projected to be much larger,
which may reflect the lowering watertable due to the consistent and strongly downward future
projection of annual rainfall, which caused a substantial reduction in discharge to rivers and
the ocean.
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50
(a)
Diffuse
Localised
Percent
25
0
-25
-50
50
(b)
Boundary
Evaporation
25
River
Percent
Pumping
0
SWAMS
PHRAMS
PRAMS (super)
Scottsdale
Wesley Vale
Mella/Togari
Howard East
-50
Daly
-25
Figure 55: Percentage change in a) recharge and b) discharge input water balance
components for sedimentary aquifers of NT, WA and Tasmania under a dry future climate. All
changes are relative to the absolute fitted values from the historical simulation.
Effect of climate change on groundwater
resource
The Australian Natural Resources Atlas (DEWHA 2009) uses a working definition of
‘sustainable water provision’, namely the limit on potentially divertible water that will be
allowed to be diverted from a resource after taking account of environmental values and
making provision for environmental water needs. Further, a working definition of ‘sustainable
yield’ was developed and is the groundwater extraction regime, measured over a specified
planning timeframe, that allows acceptable levels of stress and protects the higher value uses
that have a dependency on the water. The NWC (AWR 2005) used the Intergovernmental
Agreement on a National Water Initiative for a definition of ‘environmentally sustainable level
of extraction’ as the level of water extraction from a particular system that would compromise
key environmental assets, or ecosystem functions and the productive base of the resource, if
it were exceeded.
The following quote from the Australian Natural Resources Atlas (DEWHA 2009) summarises
the main method of estimating sustainable yield, and the major problem with using a broad
definition:
Considerable ongoing effort will be required to operationalise the concept [of
sustainable yield] and review its implementation. Nonetheless the States have used a
broad range of approaches to calculate sustainable yield: the principal method being
a percentage of the assessed rainfall (commonly between 1 per cent and 5 per cent)
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as being the recharge and all or the majority of the recharge being the sustainable
yield. However, in many cases other hydrogeological criteria and approaches have
been adopted to suit specific circumstances.
The agreed national definition acknowledges that 'storage depletion' may occur. The
approach provides a requirement for intervention when extraction levels cause
unacceptable impacts such as storage depletion. The extent to which this has been
applied is not clear. Nonetheless considerable scope exists for widely differing
approaches between the States, with the result that it is not easy to compare across
Australia.
It is the broad definition of sustainable yield and variation in estimation and time frame across
Australia that makes consistent comparison of work impossible. Inherent in the time frame
and measurement of groundwater levels is the local definition of the ‘groundwater resource’.
In the MBDA work, for example, bore extraction was modified under current and future
climate regimes so that four criteria were met:

stabilisation of groundwater levels: levels must be stable (annually) or rising at key sites
after 50 years

stabilisation of extraction: pumping rates must be maintained at the full rate, i.e. not cause
any model cells to dry out, for 50 years

prevention of dewatering confined aquifers: levels must remain above the upper level of
confined aquifers at key sites for 50 years

maintenance of current environmental river flows: the sustainable limit must be less than
the current actual level of extraction, averaged over the previous five years.
In these model results, storage depletion was a small part of the water balance, thus the
implicit definition of groundwater resource is tied to the amount of recharge (mostly climate
controlled) and discharge (mostly human controlled). All reductions in recharge must be
matched with reductions in extraction of river flow. In the MDBA results, nine of the 13 models
required a reduction in pumping to meet the criteria for a median and dry future climate. The
average reduction was –24 per cent of current pumping, and five models required a further
average drop of –41 per cent to meet all criteria. These reductions can be compared with the
average recharge reduction of –14 per cent for median and –29 per cent for dry future
climate. Under the current pumping regime and historical climate, two of the models violated
one or more of the sustainability criteria.
In the MDBA work, the groundwater resource is implicitly defined by the amount of recharge,
where the dryland component is almost exclusively a simple percentage of rainfall. All
projected changes in annual rainfall as a result of climate change translates proportionally into
recharge, and therefore the groundwater resource. This is a flawed and over-optimistic
implementation, as rainfall-recharge elasticity shows that there is a greater percentage
reduction in recharge for a given percentage reduction in rainfall. This modelling estimates the
reduction in bore extraction required to maintain the resource as defined.
The models reviewed in the Northern Territory, Tasmania and Western Australia were run
under future climate and (generally increasing) pumping scenarios, with storage and
discharge changes described as a result. Here the groundwater resource is defined by the
amount of storage and the changes modelled as a result of climate and direct human
changes, e.g. pumping and land cover. In these cases all changes in recharge and increases
in pumping are met by changes in storage or discharge water balance components, e.g.
evaporation or drain discharge.
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The Northern Territory and Tasmania are simple cases where median future rainfall is similar
to current amounts or greater, and current levels of pumping are sustainable in terms of
stable water levels and storage volume. While there is little planned expansion of bore
extraction in Tasmania, increasing it to a level of
25 per cent of estimated recharge as a modelling experiment showed that these levels
caused local drying out without substantially affecting the rest of the model domain. Increased
pumping was therefore not sustainable.
The model results in Western Australia are more interesting. In the PRAMS area there is a
general decline in total rainfall, but recent and planned land-cover changes have a significant
effect on recharge and storage. On the Dandaragan Plateau north-east of Perth, where
clearing of native vegetation for cropping and grazing has occurred for over 50 years or more,
long-term water levels have been steadily rising. This pattern is expected to continue into the
future with an average modelled rise of 5.4 m to 2030 under a median future climate, and a
3.3 m rise to 2030 under a dry future climate. In the coastal zones north and south of Perth,
average groundwater levels change by 1 m to 2030 under the median and dry futures, and it
is beyond the accuracy of a regional model to say more than that the levels are probably
stable. This result comes as rainfall reduces by –7 to –17 per cent; land-cover change to the
north, however, replaces pine forest with native regrowth and, as some water levels drop, the
areas stop discharging through evaporation or to drains. The PRAMS area increases its
storage under both median and dry future climates, but while historical conditions have
allowed 23 per cent of recharge to increase storage, under a median climate 17 per cent of
recharge increases storage, and under a dry climate only 4 per cent does.
In the models described above, the groundwater resource is described by changes to storage
or water levels as a result of climate changes on a system where extraction is constant or
increasing. The resource condition can be assessed in similar terms to the previous section,
i.e. water-level behaviour at key indicator sites, status of confined aquifers, or volume of
discharge to rivers and drains. While water levels remain above some critical trigger levels,
this type of resource definition allows a timescale to be modelled that indicates how long the
system can be sustained with the current regime of extraction under any future climate.
Discussion
Groundwater flow within aquifers is linked to climate and anthropogenic changes through the
latter’s effect on the recharge and discharge processes. Modelling undertaken in the reviewed
studies indicates that for sedimentary aquifers with a relatively permeable layer at the surface,
the direct effects of changes in rainfall and evaporation play a significant role. In these cases
the diffuse fluxes are directly affected by the magnitude of change in rainfall in a future
climate. For example, an area where annual rainfall is projected to decrease can expect, a
priori, a decrease in recharge. For these areas a sensitivity to climate change could be
derived from estimates of likelihood of future rainfall and evaporation changes.
For the modelled alluvial systems, the surface layer is relatively less conductive than the
deeper strata, and will confine the main water-bearing aquifer. In these models the main
components of the water balance are fluxes to and from a river, and the boundary conditions.
The water transfers between a river and local groundwater are controlled by the river stage,
which in turn is affected by rainfall-runoff behaviour in a future climate. For regulated rivers,
maintaining stage and supply to customers in a future with less rainfall may become more
difficult. Groundwater pumping is the major discharge for many of these systems and, like
river regulation, is entirely anthropogenic in nature. Sensitivity to climate in these aquifers, as
modelled, is a result of flow-on effects of climate changes. That is, a reduction in rainfall may
lead to less water-filling storages, which in turn leads to reduced river stage or water security,
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which leads to less river leakage and more groundwater pumping. Climate sensitivity
becomes a function of commercial and economic factors.
Modelling climate change with groundwater models
The outcome of models is limited primarily by our own understanding of the hydrogeological
conditions and, secondarily, by specific model implementation and operation.
Computer models are necessarily conceptual simplifications of reality based on limited
observation and groundwater- system understanding. This is the case both in conceptualising
the model domain and in estimating and distributing the various hydrogeological properties,
recharge and discharge fluxes, and fluxes associated with boundary conditions. In
groundwater modelling this is most true as an extensive three-dimensional underground
structure is sampled by, and interpreted with, a series of pinprick holes and point estimates.
This is an inherent but seldom explored limitation.
The secondary limitation is the models themselves. If only a subset of the processes is
considered, then some questions cannot be answered. The most common groundwater
models are well suited to incorporate the direct effects of climate change such as changes to
inputs like rainfall recharge, or anthropogenic alterations such as reducing pumping volumes.
The weakest link is indirect changes, such as those associated with river stage and combined
groundwater and surface water-supply management. It is rare in groundwater modelling to
incorporate river stage within a groundwater model based on its relationship with rainfall
runoff and flow routing. It is computationally intensive and creates very large input datasets to
dynamically alter flow regimes, with the additional consideration of flooding. Where an area is
large and there is enough detailed information, transient data on diffuse sources such as
rainfall recharge can also be very large and cumbersome, often requiring additional external
computation to assemble the necessary data.
As a corollary to the limitations of the models themselves, the operation of the models is also
important. A groundwater model can reproduce the modelled process as it is defined within
the model, based on the conceptual understanding of their magnitude and spatial and
temporal occurrence. However, the conceptualisation of the hydrogeological systems may
vary largely, depending on judgment of the model developers. For example, a groundwater
model based on the assumption that diffuse recharge is to be ‘net’ recharge (after all vertical
losses are removed) will appear to perform poorly when given ‘gross’ recharge (for instance,
recharge that does not account for some evaporation that would otherwise have been
removed) instead.
Similarly, a priori knowledge is required when generating model inputs, which is particularly
relevant to recharge estimation under future climate scenarios. From the simplistic model
input describing net recharge as a fixed percentage of total rainfall, a 10 per cent decrease in
future rainfall would be translated to a matching 10 per cent decrease in net recharge.
However, if we know a priori that the elasticity in the process means that a 10 per cent
decrease in annual rainfall leads to a 20 per cent decrease in net recharge, then the simplistic
translation of a 10 per cent decrease would underestimate the impact on recharge. That
simulation by the model would be a poor estimate of the future groundwater levels and
groundwater resource as the groundwater model did exactly as it was asked but with the
wrong assumptions related to net recharge estimation.
Some care must be taken with pumping when an aquifer layer is thick, since models will
generally assume that extraction takes place from the middle of the layer. Where wells are
extracting from very different parts of a layer, sublayers may need to be considered for the
most accurate representation. This is done, for example, for the Leederville and Yarragadee
aquifers in the PRAMS model where each of these single aquifers has three model layers.
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Failure to do so can lead to a model drying out an aquifer layer and falsely implying that
pumping is not sustainable, or drawdown is very large. Flood and irrigation recharge is usually
handled via the diffuse recharge mechanism (used for rainfall or net recharge), but is
completely dependent on the model operator in terms of their spatial and temporal patterns.
Processes that are less well handled, or more subjective and therefore dependent on the
operator, are evaporation losses and boundary conditions. Evaporation losses are often
linked with net recharge modelling, where an operator generates a spatial map that
convolutes surface soil type or geology with vegetation cover, for example. The logic behind
this is clear when net recharge below trees is very different to that below grasses or bare
ground. The mechanism for extracting groundwater by evaporation, when modelled in
addition to net or gross recharge, generally specifies a maximum rate at the surface with a
linear decrease to an extinction depth. Knowing this is the process description, an operator
can accommodate variations according to any scheme that generates a spatial map, for
example a soil or land-use map.
Boundary conditions define the fluxes at the boundaries of the modelling domain and can be
a source or sink for water. Where possible, no-flow boundary conditions are likely to provide
the least effect on the model fluxes as these are least likely to change and do not contribute a
flux to the model.
Processes that are not handled well are associated with fluxes from and to rivers and include
both the river stage and river exchanges with groundwater. River stage can be highly dynamic
and not on the same timescale as groundwater movement, yet a long stress period in a
groundwater model implies that river stage in a computational cell is constant for the entire
stress period—one month for example. If a river is not regulated this is unlikely, which leads
to errors in estimating stream and groundwater-exchange fluxes. It also implies that the river
is an infinite source of, or sink for, water.
Estimating the flux between the river and groundwater is commonly further simplified. The
fluxes generally follow a linear function of the head difference between the river and local
groundwater, moderated by a conductance value. The streambed conductance is often
derived from model fitting, and thus is used as an input parameter to compensate for the
errors in process representation. Other research (Brunner et al. 2009, 2010) indicates that the
response to head change is linear within a range of head difference but thereafter becomes
non-linear. If the head difference becomes large enough, hydraulic disconnection between
river and groundwater can occur and recharge from the river is no longer defined by Darcy
flow, as the flow is unsaturated. The flux in such conditions becomes constant. This clearly
has implications for modelling the effect of changing stream stage due to decreased runoff or
changing management rules in a regulated stream. An additional limitation is related to the
misrepresentation of the effective river width, which in many low-valley rivers is the
dominating factor in localised recharge changes under changing flow conditions.
Models such as MODFLOW were designed more than 20 years ago and have undergone
long and meaningful changes over time. While there is considerable effort in improving
computational efficiency and numerical convergence, much more effort has gone into user
interfaces designed simply to assemble the necessary input files. Being a very old system,
too, the input files are few, and are designed to be open for an entire simulation and read
sequentially. It is this structure that leads to massive input files that are unique for each run.
It is possible to modify and recompile the open-source models to include any number of new
processes, input and output variations, etc. This is a non-trivial exercise requiring a detailed
understanding of computer programming and numerical modelling to implement.
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A modern groundwater simulator should have an integration of surface water processes
leading to changes in river stage and flux. Where flooding is an important process, it must be
handled within the same framework. The input structure must provide more flexibility for
dynamic and transient data inputs, specifically not requiring a single file to describe one flux
for each stress period for an entire simulation, for example.
Process-based coupled surface water–groundwater models appear to be most suitable for
simulating such conditions. Recently, a number of models have become available to simulate
fully coupled surface water–groundwater systems: the European MIKE SHE (DHI Water &
Environment 2007), and from North America InHM (VanderKwaak 1999), MODHMS
(Hydrogeologic Inc. 2006), MODFLOW WHaT (Thoms 2003), HydroGeoSphere (Therrien et
al. 2005), and more recently GSFLOW (Markstrom et al. 2008). Being process-based, such
models are also suitable for modelling of land-cover changes (Barron and Barr 2009).
However, the reported application of these models has been restricted to small catchments
(Maneta et al. 2008) or topographically diverse catchments (Jones et al. 2008). Werner and
Gallagher (2006) used a multilayer MODHMS model with density dependence to investigate
the seawater intrusion into the Pioneer Creek catchment in Queensland, which includes an
ephemeral channel network and a number of wetlands.
The challenge in using these physically based distributed coupled surface water–groundwater
model is the large data requirement. Each individual process (e.g. channel flow, overland
flow, unsaturated zone and saturated flows), requires a specific set of parameters that have to
be distributed over the model domain. The coupling of surface water and subsurface water
processes is also computationally expensive as the spatial and temporal scales for the
individual components are different, requiring either simulation of all processes at the smallest
relevant scale (fully coupled) or of each component individually, and subsequently integrating
them (iterative).
Conclusions
Groundwater resources in the reviewed modelling were defined differently. In the MDBA
studies, the groundwater resource was an amount of groundwater that could be abstracted
without changes in groundwater storage. In other models the change in storage was a
measure of climate impact on resources. The results of this review can be summarised as
follows:

‘Groundwater resource’ can be defined as the volume of water that can be removed from
the system for no change in total storage, or with some defined level of storage depletion.

Prior knowledge of the relationship and elasticity between rainfall and recharge is required
to implement climate change in a groundwater model where it is represented as a fixed
fraction of total rainfall.

Prior knowledge of the effects of climate change on runoff in regulated and unregulated
rivers is required to appropriately describe the river stage in groundwater models.

In the MDBA models, pumping rates were left the same as historical levels or reduced as
required to maintain groundwater levels at keys sites. All reductions in recharge were
compensated for by reducing pumping, yet none of the models was considered sensitive to
climate change.

In the Northern Territory and Tasmanian groundwater models, local groundwater levels
were stable under current pumping regimes and, with little future expansion of pumping
planned, also considered sustainable.
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
In groundwater models in Western Australia, current pumping levels were maintained, and
a consistent downward trend in future rainfall leads to a decreasing amount of water being
stored. In the south-west there was a change from net storage to net loss of groundwater
from the current climate to a future dry climate.

The use of an appropriate model is critical for being able to answer questions about the
impact of change to groundwater systems. The biggest impediment is linking surface and
groundwater processes appropriately, and then populating the model with all the
necessary data.
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5. Climate change impacts on
groundwater resources, environment,
agriculture and water supply in key
aquifers of Australia
This chapter aims to summarise the results of the project work for the 14 high-priority aquifers
indentified in Chapter 3 and Currie et al. (2011). The names of individual aquifers grouped
within each priority aquifer are given in Appendix 2. A brief description of the priority aquifers
is provided, including the climate type in which each aquifer is located, an overview of the
hydrogeology, recharge mechanisms, main soil types and land use. Historical and projected
future rainfall under three future climates considering three global warming scenarios and 16
GCMs is outlined next. This is then followed by the description of changes in projected diffuse
recharge estimated by modelling (as in Chapter 4 and Crosbie et al. 2011a). The impacts on
agriculture, water supply, commercial and mining industries and the environment due to
projected changes in diffuse and localised recharge are given in the last section of this
chapter. This section also describes the likely impacts on surface water–groundwater
interactions and GDEs from projected changes in diffuse and localised recharge.
High-priority aquifers—brief description
Fourteen aquifers were identified as high-priority based on their importance and sensitivity, as
described in Chapter 3 and shown in Figure 56. A brief description of each is given below.
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Figure 56: Map showing the location of high-priority aquifers
Lachlan
The Lachlan aquifer occurs within two climate types. About 45 per cent of its area lies within
the arid climate type (BSk) and 55 per cent in the equiseasonal–hot climate (Cfa) (Table 8). It
includes the Billabong Creek, Mid-Murrumbidgee, Upper Lachlan and Upper Murray Alluvial
GMUs on the western slopes of the Great Dividing Range in southern New South Wales.
Each of these areas is characterised by relatively deep valleys containing alluvial deposits
associated with the current and ancient drainage systems.
The main productive aquifer is the confined Lachlan Formation, a Late Tertiary alluvium up to
80 m thick and comprising well-sorted, clean quartz sand and gravel (CSIRO/SKM 2010; BRS
2008). Groundwater is predominantly fresh (150–950 µS/cm EC) but decreases in quality
away from the current surface water drainage systems (CSIRO/SKM 2010).
Overlying the Lachlan Formation is the Quaternary Cowra Formation (contemporaneous with
the Shepparton Formation), which comprises unconsolidated gravels, silts and clays with
shoestring sand lends. The Cowra Formation ranges in thickness from 35 to 80 m
(CSIRO/SKM 2010). Groundwater in the Cowra Formation,
at >1000 µS/cm EC, is typically of poorer quality than in the Lachlan, but extraction,
predominantly from the underlying Lachlan Formation, has resulted in significant drawdown
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and dewatering of this unit (BRS, 2008). Localised recharge is the main recharge process.
Diffuse recharge also occurs through seasonal rainfall.
The main soil types in the aquifer area include relatively less permeable (hydraulic
4
conductivity less than
0.5 m/day) Sodosols (duplex soils characterised by red-brown earths and desert loams) in
about 68 per cent of the area and more conductive (hydraulic conductivity >1 m/day)
Kandosols (red, yellow and grey earths and calcareous earths) in about 14 per cent (
4
All soil conductivity values are given as a weighted hydraulic conductivity over 4 m soil profile as defined in Chapter
4.
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Table 9). Predominant land use is dryland agriculture. Irrigated agriculture and plantations
occupy about 2.2 and 1.2 per cent of the area, respectively (Table 10). Extraction from
Lachlan Formation aquifers is high, with groundwater used extensively for town water supply
and irrigation purposes. As a result, substantial drawdown (up to 20 m) is observed at many
locations (CSIRO/SKM 2010).
Newer Volcanics
Most of the Newer Volcanics aquifer area lies within the equiseasonal–warm climate type
(Cfb). Only about 13 per cent lies within the winter rainfall climate (Csb) (Table 8). These are
basalt aquifers that form in broad, low volcanic plateaus throughout western Victoria.
Fractures in the basalt form the primary pathways for groundwater flow. The aquifers are
recharged directly through numerous volcanic cones and via infiltration through fractures.
Recharge occurs preferentially in areas of less-weathered basalt, stony rises and eruption
points. Outside of preferential recharge areas, a lower flux of water reaches the watertable
because of lower infiltration rates and increased evapotranspiration (Tweed et al. 2007).
Groundwater flow typically radiates outward from the elevated recharge sources into the
plains. Groundwater quality of the Newer Volcanic aquifers is highly variable depending on
proximity to the recharge area. Groundwater is of good quality (<560 mg/L total dissolved
solids (TDS)) around volcanic vents and increases to over 3360 mg/L TDS in low-recharge
areas. Groundwater quality of the basalt in the Daylesford area is good, averaging around
200 mg/L TDS (Heislers 1993).
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Table 8: Different climate types in the high-priority aquifers shown as per cent of the total
aquifer area
Aquifer
Lachlan
Total
area
2
(km )
Per cent (%) of aquifer area
(1) Tropics*
(2) Arid
(3) Winter rainfall
(4) Equi­
seasonal–
hot
(5) Equi­
seasonal–
warm
15 523
0
45
0
55
0
3 369
0
0
13
0
87
12 085
0
0
0
100
0
677
67
0
5
29
0
Coastal River Alluvium
1
3 677
99
0
0
1
0
Toowoomba Basalts
4 459
0
0
0
86
14
19 213
0
28
0
72
0
213 159
0
100
0
0
0
Port Campbell
Limestone
5 126
0
0
58
0
42
Coastal River Alluvium
4
7 315
29
0
0
69
2
Coastal Sands 4
2 901
0
0
0
98
2
Otway Basin
15 811
0
0
100
0
0
Adelaide Geosyncline
3
16 350
0
35
57
3
5
127 020
65
35
0
0
0
Newer Volcanics
Upper Condamine and
Border Rivers Alluvium
Atherton Tablelands
Gunnedah
Pilbara
Daly Basin
* Climate types included in climate zones are: 1) Tropics = Aw; 2) Arid = Bwh/BWk, BSh/BSk; 3) Winter
rainfall = Csa/Csb; (4) Equiseasonal–hot = Cfa; 5) Equiseasonal–warm = Cfb, Cfc, Dfb, Dfc.
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Table 9: Main soil types in the high-priority aquifers shown as per cent of the total aquifer area
(Johnston, et al. 2003)
Hydrosol
Kurosol
Sodosol
Chromosol
Calcarosol
Ferrosol
Dermosol
Kandosol
Rudosol
Tenosol
Lake
Lachlan
0
0
7
0
0
68
7
0
0
2
14
1
0
1
Newer Volcanics
0
1
3
0
0
61
11
0
0
13
1
1
6
3
Upper Condamine and
Border Rivers Alluvium
0
0
59
0
1
29
3
0
0
5
0
1
1
0
Atherton Tablelands
0
0
0
0
0
0
0
0
63
20
0
0
13
4
Coastal River Alluvium 1
2
0
5
4
1
44
7
0
0
24
11
0
3
0
Toowoomba Basalts
0
0
65
0
0
4
4
0
5
0
0
0
22
0
Gunnedah
0
0
69
0
0
22
2
0
1
3
3
0
0
0
Pilbara
0
0
4
0
0
26
3
4
0
0
18
1
45
0
Port Campbell Limestone
0
36
0
0
0
24
19
0
0
4
0
6
11
0
Coastal River Alluvium 4
0
1
7
9
13
24
7
0
3
25
6
0
3
0
Coastal Sands 4
0
28
0
37
11
4
1
0
1
9
1
2
6
1
Otway Basin
0
8
18
0
0
51
1
0
0
2
0
1
17
2
Adelaide Geosyncline 3
0
1
1
2
11
10
59
11
0
0
0
0
5
0
Daly Basin
0
0
5
1
2
1
2
0
1
0
42
15
31
0
Organosol
Vertosol
Per cent of aquifer area (%)
Podosol
Aquifer
Table 10: Main land uses in the high-priority aquifers shown as per cent of total aquifer area
Aquifer
Per cent of total area (%)
Dryland
agriculture
Irrigated
agriculture
Nature
conser­
vation
Plantation
Residential/
infra-structure
Mining
Lachlan
94.3
2.2
0.6
1.2
0.3
0.0
1.4
Newer
Volcanics
84.2
1.5
3.5
5.7
2.3
0.0
2.7
Upper
Condamine and
Border Rivers
Alluvium
89.2
6.0
0.9
3.1
0.6
0.0
0.2
Atherton
Tablelands
49.2
7.3
9.5
25.2
3.8
0.0
5.0
Coastal River
Alluvium 1
48.9
19.3
20.0
2.6
2.6
0.0
6.6
Toowoomba
81.7
4.1
8.3
2.8
3.1
0.0
0.0
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Basalts
Gunnedah
86.4
10.5
2.0
0.4
0.6
0.0
0.1
Pilbara
68.4
0.0
29.8
0.1
0.0
0.0
1.7
Port Campbell
Limestone
60.8
1.0
12.5
24.7
0.5
0.0
0.4
Coastal River
Alluvium 4
63.9
9.4
15.8
4.8
3.0
0.0
3.2
Coastal Sands
4
34.0
2.4
45.5
4.4
6.9
0.0
6.8
Otway Basin
80.2
3.5
3.6
9.9
0.5
0.0
2.2
Adelaide
Geosyncline 3
85.2
2.3
2.7
2.1
7.0
0.0
0.7
Daly Basin
65.7
0.1
33.6
0.0
0.2
0.0
0.5
About 61 per cent of the aquifer area has relatively low permeability duplex-type red-brown
earths (Sodosols) (Table 9). Prairie soils, chocolate soils, some red and yellow podzolic soils
(Dermosols) occur in about 13 per cent and non-calcic brown soils, some red-brown earths
and a range of podzolic soils (Chromosols) occur in about 11 per cent of the area. These are
medium to high permeability soils with hydraulic conductivities ranging from 0.6 to 1.2 m/day.
About 84 per cent of the area has dryland agriculture. Irrigated agriculture, native vegetation
and plantations use 1.5, 3.5 and 5.7 per cent of the area, respectively (Table 10).
Groundwater from these basalts is used for stock and domestic purposes, irrigation, and town
water supply.
Upper Condamine and Border Rivers Alluvium
The entire Upper Condamine and Border Rivers Alluvium aquifer area lies within the
equiseasonal–hot climate type (Cfa). The Border Rivers Alluvium (Queensland and New
South Wales) and Upper Condamine Rivers Alluvium (Queensland) are located on the border
of New South Wales and Queensland, and to the north of the border on the western slopes of
the Great Dividing Range.
The alluvial units are associated with the current drainage system and aquifers range from 10
m thick in headwater regions to greater than 120 m in the central areas of the river valleys
(DERM 2009; Barret 2009; CSIRO 2007). In both GMUs, groundwater is predominantly fresh
to brackish (<3000 mg/L TDS) and watertables are intersected two to 20 m below surface
(DEWHA 2009). Localised areas of more saline groundwater (3000 to 14 000 mg/L TDS) are
found in the northern and western portions of the Upper Condamine Alluvium GMU, while the
river is a source of localised discharge in lower reaches (CSIRO/SKM 2010).
Recharge to these alluvial aquifers occurs via diffuse rainfall recharge, inundation (flood)
recharge and river leakage. In the Upper Condamine Alluvium GMU groundwater discharge
to the Condamine River also occurs (CSIRO/SKM 2010).
The main soil types include relatively low-permeability black earths and grey, brown and red
clays (Vertosols) in 59 per cent of the area, and low conductivity red-brown earths and desert
loams (Sodosols) in about 29 per cent (
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Table 9). Dryland agriculture is the dominant land use (89 per cent), followed by irrigated
agriculture (6 per cent). Just over 3 per cent of the area has pine plantations (Table 10).
Atherton Tablelands
Two climate types occur in this aquifer area; 67 per cent lies within the tropics climate (Cwa)
and 29 per cent in the equiseasonal–hot climate (Cfa) (Table 8). The Atherton Tablelands are
located on the eastern slopes and tablelands of the Great Dividing Range in Far North
Queensland and comprise the Pleistocene Basalt aquifers of the Atherton A and B GMUs.
This aquifer comprises numerous, multilayered basalt flows separated by palaeo-weathering
surfaces and minor alluvial gravels of palaeo-drainage channels (Locsey 2004). Basalt-flow
thicknesses range from 50 to 120 m. However, groundwater is extracted primarily from the
fractured and thinner weathered zones of basalt. Pumping rates range from 2 to 20 L/sec up
to 40 L/sec (DEWHA 2009; CSIRO 2001).
The Quaternary Basalts are a highly dynamic system, characterised by horizontal flow rates
approaching 10 m/year and short groundwater residence times—mostly less than 30 years
(CSIRO 2001). Recharge is relatively high at 150 to 660 mm/year (or 16 to 33 per cent of
incident precipitation) but highly seasonal, coinciding with the summer monsoon season
(CSIRO 2001). Diffuse rainfall infiltration is the primary recharge mechanism, but only occurs
after the soil profile is fully wetted, usually by December of each year (AGE 2007). Minor
recharge also occurs via stream leakage (AGE 2007). The groundwater system is highly
connected to the surface water drainage system and most recharge that is not extracted
discharges to streams (CSIRO 2001). As such, the aquifers are considered a seasonally finite
resource (Balston and Turton 2006).
The basalts are considered to be highly developed and extracted groundwater is primarily
used for irrigation, town and industrial supply, and stock and domestic applications. Extraction
has increased by over an order of magnitude from approximately 3 GL/year in the mid-1980s
to 14 GL/year (approaching the then sustainable yield of 15 GL/year) in 2001 (CSIRO 2001).
The sustainable yield has since been increased. However, the system remains currently
overallocated and approaching extraction limits (DEWHA 2009). Despite this, groundwater
levels are stable and entitlements were 100 per cent of allocations in 2009–10 (DERM 2009).
About 63 per cent of the aquifer area is covered with chocolate soils (Ferrosols), about 20 per
cent with prairie soils, chocolate soils, some red and yellow podzolic soils (Dermosols) and
about 13 per cent ,with siliceous and earthy sands, alpine humus soils and some alluvial
loams (Tenosols) (
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Table 9). All are highly conductive soils with hydraulic conductivities ranging from 1 to 3.2
m/day. Two main land uses in the area include dryland agriculture (49 per cent) and pine
plantations (25 per cent). Irrigated agriculture and native vegetation occupy about 7 and 10
per cent of the area, respectively (Table 10).
Coastal River Alluvium 1
Almost all of the Coastal River Alluvium 1 aquifer area lies within the tropics climate type (Af,
Am, Aw) (Table 8). The Coastal River Alluvium 1 grouping incorporates the alluvial (fluvial)
aquifers on the tropical north-east coast of Queensland. The respective GMUs are moderately
2
sized (113 to 1340 km ).Three of the larger GMUs in this grouping (the Burdekin River Delta,
Bluewater and Bowen) are characterised by moderate to high levels of development, with
groundwater extractions approaching or exceeding sustainable yields
(AWR 2005). Being of potable quality and easily accessible (i.e. shallow), extracted
groundwater is used extensively for irrigation, town and domestic water supplies. Despite high
levels of extraction, groundwater levels are reported to be stable in each of these highly
developed GMUs, although the Burdekin GMU will not sustain further development (DEWHA
2009). Groundwater development is considered to be low in the remaining GMUs.
The main soil types include relatively low-permeability (<0.3 m/day) duplex-type red-brown
earths and desert loams (Sodosol) in about 44 per cent of the area, high-permeability (1
m/day) prairie, chocolate, red and yellow podzolic soils (Dermosols) in about 24 per cent of
the area and high-permeability (1.3 m/day) red, yellow and grey earths and calcareous red
earths (Kandosol) in about 11 per cent (
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Table 9). Three main land uses include dryland agriculture (49 per cent of the area), irrigated
agriculture (19 per cent) and native vegetation (20 per cent) (Table 10).
Toowoomba Basalts
The Toowoomba Basalts aquifer is located in south-east Queensland and lies within two
climate types. About 86 per cent of its area lies within the equiseasonal hot (Cfa) and about
14 per cent within the equiseasonal–warm climate type (Cfb) (Table 8). It includes the
Toowoomba North, Toowoomba South, Toowoomba City, Warwick and Nobby Basalt GMUs.
The basalts form part of the Tertiary Main Range Volcanics, and groundwater is hosted in
fractures, vesicle and weathered zones of these basalts. Aquifers are intersected between 2
m and 155 m below surface, are typically 10 to 30 m thick and may be confined, semiconfined
or unconfined. Groundwater salinity ranges from fresh to brackish (DEWHA 2009).
Groundwater levels in the basalts are responsive to rainfall events and recharge occurs via
direct infiltration where units outcrop or through overlying well-drained soils. Sustainable
yields from the Basalt GMUs have been established empirically (from historical data) or from
recharge estimates derived from runoff and soil moisture models (DEWHA 2009).
Natural discharge from the Toowoomba Basalts occurs via outflow to the Condamine
Alluvium (to which it is hydraulically connected). Additionally, there is a high density of
irrigation, stock and domestic, and municipal supply bores across the area, with over 80 per
cent of groundwater extracted used for irrigation purposes (CSIRO/SKM 2010).
In this aquifer, low-permeability (0.03 to 0.09 m/day) black earths, grey, brown and red clay
soils (Vertosol) occur in about 65 per cent of the area and high permeability (0.8 to 1.8 m/day)
siliceous and earthy sands, alpine humus soils and some alluvial soils (Tenosol) occur in
about 22 per cent (Table 9). Dryland agriculture is the main land use in this area (82 per
cent). Native vegetation and irrigated agriculture use about 8 and 4 per cent of the aquifer
area, respectively (Table 10).
Gunnedah
The Gunnedah aquifer is located in northeast New South Wales and comprises a group of
GMUs associated with the sedimentary Gunnedah and Narrabri Formation aquifers, and
contemporaneous equivalents. The Gunnedah aquifer has an equiseasonal–hot climate type
(Cfa) in about 72 per cent of the area and an arid climate (BSh) in 28 per cent (Table 8).
The Narrabri and basal Gunnedah Formations are spatially associated with the current
surface water drainage systems and comprise primarily unconsolidated, interbedded sands,
gravels and clays (CSIRO/SKM 2010). The 15 to 50 m-thick Narrabri Formation comprises
recent alluvial fan sediments and is found either at the surface or up to 10 m below ground
level (CSIRO 2007). Groundwater in the Narrabri Formation is mostly fresh to brackish, but
can be saline, particularly away from surface water features (CSIRO/SKM 2010). The
underlying Gunnedah Formation ranges between 20 m and 45 m thick and groundwater is
typically fresher to brackish (CSIRO/SKM 2010). Underlying the Gunnedah Formation, but
spatially restricted to paleochannels—the deepest aquifers within parts of some of the GMUs
in the Gunnedah grouping—is the coarse-grained Cubbarroo Formation (CSIRO, 2007),
though these aquifers are included with the Gunnedah Formation for this study.
Groundwater is hosted in both the Narrabri and Gunnedah Formations, which are
hydraulically connected across most areas and act as one aquifer unit. The aquifers are
mostly unconfined and the watertable is typically intersected at 10 m below ground level. In
certain locations, the Gunnedah Formation is semi-confined to confined by clay layers (Barret
2009).
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Recharge to the Narrabri Formation occurs primarily through leakage from rivers and
watercourses and is supplemented by infiltration of floodwaters, diffuse rainfall recharge and
root-zone drainage associated with irrigation activities (CSIRO/SKM 2010). Recharge to the
Gunnedah Formation occurs primarily by downwards infiltration from the Narrabri Formation
(CSIRO 2007).
About 69 per cent of the aquifer area has black earthsand grey, brown and red clay soils
(Vertosol), and about 22 per cent has red-brown earths and desert loams (Sodosol) (
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Table 9). The hydraulic conductivity of the Vertosols ranges between 0.01 and 0.09 m/day,
whereas the hydraulic conductivity of the Sodosols varies between 0.1 and 0.5 m/day. Two
main land uses in the Gunnedah aquifer area include dryland agriculture in 86 per cent of the
area and irrigated agriculture in about 11 per cent (Table 10).
The groundwater resources of the Gunnedah grouping are among the most intensively
developed in New South Wales, with extracted water used for stock and domestic, irrigation
and town water-supply purposes (CSIRO 2007). The Gunnedah Formation aquifers form the
primary groundwater source and most of the high-yielding extraction bores are constructed
here. This has led to large drawdowns near regional centres (up to 20 m) and has induced
leakage from the overlying (and typically more saline) aquifer. In certain locations this has
resulted in dewatering of the Narrabri Formation (CSIRO/SKM 2010; CSIRO 2007; Barret
2009).
Pilbara
The Pilbara aquifer area lies within the arid climate type (mainly desert, Bwh, BSh) (Table 8).
The hydrogeology of the Pilbara region is described by Johnson and Wright (2001), Haig
(2009) and MWH (2009). The Pilbara grouping comprises three main aquifer groups: the
unconsolidated sedimentary aquifers associated with valleys (alluvium and colluviums);
chemically deposited aquifers (calcrete and pisolitic limonite); and fractured-rock aquifers.
The valleyfill deposits are up to 200 m thick, comprise various sedimentary sequences of clay,
sand and gravel, and form unconfined aquifers in connection with underlying basement rocks.
The chemically deposited aquifers form in palaeochannels with groundwater flow
predominately occurring through karstic features. Fractured-rock aquifers form in dolomitic
formations and within the fractured and mineralised ore bodies. Recharge mainly occurs via
streambed leakage during periods of high river flow. Direct rainfall recharge also occurs, but
to a lesser extent as rainfall in the area of this aquifer is the lowest of all the 14 priority
aquifers. The groundwater discharge occurs by outflow to river springs and pools,
evapotranspiration and evaporation from the soil surface in areas of shallow watertables. The
groundwater quality is mostly fresh to marginal (200 to 1000 mg/L TDS). Hypersaline
groundwater of up to 60 000 mg/L TDS also exists in the vicinity of Fortescue Marshes (AGC
Woodward Clyde 1994).
The main soils include siliceous and earthy sands and alluvial soils (Tenosols) in about 45 per
cent of the area, red-brown earths and desert loams (Sodosols) in about 26 per cent and red,
yellow, and grey earths, calcareous red earths (Kandosols) in 18 per cent (
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Table 9). The Tenosols are highly permeable (3.75 m/day). The Sodosols have low hydraulic
conductivity (0.1 m/day) and Kandosols have high conductivity (1.37 m/day). The main land
uses include dryland agriculture (68 per cent) and native vegetation (30 per cent). About 0.03
per cent of the area is used for mining (Table 10). The iron-ore industry is the major
groundwater user in the area, for mine dewatering, dust suppression, and mineral processing
(Johnson and Wright 2001).
Port Campbell Limestone
This aquifer is located within two climate types on the south-west coast of Victoria. About 58
per cent of the aquifer area occurs within the winter rainfall climate type (Csb) and 42 per cent
within the equiseasonal–warm climate (Cfb) (Table 8). The Port Campbell Limestone
grouping incorporates the Glenelg and Hawkesdale GMUs and the Nullawarre and Yangery
Groundwater Supply Protection Area. The mid-to late- Miocene Port Campbell Limestone is
the primary productive aquifer in this region and comprises primarily marine calcerenite. Clayrich marl increasingly interfingers the calcarenite with depth, such that only the top 50 to 200
m of the Port Campbell Limestone is considered a productive aquifer. The Port Campbell
Limestone is either found in outcrops or is overlain by hydraulically connected younger dune
sands and volcanics, and therefore it can be considered the watertable aquifer (DEWHA
2009). Groundwater is of good quality (≤1000 mg/L TDS approximately) and used extensively
for irrigation purposes.
The aquifer area has high to very high permeability (1.9 to 3 m/day) podzols, humus podzols
and peaty podzols (Podosols) in 36 per cent of the area, low to high permeability (0.25 to 1
m/day) red-brown earths and desert loams (Sodosols) in 24 per cent, medium to high
permeability (0.6 to 1.2 m/day) non-calcic brown soils and some red-brown earths
(Chromosols) in 19 per cent and medium to very high permeability (0.8 to 3 m/day) sandy and
alluvial soils (Tenosols) in about 11 per cent (
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Table 99). The aquifer area has dryland agriculture in 61 per cent of the area, native
vegetation in 13 per cent and pine plantations in 25 per cent. About 1 per cent has irrigated
agriculture (Table 10).
Coastal River Alluvium 4
The Coastal River Alluvium 4 grouping incorporates the alluvial (fluvial) aquifers on the
subtropical northern New South Wales and southern Queensland coasts. Of the area of the
aquifer, 29 per cent occurs within the tropics climate (Cwa) and 69 per cent in the
equiseasonal–hot climate (Cfa) (Table 8). The aquifers within this grouping comprise coarse
Quaternary floodplain sediments associated with the current drainage system. Hence, there is
a high degree of surface water–groundwater connectivity. Depths to watertable are typically 3
to 10 m below ground level and groundwater is mostly fresh to brackish (≤1000 mg/L TDS).
The GMUs within the Coastal River Alluvium 4 grouping are small to moderately sized (85 to
2
1942 km ).
Prairie soils, chocolate soils, some red and yellow podzolic soils (Dermosols) occur in 25 per
cent of the area with hydraulic conductivities from 1 to 1.5 m/day (
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Table 9). Red-brown earths and desert loams (Sodosols) occupy about 24 per cent of the
area. The hydraulic conductivity of these soils varies between 0.3 and 0.5 m/day. About 13
per cent of the area has podzolic soils, which are strongly acidic duplex type (Korosols) and
have medium conductivity (0.9 m/day). The main land uses in this aquifer include dryland
agriculture (64 per cent), irrigated agriculture (9 per cent), native vegetation (16 per cent) and
pine plantations (5 per cent). The GMUs are characterised by high levels of groundwater
development for irrigation, town supply and some industrial purposes. Over-extraction has led
to watertable declines and seawater intrusion in some areas (AWR 2005; NRMMC 2002).
Coastal Sands 4
The Coastal Sands 4 grouping incorporates the numerous Quaternary sand aquifers on the
subtropical east coast of Australia (approximately central Queensland to central New South
Wales). It has an equiseasonal–hot climate (Cfa) in about 98 per cent of the area; the
remaining 2 per cent has an equiseasonal–warm climate (Cfb) (Table 8). The GMUs within
2
this grouping, listed in Currie et al. (2010), are small to moderately sized, ranging from 22 km
2
to 1970 km and comprise primarily aeolian and marine sand-dune deposits
(AWR 2005). Aquifers can be up to 100 m thick and watertables are intersected three to 11 m
below ground level (AWR 2005). The aquifers are characterised by high infiltration rates and
the main recharge mechanism is diffuse rainfall recharge (AWR 2005). Recharge in the
Botany Sandbeds is estimated as 30 per cent of the rainfall (Timms et al. 2006).
Groundwater is generally of good quality (i.e. low salinity) in the sand aquifers, although in
most of the Coastal Sands 4 GMUs the level of development is broadly characterised as ‘low
level’ relative to sustainable yields. Localised areas of high-level development do exist where
groundwater is extracted for municipal, commercial, stock watering and crop irrigation
purposes (AWR 2005).
In many of these GMUs there is no potential for future development because of the possibility
of seawater intrusion. Additionally, many of the aquifers within this grouping, namely the
Tomago Sandbeds, Macleay Coastal Sands, Richmond Coastal Sands, Botany Sandbeds
and Bellinger Coastal Sands, have been classified as being at ‘high risk’ with respect to overextraction and land-use threats (i.e. contamination) (DLWC 1998). There are risks to
groundwater quality in the Stuart Point Sandbeds from higher arsenic concentrations, in the
Tweed River Coastal Sands from previous and current sand mining and the potential to
release naturally occurring heavy minerals, and in the Coffs Harbour Coastal Sands because
of the use of agricultural chemicals and fertilisers (NSW 2010).
The main soils include humic gleys, gleyed podzolic and some alluvial soils (Hydrosols) in
about 37 per cent of the area, humus podzolic and peaty podsols (Podosols) in 28 per cent,
and acidic duplexes (Korosols) in about 11 per cent (
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Table 9). About 9 per cent of the area has prairie soils, chocolatesoils and some red and
yellow podzolic soils (Dermosols). The hydraulic conductivity of these soils varies between
0.7 and 1.5 m/day.
Native vegetation is the main land use (46 per cent) followed by dryland agriculture (34 per
cent). Irrigated agriculture and plantations use about 2 and 4 per cent, respectively. About
0.04 per cent is devoted to mining (Table 10).
Otway Basin
The Otway Basin includes the Lower Limestone and Padthaway Coast Prescribed Wells
Areas in south-east South Australia. It lies within the winter rainfall climate type (Csb) (Table
8). The Otway Basin grouping contains two distinct, regionally extensive groundwater
systems: the Tertiary Confined Sands Aquifer (TCSA) and the overlying, unconfined Tertiary
Limestone Aquifer (TLA). The TLA forms the primary productive aquifer. Groundwater in the
TLA is typically fresh to brackish.
Recharge to the TLA (and the TCSA) occurs via inflow from the adjoining Dundas Plateau in
Victoria and the dominant flow direction is subsequently east to west (DWLBC 2006).
Recharge to the TLA in this area also occurs via diffuse rainfall infiltration and groundwater
levels are responsive to changes in the precipitation regime. In general, rainfall has declined
over time across the TLA and this has led to significant watertable declines in over half of the
management areas. This is due to both the direct and indirect mechanism of decreased
precipitation rates leading to an increased demand for groundwater resources (DWLBC
2006).
Compounding the effects of reduced precipitation are groundwater extractions that exceed
the sustainable yield of the TLA, resulting in widespread resource degradation, both in terms
of availability (declining groundwater levels) and water quality (increased salinity from salt
mobilisation) (DWLBC 2007). The sustainable yield of these areas is being recalculated
because previous estimates of the sustainable yield are less reliable.
About 51 per cent of the basin area has relatively high-permeability (1 m/day) duplex-type
red-brown earths and desert loams (Sodosols) (
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Table 9). Low-permeability (0.3 m/day) black earths, grey brown and red clays (Vertosols)
occur in about 18 per cent of the area and about 17 per cent has very high conductivity (3
m/day) earthy sands and alluvial soils (Tenosols).
About 80 per cent of the Otway Basin has dryland agriculture, plantations occupy about 10
per cent, and irrigated agriculture and native vegetation each cover about 4 per cent (Table
10). The groundwater is used extensively for town, stock and domestic supplies, by
commercial forestry and for the irrigation of crops and pasture (the latter, irrigation, is
responsible for up to 99 per cent of groundwater use) (AWR 2005). Commercial forestry
plantations are also considered to use groundwater through infiltration interception and direct
extraction where plantations overlie and access shallow groundwater. This type of water use
by pine plantations accounts for approximately 7 per cent of total available recharge (DWLBC
2007).
Adelaide Geosyncline 3
The Adelaide Geosyncline is a major geological feature of South Australia, extending from the
Fleurieu and Yorke peninsulas, through the Mount Lofty Ranges to the northen Flinders
Ranges. It has a winter rainfall climate (Csa, Csb) in about 57 per cent of the area and an arid
climate (BSk) in 35 per cent, as the rainfall in this area is particularly low (Table 8). Small
areas also lie within the equiseasonal hot and warm climate type. The region includes several
GMUs, which are listed in Currie et al. (2010).
The region is characterised by steep and undulating terrain with predominately fractured-rock
aquifers that form in Proterozoic metasediments. Sedimentary aquifers, such as the Permian
sands of the Fleurieu Peninsula, can also provide significant local supplies of groundwater.
The fractured-rock aquifers present throughout the Mount Lofty Ranges are recharged
predominantly via rainfall but may also receive some recharge from streams during periods of
high flow. Discharge from this aquifer occurs through springs and seeps at the break of slope
and as baseflow to streams. Discharge also occurs at depth (as groundwater through flow) to
the adjoining sedimentary aquifers of the Adelaide Plains, particularly in faulted zones.
Four main soil types are present in the area and include duplex-type, non-calcic brown soils
and red-brown earths (Chromosols) in about 59 per cent of the area, acidic duplex podzolic
soils (Korosols) in about 11 per cent, duplex type red-brown earths, grey-brown and red
calcareous soils (Calcarosols) in 11 per cent, and desert loams (Sodosols) in 10 per cent (
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107
Table 9). The hydraulic conductivity of the Chromosols varies between 0.4 m/day and
1.2 m/day. Kurosols have medium permeability (0.5 to 0.7 m/day). The hydraulic conductivity
of the Calcarosols and Sodosols varies between 0.1 m/day and 2 m/day. The main land-use
is dryland agriculture (85 per cent). Irrigated agriculture and plantations each use about 2 per
cent of the area, native vegetation about 3 per cent and mining about 0.01. per cent (Table
10).
Daly Basin
The Daly Basin aquifers refer to the thick (approaching 200 m) mid-Cambrian to early
Ordovician Tindall Limestone and Oooloo Dolostone aquifers (and equivalents) in the
Northern Territory. About 65 per cent of the basin occurs within the tropics climate (Aw) zone
and 35 per cent within the arid climate (BSh) with low rainfall (Table 8). Tindall Limestone is
the oldest formation. It is overlain by Jinduckin Formation, which in turn is overlain by Oolloo
Limestone (Begg et al. 2001). The aquifers are highly connected to the local surface water
systems, providing the primary water source for baseflows and, although there is the potential
to reliably supply large volumes of water for extractive purposes, modelling suggests that
current rates of extraction are close to or at the limits of recoverable groundwater extractions,
particularly in irrigation areas (CSIRO 2009d). The groundwater in the basal unit of the
Jinduckin Formation is unsuitable for domestic, stock or irrigation use due to dissolution of
gypsum in the water (Chin 1995). Recharge to the aquifers occurs via rainfall infiltration,
either diffusely or directly through sinkholes and dissolution hollows (Harrington et al. 2009).
The groundwater yield is lowest in areas underlain by the Jinduckin Formation (Jolly 1984).
The watertable varies throughout the year in the basin. Its depth ranges between 3 to 25 m
below ground level at sites underlain by Tindall Limestone, between 8 to 25 m at sites
underlain by the Jinduckin Formation and between 2 to 62 m at sites underlain by Oolloo
Limestone (Chin 1995). There is a large network of groundwater-dependent wetlands and
streams in the basin (Begg et al. 2001).
About 42 per cent of the basin has high hydraulic conductivity (1.3 to 1.4 m/day) red, yellow
and grey earths and calcareous red earths (Kandosols). Very high hydraulic conductivity (2 to
3.75 m/day) siliceous and earth sands and alluvial soils (Tenosols and Rudosols) occur in
about 46 per cent of the area (
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108
Table 9).
Dryland agriculture and native vegetation are the main land uses in this area, using about 66
per cent and 34 of the total area, respectively (Table 10). The land is also used for irrigated
agriculture (0.1 per cent) and mining (0.01 per cent). The water extraction is mainly for
agricultural and domestic uses. There were 290 groundwater licences during 2009–10 to
withdraw 126 GL of groundwate and. 70 surface water licences to withdraw about 171 GL
(NWC 2010).
Climate change impacts on rainfall and diffuse
recharge
This section describes the impacts of climate change on rainfall and diffuse recharge in the
high-priority aquifers. Table 11 lists the 80-year baseline historical period spatial variation in
minimum, maximum, range, mean and standard error of rainfall across each aquifer. The
same statistics for the median precipitation-scaling factors (PSF) under wet, median and dry
future climates are also listed in this table. Although the PSF were calculated in the same way
as the recharge scaling factor (RSF), an aquifer’s PSF does not correspond with its RSF, as
the wet, median and dry future recharge are not caused by the corresponding wet, median
and dry future rainfall. Also, RSFs were calculated through aggregation and reported as
median values in each aquifer area calculated from the medians of all cells in the area. Thus,
PSFs are suitable only for general comparisons with RSFs and any interpretation needs to
take these incompatibilities into account.
The RSFs are reported for four climate scenarios (historical, wet future, median future and dry
future) and three variabilities (wet 15 years, median 15 years and dry 15 years) (Table 12).
Further details of their calculation procedure are given in Chapter 4. For brevity, only the
RSFs for the median 15 years under each of the historical, wet, median and dry future climate
scenarios are discussed here.
When comparing the PSF with the RSF it is assumed that the 90th percentile of high global
o
warming (2.4 C) PSFs correspond to the median RSFs for the wet future climate, the 50th
o
percentile of medium global warming (1.7 C) PSFs corresponds to the median RSFs for the
o
median 15-years future climate, and the 10th percentile of high global warming (2.4 C) PSFs
corresponds to the median 15-years RSFs for the dry future climate. The projected changes
in rainfall and recharge under the wet, median and dry future climate are reported below for
each priority aquifer.
The small range under the median and dry future climates suggests smaller projected
changes in spatial variation of future rainfall. The PSF statistics for any future climate when
multiplied by the baseline rainfall statistics give estimates of the rainfall statistics of that future
climate.
To assess how rainfall and recharge trends vary across various aquifer areas, per cent
change from baseline 80-years historical-period rainfall and diffuse recharge was plotted for
each aquifer for the wet, median and dry future climates as shown in Figure 57 and Figure 58.
The rainfall is projected to decrease between 6 to 8 per cent under the wet future climate in
only three aquifer areas, namely, Newer Volcanics with an equiseasonal–warm climate type,
Port Campbell Limestone with a majority of the area in winter-rainfall climate type and Otway
Basin in the winter-rainfall climate type (see Table 8 for climate types in each high-priority
aquifer). In the Gunnedah and Daly Basin aquifer areas it is projected to increase by 14 to 16
per cent under the wet future climate. It is projected to remain unchanged in the Adelaide
NATIONAL WATER COMMISSION — WATERLINES
109
Geosyncline Aquifer area. For the remaining eight aquifer areas, the rainfall is projected to
increase by 8 to 11 per cent under the wet future climate.
Table 11: Statistics of 80-year baseline period rainfall and wet, median and dry future climates
for the priority aquifers
Aquifer
Minimum
Maximum
Range
Mean
Standard
error
80-year baseline rainfall (mm)
Lachlan
392
693
301
492
62
Newer Volcanics
528
913
385
703
79
Upper Condamine and Border Rivers Alluvium
552
780
228
627
27
Atherton Tablelands
956
1946
990
1488
246
Coastal River Alluvium 1
810
4221
3411
1566
977
Toowoomba Basalts
609
1233
624
735
132
Gunnedah
463
731
268
554
54
Pilbara
242
416
174
325
39
Port Campbell Limestone
600
871
271
735
52
Coastal River Alluvium 4
600
1989
1389
1245
296
1070
1861
791
1391
178
Otway Basin
487
820
333
632
78
Adelaide Geosyncline 3
277
964
687
519
143
Daly Basin
596
1642
1046
932
215
Coastal Sands 4
PSF for wet future climate
Lachlan
1.07
1.19
0.12
1.11
0.05
Newer Volcanics
0.92
0.94
0.02
0.93
0.00
Upper Condamine and Border Rivers Alluvium
1.06
1.12
0.06
1.11
0.01
Atherton Tablelands
1.10
1.10
0.00
1.10
0.00
Coastal River Alluvium 1
1.10
1.13
0.03
1.11
0.01
Toowoomba Basalts
1.06
1.11
0.04
1.09
0.02
Gunnedah
1.12
1.19
0.08
1.16
0.02
Pilbara
1.02
1.13
0.11
1.08
0.02
Port Campbell Limestone
0.92
0.94
0.02
0.92
0.00
Coastal River Alluvium 4
1.04
1.16
0.12
1.10
0.03
Coastal Sands 4
1.05
1.15
0.10
1.10
0.03
Otway Basin
0.92
1.00
0.08
0.94
0.03
Adelaide Geosyncline 3
0.96
1.14
0.18
1.01
0.07
Daly Basin
1.09
1.19
0.10
1.14
0.03
PSF for median future climate
Lachlan
0.96
0.99
0.03
0.98
0.01
Newer Volcanics
0.89
0.90
0.01
0.89
0.00
Upper Condamine and Border Rivers Alluvium
0.94
0.98
0.04
0.96
0.01
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110
Atherton Tablelands
0.98
0.98
0.00
0.98
0.00
Coastal River Alluvium 1
0.97
1.00
0.03
0.98
0.01
Toowoomba Basalts
0.94
0.96
0.02
0.95
0.01
Gunnedah
0.97
1.00
0.03
0.99
0.01
Pilbara
0.91
0.99
0.08
0.96
0.01
Port Campbell Limestone
0.88
0.90
0.02
0.88
0.00
Coastal River Alluvium 4
0.93
1.00
0.07
0.97
0.02
Coastal Sands 4
0.95
0.99
0.05
0.97
0.02
Otway Basin
0.88
0.90
0.02
0.89
0.01
Adelaide Geosyncline 3
0.89
0.95
0.06
0.91
0.02
Daly Basin
0.99
1.03
0.04
1.01
0.01
PSF for dry future climate
Lachlan
0.81
0.85
0.04
0.83
0.01
Newer Volcanics
0.77
0.78
0.02
0.77
0.01
Upper Condamine and Border Rivers Alluvium
0.77
0.81
0.04
0.78
0.01
Atherton Tablelands
0.86
0.86
0.00
0.86
0.00
Coastal River Alluvium 1
0.77
0.89
0.13
0.84
0.02
Toowoomba Basalts
0.78
0.80
0.02
0.78
0.01
Gunnedah
0.79
0.85
0.06
0.80
0.01
Pilbara
0.69
0.77
0.09
0.73
0.02
Port Campbell Limestone
0.76
0.78
0.03
0.77
0.01
Coastal River Alluvium 4
0.74
0.86
0.12
0.81
0.04
Coastal Sands 4
0.75
0.87
0.12
0.82
0.03
Otway Basin
0.75
0.78
0.03
0.76
0.01
Adelaide Geosyncline 3
0.74
0.77
0.03
0.75
0.01
Daly Basin
0.90
0.93
0.04
0.91
0.01
Table 12: Mean annual recharge rates under the baseline historical period and RSF under the
historical, wet, median and dry future climates
Aquifer
Lachlan
Baseline
80-year
mean
annual
recharge
(mm)
Recharge scaling factor (RSF) under
Historical
climate
Wet future
climate
Median
future
climate
Dry future
climate
58.9
1.05
1.47
1.08
0.82
121.8
1.05
1.17
0.93
0.69
28.6
1.06
1.52
1.02
0.62
Atherton Tablelands
540.9
0.99
1.15
0.94
0.72
Coastal River Alluvium 1
537.4
1.00
1.14
0.95
0.57
Newer Volcanics
Upper Condamine
and Border Rivers Alluvium
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111
Toowoomba Basalts
60.8
1.05
1.49
0.99
0.61
Gunnedah
24.5
1.06
1.71
1.13
0.76
Pilbara
13.6
1.00
1.21
0.83
0.45
Port Campbell Limestone
185.8
1.02
1.00
0.85
0.60
Coastal River Alluvium 4
362.5
1.00
1.23
0.98
0.73
Coastal Sands 4
302.8
1.02
1.44
1.03
0.72
Otway Basin
145.0
1.01
1.01
0.85
0.59
Adelaide Geosyncline 3
120.7
1.01
1.17
0.93
0.64
Daly Basin
147.7
0.95
1.51
1.03
0.86
60
Wet
Median
40
Dry
20
0
-20
-40
C
N
ew L
a
an er V ch
d
o la
C Ath B lca n
oa er R
n
st ton Al ics
al
lu
R T v
To ive abl ium
ow r A ela
oo llu nd
m viu s
ba m
B 1
Po
rt
G asa
un lts
C
C am
ne
oa p
da
st be
al
l l Pi l b h
R Li
iv m ara
e
e
C r Al sto
oa lu ne
st viu
Ad
al
m
el
ai O San 4
de tw d
G ay s 4
eo B
sy as
nc in
D line
al
y
3
Ba
si
n
-60
U
Percent change in rainfall
80
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112
Figure 57: Rainfall-scaling factors under the wet, median and dry future climates in the highpriority aquifers
Percent change in recharge
Wet
80
Median
60
Dry
40
20
0
-20
-40
U
C
N
ew L
a
an er V ch
d
o la
C Ath B lca n
oa er R
n
st ton Al ics
al
l
u
R T v
To ive abl ium
ow r A ela
oo llu nd
m viu s
ba m
B 1
Po
rt
G asa
un lts
C
C am
ne
oa p
da
st be
al
ll Pilb h
R Li
iv m ara
e
e
C r Al sto
oa lu ne
st viu
Ad
al
m
el
ai O San 4
de tw d
G ay s 4
eo B
sy as
nc in
D line
al
y
3
Ba
si
n
-60
Figure 58: Recharge-scaling factors under the wet, median and dry future climates in the
high-priority aquifers
The rainfall is projected to reduce in all aquifer areas except the Daly Basin under the median
future climate. In the Daly Basin a rainfall increase of 1 per cent is projected. The rainfall is
projected to reduce by 9 to 12 per cent in four aquifer areas, namely, Newer Volcanics, Port
Campbell Limestone, Otway Basin and Adelaide Geosyncline 3. In the remaining nine aquifer
areas it is projected to reduce by 1 to 5 per cent under the median future climate. This
suggests a similar per cent reduction in rainfall across the majority of the aquifer areas under
the median future climate.
The rainfall is projected to reduce in all aquifer areas under the dry future climate. In half of
the aquifers the projected reduction in rainfall varies from 22 to 27 per cent. Six aquifer areas
are projected to have rainfall reductions of 16 to 20 per cent. One aquifer (Daly Basin) is
projected to have 9 per cent reduction in rainfall under the dry future climate.
Therefore, whichever future climate eventuates it is likely to impact rainfall accordingly. In the
case of a wet future climate the rainfall is projected to increase modestly except in a few
aquifer areas. Under a median future climate the rainfall is less likely to change significantly
from the baseline period, and under a dry future climate the impacts on rainfall are likely to be
significant as all except one aquifer area have projected rainfall reductions of 16 to 27 per
cent.
The diffuse recharge is expected to remain unchanged in two aquifer areas (Port Campbell
Limestone and Otway Basin) under the wet future climate (Figure 58). It is projected to
increase between 14 and 23 per cent in six aquifer areas: Newer Volcanics, Atherton
Tablelands, Coastal River Alluvium 1, Pilbara, Coastal River Alluvium 4, and Adelaide
Geosyncline 3. Diffuse recharge is projected to increase most in the Gunnedah aquifer area
(71 per cent) under the wet future climate. In the remaining five aquifers it is projected to
increase by 44 to 52 per cent under the wet future climate. The increase in diffuse recharge is
NATIONAL WATER COMMISSION — WATERLINES
113
in response to a projected increase in rainfall in 10 of the 14 aquifers under the wet future
climate.
The recharge is projected to increase by 8 to 13 per cent in the Lachlan and Gunnedah
aquifer areas under the median future climate, although rainfall is projected to remain
unchanged in these areas. It is projected to slightly increase (up to 3 per cent) in the Upper
Condamine and Border Rivers Alluvium, Coastal Sands 4 and the Daly Basin and slightly
decrease (up to 2 per cent) in the Toowoomba Basalts and Coastal Rivers Alluvium 4 aquifer
areas under the median future climate. In four aquifer areas (Atherton Tablelands, Coastal
River Alluvium 1, Adelaide Geosyncline and Newer Volcanics) the diffuse recharge is
predicted to decrease by 5 to 7 in response to a projected reduction in rainfall of between 2
and 11 per cent. Substantial recharge decreases of 15 to 17 per cent are expected in the
Pilbara, Port Campbell Limestone and Otway Basin aquifer areas under the median future
climate, where the rainfall is projected to decrease by 4 to 12 per cent.
Recharge is projected to reduce in all aquifer areas under the dry future climate. It is expected
to reduce by 14 to 18 per cent in the Lachlan and Daly Basin aquifer areas in response to
reductions in projected rainfall of between 9 and 17 per cent (compare Figure 58 and Figure
57). Large recharge reductions of 40 to
55 per cent are expected in the Coastal Rivers Alluvium 1, Toowoomba Basalts, Pilbara and
Otway Basin aquifer areas in response to projected reductions in rainfall of between 16 and
24. In the remaining eight aquifer areas recharge reductions of 23 to 39 per cent are expected
under the dry future climate in response to rainfall reductions of 14 to 25 per cent.
In summary, in most aquifer areas the diffuse recharge is likely to increase under the wet
future climate. Under the median future climate it is projected to either remain unchanged or
increase in seven of the
14 aquifer areas and decrease in the remaining seven. Under the dry future climate, large
reductions in diffuse recharge are likely in eight aquifer areas and very large reductions are
expected in four aquifer areas.
The baseline 80-year historical period mean annual diffuse recharge for each high-priority
aquifer is listed in Table 12. The largest climate change impacts on diffuse recharge are likely
in the Pilbara Aquifer area where the historical mean annual diffuse recharge is lowest due to
its location within the arid climate. Relatively large impacts on diffuse recharge are expected
in the Gunnedah and Upper Condamine Border River Alluvium aquifer areas, both of which
are mainly located in the equiseasonal–hot climate type and have low historical mean annual
diffuse recharge. The Lachlan Aquifer area, almost half of which is located in the arid climate
type, also receives lower diffuse recharge. This aquifer area is likely to be impacted by
climate change only if a dry climate occurs in the future. The historical mean annual diffuse
recharge is relatively large in the Coastal River Alluvium 4 and Coastal Sands 4, and very
large in the Atherton Tablelands and Coastal River Alluvium 1. Climate change impacts on
diffuse recharge in these aquifers are likely to be modest under the median future climate and
substantial to large under a dry future climate.
Climate change impacts on agriculture, water
supply and environment
Current groundwater use within the priority aquifers areas is summarised in Table 13 and
descibed below for individual aquifers.
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114
Lachlan
The main uses of groundwater include irrigation (80) and domestic and town water supplies
(20 per cent). Groundwater is very important to support agriculture and domestic supplies in
this aquifer. Total groundwater use is about 59 per cent of its sustainable yield (111 GL/year).
It is an overallocated system with total allocation of 165 GL/year. The surface water use is 53
per cent of its sustainable yield. About 41 per cent of the total water extracted is from
groundwater. The groundwater resource is expected to increase as a result of projected
increase in diffuse recharge under the wet and median future climates. Therefore no impacts
on agriculture, water supply and environment are expected if either the wet or median climate
eventuates in the future. However, an impact is expected under the dry future climate since it
is already an overallocated system.
The groundwater resource is also expected to reduce due to a reduction in the localised
recharge, since rainfall is projected to reduce impacts on surface runoff, flow volumes and
duration. However, localised recharge can also increase because of lower watertables that
increase the hydraulic gradient from the river to groundwater (in connected streams), making
more storage space available for infiltration of water. Without proper analysis and
quantification of the fluxes into and out of groundwater systems it is not possible to make any
valid conclusions about the impact of climate change on localised recharge. Given the
resource utilisation level in this overallocated system, the likely resource reduction under the
dry future climate warrants a high level of management response that includes detailed
knowledge of aquifers, monitoring throughout the area, understanding of water balance,
determination of GDEs, and regional groundwater models to predict the impacts of climate
change and abstractions on the resource. This level of management response is necessary to
help allocate the resource to various use categories based on detailed analysis and thorough
assessment of the system.
.
NATIONAL WATER COMMISSION — WATERLINES
115
20
20
Agriculture
132
52.3
80
80
Total
165
65.3
100
100
Domestic and town water supplies
5.4
23.5
Commercial and industrial
0.6
2.6
16.9
73.9
0
0
22.9
100
Total
Domestic and town water supplies
Commercial and industrial
Agriculture
Mining
Total
Domestic and town water supplies
Agriculture
6.4
5.2
3.8
3.8
3
2.4
1.8
1.8
159.4
127.7
94.4
94.4
0
0
0
0
168.8
135.3
100
100
1.7
1.4
7.5
7.5
21.6
17.3
92.5
92.5
Dry future
climate
Median
future
climate
Expected recharge
change (%) under
Wet future
climate
Surface water extraction as %
of surface water sustainable
yield
GW extraction as % of total
extraction
Surface water use (GL/yr)
GW use as per cent of
sustainable yield
GW sustainable yield
(GL/yr)
(%)
13.1
Mining
Atherton Tablelands
Per cent of
33
Agriculture
UC and Border River
Alluvium
total use
(GL/yr)
Newer Volcanics
Per cent of total
Domestic and town water supplies
entitlement
(%)
Lachlan
Estimated use
Use category
Entitlement
Aquifer
(GL/yr)
Table 13: Groundwater use categories, allocation and utilisation levels and expected changes in diffuse recharge under future climates in high-priority
aquifers
111
59
92
53
41
47
8
–18
43
53
18
72
55
17
–7
–31
97
140
60
141
69
52
2
–38
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Total
Coastal River Alluvium
1
Toowoomba Basalts
23.3
18.6
100
100
Domestic and town water supplies
2.9
2.4
3.2
3.2
Commercial and industrial
9.4
7.5
10.2
10.2
Agriculture
79.7
63.8
86.6
86.6
Total
92.1
73.7
100
100
Domestic and town water supplies
5.1
4.1
11.1
11.1
Commercial and industrial
1.1
0.9
2.4
2.4
39.8
31.8
86.5
86.4
46
36.8
100
100
Agriculture
Total
Gunnedah
Pilbara
Domestic and town water supplies
44.4
11.5
Agriculture
342.9
88.5
Total
387.3
100
18
102
13
100
59
15
–6
–28
139
53
3
100
96
14
–5
-43
61
60
8
100
82
49
–1
-39
357
109
157
35
71
71
13
-24
335
71
20
11
92
21
–17
-55
88
47
28
41
60
0
–15
-40
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Domestic and town water supplies
Commercial and industrial
Agriculture
Mining
Port Campbell
Limestone
Total
237
Domestic and town water supplies
8.7
21
Commercial and industrial
0.8
2
31.6
76.7
Mining
0.1
0.2
Total
41.2
100
Domestic and town water supplies
35.1
9.8
6.6
1.8
Agriculture
Coastal River Alluvium
4
Commercial and industrial
Coastal Sands 4
Otway Basin
Agriculture
315.4
88.3
Total
357.1
100
14.2
23.8
Commercial and industrial
0.3
0.5
Agriculture
2.7
4.6
Mining
10
16.8
Unknown
32.3
54.4
Total
59.5
100
2
0.7
0.1
0
290.4
99.3
0
0
292.5
100
Domestic and town water supplies
Domestic and town water supplies
Commercial and industrial
Agriculture
Mining
Total
Adelaide Geosyncline 3
424
84
47
49
88
23
–2
-27
410
15
0
0
100
44
3
-28
1326
22
5
10
98
1
–15
–41
117
23
61
66
30
17
–7
–36
329
19
24
1
73
51
3
–14
Domestic and town water supplies
Commercial and industrial
Agriculture
Mining
Total
Daly Basin
26.7
Domestic and town water supplies
7.6
21.1
28.6
33.2
Commercial and industrial
0.1
1.3
0.4
2
Agriculture
18.9
41.3
71
64.8
Total
26.5
63.7
100
100
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118
Newer Volcanics
The Newer Volcanics is a relatively small groundwater resource system with a sustainable
yield of 43 GL/year. The total groundwater use (23 GL/year) is about 53 per cent of the
sustainable yield. Out of total groundwater extracted, 74 per cent is used for agriculture, 24
per cent for domestic and town water supplies and 3 per cent for commercial and mining
purposes. The surface water use (18 GL/year) from surface water systems is at 72 per cent of
the surface water sustainable yield. Out of total water extraction, about
56 per cent is extracted from groundwater. The groundwater-use data indicates that
agriculture, domestic and town water supplies and mining are groundwater-dependent and
could be impacted if climate change causes reductions in groundwater recharge.
Diffuse rainfall recharge is the dominant recharge mechanism in this aquifer area. Because of
shallow watertables in many parts of this aquifer, groundwater discharge occurs to surface
water systems. The groundwater recharge is expected to increase (by 17 per cent) under the
wet future climate, which is likely to increase the groundwater resource. However,
groundwater recharge is likely to decrease under the median and dry future climates and may
impact on water supplies, agriculture, industry and the environment. Because of reductions in
diffuse recharge, groundwater levels are expected to decline, which in turn is likely to impact
groundwater discharge to surface water systems. Impacts on GDEs and the environment are
likely because of a reduction in groundwater discharge to surface water systems. This may
also lead to a reduction in localised recharge from the lower reaches.
Managing such impacts requires detailed knowledge of aquifers in areas of major abstraction,
supported by monitoring and modelling close to major abstraction centres. An appropriate
management response can help mitigate these impacts as the resource use is at 53 per cent
of the sustainable yield. Detailed assessment of the sustainable yield under the median and
dry future climates, allocation of the resource and quantification of the fluxes from
groundwater to surface water systems through groundwater modelling can help manage the
impacts of climate change on agriculture, water supplies, industries and the environment.
Upper Condamine and Border Rivers Alluvium
The Upper Condamine and Border Rivers Alluvium is a substantial groundwater resource
system with a sustainable yield of 97 GL/year. The groundwater allocation, at 140 per cent of
the sustainable yield, indicates its importance and significance as a resource. The
groundwater utilisation level is 97 per cent, which is almost approaching its sustainable yield.
Agriculture is the largest groundwater user (94 per cent), followed by domestic and town
water supplies (4 per cent). The remaining 2 per cent of the total groundwater use is for
commercial and mining industry purposes. The surface water use is also at 141 per cent of its
sustainable yield, which again indicates the importance of and pressure on water resources
for agriculture, water supplies and other industries. Since both surface water and groundwater
systems are already overallocated, any recharge reductions due to climate change will
require a careful management response.
Groundwater recharge mainly occurs via localised recharge, although diffuse recharge also
occurs from seasonal rainfall. Groundwater discharge also occurs to surface water systems
because of the connectivity of surface and groundwater systems,. The groundwater resource
is likely to increase due to a projected increase in diffuse recharge under a wet future climate
by more than 50 per cent relative to the baseline 80-year historical period. The groundwater
resource may also increase due to an expected increase in localised recharge as rainfall is
projected to increase under the wet future climate. The groundwater discharge to surface
water systems is expected to increase under the wet future climate. A median future climate
is projected to slightly increase the groundwater recharge rates (2 per cent), and therefore no
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119
impacts on agriculture, domestic and town water supplies, industry and environment are
likely, provided the resource use is sustainable under current conditions and groundwater
abstraction regimes remain unchanged. The localised recharge is likely to remain unchanged
or slightly decrease under the median future climate. No major changes in the groundwater
discharge to surface water systems are expected under the median future climate.
Large reductions (38 per cent) in diffuse recharge are expected under the dry future climate.
Localised recharge may also reduce significantly because of substantial reductions in rainfall
and its impacts on surface runoff, flow volumes and flow duration. Projected reductions in
both diffuse and localised recharge mean the watertables are likely to decline and thus impact
on groundwater discharge to surface water systems. If this climate eventuates, large impacts
on agriculture, water supplies, industry and environment are likely. Managing such impacts,
given the resource utilisation is approaching its sustainable yield and the system is already
overallocated, requires the highest level of management response, including a detailed
understanding of hydrogeology, calibrated groundwater models that can predict the effects of
climate change in abstraction regimes, and intensive water-level monitoring, especially in
environmentally sensitive areas. A detailed and very thorough assessment of the groundwater
system, including all of the above mentioned components, together with adjustment of the
sustainable yield and allocation, may help manage the impacts of the dry future climate. The
highest level of management response is required, even if resource utilisation is considered in
isolation.
Atherton Tablelands
The Atherton Tablelands aquifer has a relatively small groundwater resource with a
sustainable yield of 18 GL/year. It is an overallocated (23 GL/year) system. Groundwater use
is also above its sustainable yield (102 per cent). Both allocation and utilisation levels
highlight the groundwater stress level and its high importance as a resource. Agriculture uses
about 93 per cent of the total groundwater and domestic and town water supplies use about 7
per cent. Surface water use is also at 100 per cent of the surface water sustainable yield.
About 59 of total water extraction comes from groundwater, highlighting the high dependence
on groundwater supplies.
Groundwater recharge mainly occurs via diffuse recharge. Groundwater discharge also
occurs to surface water systems because of shallow watertables in many areas. Climate
change is likely to have a wide range of impacts on groundwater recharge, ranging from a 15
per cent increase under the wet future climate to a 28 per cent reduction under the dry future
climate relative to the historical 80-year baseline period. Diffuse recharge is also expected to
reduce moderately (by 6 per cent) under the median future climate. Expected recharge
reductions under median and dry future climates are likely to cause significant groundwater
resource reductions and impacts on both agriculture and domestic and town water supplies,
which already use groundwater above its sustainable yield. Overallocation, overutilisation and
likely recharge reductions under the median and dry future climates require the highest level
of management response. This should include a detailed understanding of hydrogeology,
calibrated groundwater models to predict the impacts of climate change and abstraction
regimes on the groundwater resource and its sustainable allocation and use, intensive
groundwater monitoring and monitoring of environmentally sensitive areas. Because the
groundwater system is highly connected to the surface water drainage system, discharge
from the groundwater system to the surface water system is also expected to reduce under
the median and dry future climates as a result of lower watertables. This will impact GDEs
and groundwater abstractions, if any, from streams. This necessitates intensive monitoring of
streams and an evaluation of the impacts on GDEs and their management.
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Coastal River Alluvium 1
The Coastal River Alluvium aquifer is a significant groundwater resource system. Its
sustainable yield is 139 GL/year. Total allocations amount to about 92 GL/year. Total
groundwater use is 74 GL/year, which is about 53 per cent of the sustainable yield. Main
groundwater uses include agriculture (86 per cent of the total use), commercial and industrial
(10 per cent) and domestic and town water supplies (3 per cent).The surface water use (3
GL/year) is 100 per cent of the surface water sustainable yield.
Localised recharge is the dominant recharge process. Diffuse recharge also occurs. Because
of shallow watertables, a high degree of surface and groundwater connectivity and
groundwater discharge occurs to surface water systems. The sensitivity of diffuse and
localised recharge to climate change could be high due to large mean annual rainfall and
shallow groundwater systems. The projected diffuse recharge estimates show a wide range of
recharge variability under various future climates. The projected diffuse recharge ranges from
a substantial increase (14 per cent) under the wet future climate to a moderate reduction (5
per cent) under the median future climate and a large (43 per cent) reduction under the dry
future climate relative to the historical 80-year baseline period. Moderate to large expected
reductions in diffuse recharge under the median and dry future climates are likely to lower the
shallow watertables, which may affect surface and groundwater connectivity and fluxes.
Change in fluxes to and from groundwater systems is also likely from climate change impacts
on surface water such as reduced runoff, frequency and river flow periods. Expected
reductions in diffuse and localised recharge are likely to impact agriculture, commercial and
mining industries, domestic and town water supplies and the environment, especially when
the surface water use is already at 100 per cent of the sustainable yield. An increase in
localised recharge is also likely because the decline in shallow watertables makes it possible
to accommodate more localised recharge as a result of increased storage availability. Proper
quantification of the fluxes to and from groundwater due to changes in rainfall, surface runoff,
flow duration and flow volumes is required to make any valid conclusions about the impact of
climate change on localised recharge and discharge to surface water systems. Management
interventions, including a detailed knowledge of aquifers in major borefields, supported by
monitoring and modelling, and groundwater monitoring can help optimise the allocation of the
groundwater resource to various use categories and to manage the climate change impacts.
Toowoomba Basalts
The Toowoomba Basalts is a relatively small groundwater resource with a sustainable yield of
61 GL/year. The groundwater allocation and use are 46 and 37 GL/year, respectively. The
surface water use is 100 per cent of the surface water sustainable yield. Groundwater is
important for agriculture, commercial and industrial supplies and domestic and town water
supplies. About 86 per cent of the groundwater use is for agriculture. Industry and town water
supplies consume about 2 and 11 per cent of the total groundwater use, respectively.
Groundwater supply is critical for all three main use categories. Groundwater recharge mainly
occurs via diffuse rainfall recharge and is relatively low.
There is a large variability in projected diffuse recharge ranging from a 49 per cent increase
under the wet future climate to a 39 reduction under the dry future climate relative to the
baseline 80-year historical period. No recharge changes are expected under the median
future climate. The recharge changes are proportionately large relative to a low absolute
recharge rate. The groundwater resource is likely to increase under the wet future climate and
remain unchanged under the median future climate. However, large groundwater resource
reductions are expected under the dry future climate, which will have large impacts on
groundwater-dependent industries and uses, including agriculture, industry and domestic
water supplies. Managing such impacts requires an appropriate level of response to ensure
NATIONAL WATER COMMISSION — WATERLINES
121
quantification of the groundwater fluxes under climate change through modelling, prediction of
the impacts of various abstraction regimes on the resource, and allocation of the resource to
various uses to ensure sustainability.
Gunnedah
The Gunnedah aquifer is a very large groundwater resource with a sustainable yield of
357 GL/year. The groundwater use (387 GL/year) is above its sustainable yield. The surface
water use, however, is only 35 per cent of the surface water sustainable yield. Of the total
water extracted, about 71 per cent is from groundwater, which indicates its importance as a
resource. The main groundwater-use categories include agriculture (using about 89 per cent
of the total groundwater extraction) and domestic and town water supplies (11 per cent).
Localised recharge is the dominant recharge mechanism because of high surface and
groundwater connectivity. A small amount of diffuse recharge also occurs. Groundwater
recharge is likely to be impacted if climate change impacts surface runoff.
Relatively large increases in diffuse recharge are projected under the wet future climate. A
substantial increase (13 per cent relative to the baseline 80-year historical period) in recharge
is also expected under the median future climate. A dry future climate is likely to cause a
substantial reduction (24 per cent) in diffuse recharge relative to the baseline period. These
expected changes are projected to be very small in terms of absolute diffuse recharge. The
changes are expected to occur in the localised recharge under both the wet and dry future
climate. The wet future climate may increase and dry future climate may decrease the
localised recharge due to changes in surface runoff as a result of projected changes in
rainfall. The localised recharge can also increase under the dry future climate because of the
extra storage space available to accommodate more localised recharge as a result of lower
watertables. Without proper assessment of the surface water and groundwater connectivity
and quantification of the fluxes to and from groundwater that change due to climate change, it
is not possible to make any valid judgments about the impact of climate change on localised
recharge. Given the resource use is above the sustainable yield and likely substantial impacts
of climate change on diffuse and localised recharge, the highest level of management
response is warranted for this aquifer area. The management response should include a
detailed understanding of hydrogeology, calibrated groundwater models, quantification of
surface water–groundwater interactions and monitoring of surface and groundwater systems,
and prediction of the impacts of climate change and abstraction regimes on fluxes between
surface water and groundwater to ensure allocation of the groundwater resource on a
sustainable basis.
Pilbara
The Pilbara aquifer is a large groundwater resource with a sustainable yield of 335 GL/year.
The groundwater use is 237 GL/year, which is about 71 per cent of the groundwater
sustainable yield. A small volume (20 GL/year) of surface water is also extracted, which is
only 11 of the surface water sustainable yield. The major groundwater users include the
mining industry and domestic and town water supplies. A small volume of water is also
extracted for pastoral requirements. The largest groundwater user is the mining industry,
which abstracts groundwater for mine dewatering, dust suppression, mineral processing and
ore beneficiation. The groundwater abstracted for dewatering is often used in mineral
processing or released at controlled points into surface water drainage systems. Groundwater
recharge occurs both via diffuse and localised recharge, with localised recharge being the
dominant recharge process.
Historically, a very small proportion of mean annual rainfall occurs as diffuse recharge, which
is projected to change due to climate change. The diffuse recharge is projected to increase
NATIONAL WATER COMMISSION — WATERLINES
122
substantially (21 per cent) under the wet future climate relative to the baseline 80-year
historical period. Substantial to very large reductions in diffuse recharge are expected under
the median and dry future climates, respectively. The low rainfall projected under these
scenarios will affect surface water flows, volumes and duration in the surface water systems
that may in turn impact the localised recharge as there is high surface water–groundwater
connectivity in this aquifer area.
The localised recharge to alluvial systems, such as Millstream, is already sporadic. This may
become even more variable in the future because of variations in the intensity and frequency
of cyclones in the area. It is predicted that there may be fewer cyclones in future, despite sea
temperatures rising, but those that do form may be more intense, bringing more rainfall. As
most alluvial systems ‘fill and spill’, the time between events becomes crucial. The PSF and
RSF do not take this into account, which is a deficiency in the method used to estimate these
scaling factors.
Lower watertables expected under the median and dry future climates due to lower diffuse
recharge may not only impact the groundwater resource but also the surface water–
groundwater connectivity and fluxes to and from groundwater systems and groundwaterdependent ecosystems. Lower watertables mean less groundwater abstraction for use in
dewatering for mining. The impacts on the mining industry, being the main groundwater user
in the area, can be substantial if the amount currently used for dewatering becomes less than
required for processing and dust suppression due to climate change. This requires a detailed
assessment of the impact of climate change on fluxes to and from groundwater systems and
its impacts on the groundwater resource. High water-utilisation levels, projected reductions in
diffuse recharge and likely changes in localised recharge under the median and dry future
climates, and the dependence of mining industry on the groundwater resource, all require the
highest level of management response to ensure the use and management of the resource is
sustainable. Detailed assessments of the groundwater resource through well-calibrated
groundwater models, including the prediction of climate change impacts and groundwater
abstractions on groundwater, will help ensure its allocation at sustainable levels. The
importance of localised recharge in this area makes it also imperative to quantify these
interactions and fluxes to and from groundwater under projected future climates, along with
intensive monitoring of environmentally sensitive areas. Knowledge of the impact of projected
future changes in cyclone frequency and intensity and the consequent effects on localised
recharge is also required.
Port Campbell Limestone
The Port Campbell Limestone is a significant groundwater resource with a sustainable yield of
88 GL/year. The uses of groundwater and surface water are 47 and 41 per cent of
sustainable yields, respectively. Of total groundwater use, about 77 per cent is used by
agriculture and 21 by domestic and town water supplies. Groundwater use by the commercial
and mining sectors is very small. About 60 per cent of total water extraction is from
groundwater, indicating the high importance of the resource. Diffuse recharge is the main
recharge process and significant recharge occurs annually through this process.
The diffuse groundwater recharge is projected to remain unchanged under the wet future
climate and, therefore, no impacts are likely on agriculture and town water supplies.
Substantial to large recharge reductions, however, are expected under the median and dry
future climates, respectively, which can impact agriculture and town water supplies. Since
groundwater use is modest, the impacts of the median and dry future climates can be
managed through an appropriate level of management response involving detailed knowledge
of the aquifers in major borefields, supported by monitoring and modelling, prediction of the
impacts of future climates and abstraction regimes on groundwater resource, and allocation of
the resource accordingly.
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123
Coastal River Alluvium 4
The Coastal River Alluvium 4 is a large groundwater resource with a sustainable yield of
424 GL/year. The groundwater use of 357 GL/year is 84 per cent of the groundwater
sustainable yield; whereas surface water use is about 49 per cent of the surface water
sustainable yield. Of total water extraction, 88 per cent is from groundwater, highlighting its
importance as a resource. Of total groundwater use, 88 per cent is utilised by agriculture, 10
per cent by domestic and town water supplies and less than 2 per cent for commercial and
industrial purposes.. Replenishment of the groundwater resource is mainly through localised
recharge. Diffuse recharge also occurs and is also a significant source of groundwater
replenishment. Watertables are shallow in many areas and surface and groundwater systems
are highly connected.
The projected groundwater recharge variability due to climate change is large, ranging from a
diffuse recharge increase (23 per cent) under the wet future climate to a reduction (27 per
cent) under the dry future climate, relative to the baseline 80-year historical period. Only a
slight reduction in diffuse recharge is expected under the median future climate. The changes
in surface runoff volumes and flow duration due to the dry future climate are likely to impact
the watertables and surface and groundwater connectivity, and change localised recharge to
groundwater systems. Changes in localised recharge need quantifying as this is the main
recharge mechanism in this aquifer area. Besides reduced diffuse recharge, if the localised
recharge also reduces under the dry future climate, impacts on agriculture, domestic and
town water supplies and environment are likely. As these are coastal aquifers, the watertables
are not expected to fall that much because of sea level acting as the base. High utilisation
levels of these highly significant, important and stressed resources need a higher level of
management response to effectively manage the impacts of the dry future climate. Such a
management response may include a detailed knowledge of aquifers, groundwater monitoring
throughout the area, and measurement and modelling to quantify interactions between
surface and groundwater systems and to predict the impacts of climate change on localised
groundwater recharge. It may also include the development of regional groundwater models
to predict the impacts of abstraction regimes and climate change on groundwater fluxes and
resources and allocation to various uses, and determination and monitoring of important
groundwater-dependent ecosystems.
Coastal Sands 4
This is a large groundwater resource with a sustainable yield of 410 GL/year. The total
groundwater use is only 15 per cent of the sustainable yield. The surface water use is less
than 1 per cent of the surface water sustainable yield of 18 GL/year. Therefore, almost 100
per cent of total water extraction is from groundwater. Groundwater is mainly used for
agriculture (59 per cent of total groundwater use), domestic and town water supplies (24 per
cent) and mining (17 per cent). Groundwater is mainly replenished through diffuse recharge
from rainfall; recharge is high due relatively high mean annual rainfall. There are no significant
surface water–groundwater interactions in the area, although the watertables are shallow in
many areas. For this reason localised recharge is not significant.
Variation in projected diffuse recharge is large under the three future climates. A large
increase in diffuse recharge is expected under the wet future climate and a large reduction is
expected under the dry future climate relative to the baseline 80-year historical period. A
slight reduction in recharge is also expected under the median future climate. Although large
reductions in recharge are expected under the dry future climate, their impact on agriculture,
water supplies and the mining industry may not be significant due to the low water-utilisation
level. A management response to quantify the impacts of climate change and abstraction on
allocation and sustainable yield will help better manage the resource under changing climate.
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It should be noted that current estimates of sustainable yield may not reflect sustainability for
coastal aquifers due to potential sea water intrusion. Thus, the utilisation levels may not be
that low when compared with reliable sustainable yield estimates.
Otway Basin
The Otway Basin is a very large groundwater resource with a sustainable yield of
1326 GL/year. Groundwater use is about 22 per cent of the sustainable yield and surface
water use is low at 10 per cent of the surface water sustainable yield. About 98 per cent of
total water extraction is from groundwater, which is very important for the agriculture industry.
Over 99 per cent of total groundwater use is by agriculture, with less than 1 per cent used by
domestic and town water supplies. Groundwater gets its replenishment from diffuse rainfall
recharge, which is a significant proportion (23 per cent) of mean annual historical rainfall.
Many areas have shallow watertables but there are not significant surface water–groundwater
interactions and, therefore, localised recharge is not an important mechanism in this aquifer
area.
The projected changes in diffuse recharge are minimal under the wet future climate. However,
substantial to large reductions in diffuse recharge are expected under the median and dry
future climates relative to the baseline 80-year historical period. The impacts on agriculture
are expected to be minimal even if a dry climate eventuates in the future, mainly because of
the low water-utilisation level (provided it remains at current levels). A detailed assessment of
the groundwater resource under the median and dry future climates and review of allocation
limits and sustainable yield are required for effective management of the groundwater
resource under changing climatic conditions.
Adelaide Geosyncline 3
The Adelaide Geosyncline 3 is a significant groundwater resource with a sustainable yield of
117 GL/year, with about 23 per cent of this currently utilised. Surface water use is 61 GL/year,
which is about 66 of the surface water sustainable yield. About 30 per cent of total water
extraction is from groundwater. Groundwater-use data was not available for this aquifer but
should be similar to other aquifer areas, and includes irrigation, domestic and town water
supplies and industry industry. Groundwater replenishment is mainly through diffuse recharge
from rainfall, which is about 23 of the baseline 80-year mean annual rainfall.
There is large variability in diffuse recharge under future climates, ranging from an expected
increase of 17 per cent under the wet future climate to a decrease of 36 per cent under the
dry future climate, relative to the baseline historical period. Diffuse recharge is also expected
to reduce by about 7 per cent under the median future climate. Because of expected
reductions in diffuse recharge, the groundwater resource is likely to reduce under the median
and dry future climate. Since the groundwater utilisation level is relatively low, the impacts on
agriculture, domestic and town water supplies, commercial and mining industries and the
environment are likely to be less significant at current allocation levels. Impacts are likely if
allocation increases in the future due to increased demand for groundwater. An appropriate
management response can help better manage the impacts of climate change on agriculture,
water supplies, industry and the environment.
Daly Basin
The Daly Basin is a large groundwater resource with a sustainable yield of 329 GL/year, with
groundwater use at only 19 per cent of the groundwater sustainable yield. Surface water use
as a percentage of surface water sustainable yield is also very low (1 per cent). About 73 per
cent of total water extraction is from groundwater, highlighting its importance for supporting
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various water-consuming industries. The two main groundwater users are agriculture (65 per
cent of total groundwater extractions) and domestic and town water supplies (35 per cent).
The watertables are shallow in many areas and there are significant surface water–
groundwater interactions in the area. Both diffuse and localised recharge are important
mechanisms that replenish the groundwater resource. The diffuse recharge replenishment
has been a small proportion (16 per cent) of mean annual historical rainfall.
The projected changes in diffuse recharge due to future climate change are large. They range
from a 51 per cent increase in diffuse recharge under the wet future climate to a 14 per cent
reduction under the dry future climate, relative to the baseline 80-year historical period.
Diffuse recharge is also expected to increase slightly under the median future climate.
Because of the increase in recharge expected under the wet and median future climates, the
groundwater resource is expected to increase. Therefore, no impacts on agriculture, water
supplies and the environment are likely if either the median or wet climate eventuates.
Localised recharge is also likely to increase under these future climates. However, it is
projected to decrease under the dry future climate due to changes in surface runoff volumes
and duration.
Reductions in diffuse and localised recharge, where predicted under the dry future climate,
are less likely to significantly impact agriculture and town water supplies because of low
groundwater-utilisation levels. It may, however, impact the environment because of reduced
groundwater discharge to surface water bodies resulting from lower watertables. A
management response that evaluates the groundwater resource, its allocation and
sustainable yield under projected future climates and abstraction regimes, and monitors the
surface and groundwater systems (especially environmentally sensitive areas), will help better
manage the resource and alleviate the impacts of climate change on agriculture, domestic
and town supplies and the environment.
It is difficult to make any valid judgements about expected changes in the localised recharge
in aquifers where it is a dominant process because localised recharge can either increase or
decrease in response to reductions in rainfall. An increase in rainfall may not affect localised
recharge because of shallow watertables and minimal storage space available to
accommodate any additional recharge. A decrease in rainfall can increase localised recharge
due to decline in watertables, thus accommodating otherwise rejected recharge.
Summary
In summary, out of the 14 priority aquifers the Otway Basin is the largest groundwater
resource with a sustainable yield of 1326 GL/year (Figure 59). The Coastal River Alluvium 4
and Coastal Sands 4 are also large groundwater resource systems, having sustainable yields
of 424 and 410 GL/year, respectively. The sustainable yield of three high-priority aquifers
(Daly Basin, Gunnedah and Pilbara) range between 329 and 357 GL/year. The Lachlan and
Coastal River Alluvium 1 are also significant groundwater resources, having sustainable
yields of 139 and 111 GL/year, respectively. The sustainable yield of the remaining six priority
aquifers is less than 100 GL/year per aquifer (Figure 59).
Groundwater use is above the sustainable yield in three priority aquifers (Upper Condamine
and Border Rivers Alluvium, Atherton Tablelands and Gunnedah). The groundwater utilisation
level is 71 and 84 per cent of the sustainable yield in the Coastal River Alluvium 4 and Pilbara
Aquifers, respectively (Figure 59). In five of the 14 high-priority aquifers the groundwater
utilisation level ranges between 42 and 60 per cent of the sustainable yield. The remaining
four priority aquifers have relatively low groundwater utilisation levels (15 to 23 per cent).
Surface water use is also above surface water sustainable yield in four high-priority aquifers
listed in Table 13. It ranges between 40 and 70 per cent in five priority aquifers. The level of
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126
1400
1200
1000
1400
1200
1000
400
400
300
300
200
200
100
100
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Agriculture
Domestic and town water supplies
Commercial and industrial
Mining
GW sustainable yield
Percent groundwater use
Figure 59: Groundwater use by agriculture and others, total use and sustainable yield of highpriority aquifers 100
80
60
40
20
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Figure 60: Groundwater use as per cent of total water extraction in high-priority aquifers
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Groundwater sustainable yield (GL)
Groundwater use (GL)
surface water use is relatively low in the remaining five high-priority aquifers. Groundwater
extraction as a percentage of total water extraction is above 80 per cent in six aquifers and
ranges between 60 and 80 per cent in four aquifers (Figure 60), showing the importance of
the resource and the dependence of agriculture and other users on groundwater supplies.
Agriculture is the largest groundwater user in priority aquifer areas, followed by domestic and
town water supplies and commercial and mining industries—except in the Pilbara where the
mining industry is the main groundwater user (Figure 59). In nine high-priority aquifer areas,
above 80 per cent of total groundwater use is for agriculture. Agriculture, domestic and town
water supplies and commercial and mining industries in these aquifer areas are all heavily
groundwater-dependent enterprises. Groundwater dependency is particularly high in the
Upper Condamine and Border Rivers Alluvium and Toowoomba Basalts aquifers.
Groundwater is a finite resource that can diminish if it is not replenished through groundwater
recharge. Groundwater recharge can occur via diffuse or localised recharge processes and
depends on rainfall. Climate change impacts on rainfall that in turn can impact on both of
these recharge processes. Diffuse recharge is the dominant process in seven of the 14
priority aquifers and localised recharge is the dominant process in six priority aquifer areas.
Both recharge processes are important in the Daly Basin aquifer (Table 14). Groundwater
storage change is highly sensitive to recharge in half of the priority aquifers.
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Table 14: Recharge, discharge mechanisms and storage dynamics in high-priority aquifers
Aquifer
Recharge
Diffuse
recharge
Adelaide
Geosyncline
3
Discharge
Surface
water
recharge
Surface
water
discharge
Evapo­
transpiration
Coastal
discharge
(seawater
intrusion)
Storage dynamics
Ground-water
supply
dependency
(extraction)
Depth to
watertable
*
Upper
Condamine
and Border
Rivers
Alluvium
Coastal
River
Alluvium 1
Coastal
River
Alluvium 4
Coastal
Sands 4
Daly Basin
Gunnedah
Lachlan
Newer
Volcanics
Otway Basin
Pilbara
Port
Campbell
Limestone
Atherton
Tablelands
Toowoomba
Basalts
* Sensitive processes are shown with shaded cells.
There is high connectivity between surface water and groundwater systems with respect to
both fluxes to and from groundwater systems in all high-priority aquifers except four (Coastal
Sands 4, Otway Basin, Port Campbell Limestone and Toowoomba Basalts). In these aquifer
systems, groundwater discharge provides the baseflow to surface water systems necessary
to maintain groundwater-dependent ecosystems and, in some cases, water extraction from
river and creek systems downstream of the groundwater discharge areas
(Table 14). Groundwater discharge to the ocean is important in five priority aquifer areas
(Coastal River Alluvium 1, Coastal Sands 4 and Coastal River Alluvium 4, Plibara, and Port
Campbell lImestone). Climate change can impact surface and groundwater connectivity, and
recharge and discharge processes to and from groundwater systems, due to changes in
shallow watertables that exist in relatively large areas in 11 of the 14 high-priority aquifers
(Table 14).
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S:R
Ratio
The projected diffuse recharge has large variation under the three future climates. Relative to
the baseline 80-year historical period, diffuse recharge is projected to increase under the wet
future climate in most aquifer areas—except Otway Basin and Port Campbell Limestone,
where it is likely to remain relatively unchanged. In seven high-priority aquifers where
localised recharge is a dominant recharge process and surface water groundwater
connectivity is high, rainfall under the wet future climate is projected to increase between 8
and 16 relative to the baseline 80-year historical period. The impact of this projected increase
in rainfall on localised recharge has not been evaluated but may not cause large reductions in
localised recharge. Localised recharge may remain either unchanged or even slightly
increase relative to the baseline 80-year historical period in these aquifer areas. No significant
changes in shallow watertables, connectivity of surface water and groundwater systems and
groundwater discharge to surface water systems are expected either. However, the impact of
climate change on localised recharge is difficult to quantify since both increases and
decreases in rainfall can cause an increase or decrease in localised recharge. Assuming the
wet future climate will not impact the localised recharge, adverse impacts on the groundwater
resource are unlikely. Therefore, no significant impacts on agriculture, water supply,
commercial and mining industries and the environment are anticipated if a climate similar to
the wet climate eventuates in the high-priority aquifer areas.
Relative to the baseline historical period, diffuse recharge under the median future climate is
likely to increase by 8 to 13 per cent in two aquifer areas, remain relatively unchanged in five
aquifer areas, reduce by 5 to 7 per cent in four aquifer areas and by 15 to 17 per cent in three
aquifer areas (Pilbara, Port Campbell Limestone and Otway Basin). Since diffuse recharge is
the dominant recharge process in the Port Campbell Limestone and Otway Basin aquifers,
reduction in recharge is expected to impact agriculture and domestic and town water supplies.
Since reduction in diffuse recharge is due to reduction in rainfall it is also likely to affect
surface runoff, flow volumes and duration in the surface water systems, and in particular may
impact localised recharge in the Pilbara aquifer area where it is the dominant recharge
process (Table 14). Some impacts on agriculture, domestic and town water supplies,
commercial and mining industries and the environment are likely in three (Newer Volcanics,
Atherton Tabelands and Adelaide Geosyncline 3) of the four aquifer areas where diffuse
recharge is the dominant recharge process, and a reduction in diffuse recharge of 5 to 7 per
cent is expected under the median future climate. Reduction of 5 per cent in diffuse recharge
is expected in the fourth aquifer area (Coastal River Alluvium 1). Localised recharge—the
dominant recharge process in Coastal River Alluvium 1—may also be impacted, but it is
difficult to quantify the effect of reduced rainfall on fluxes to and from groundwater systems.
Based on projected reductions in diffuse recharge and assuming localised recharge will have
similar trends, impacts on agriculture, domestic and town water supplies, commercial and
mining industries and the environment are likely in half of the high-priority aquifers if the future
climate is similar to that of the median future used in the analysis. No significant impacts on
groundwater-dependent industries and the environment are expected in seven high-priority
aquifer areas where the groundwater resource is likely to either remain unchanged or
increase under the median future climate.
Diffuse recharge is expected to reduce in all high-priority aquifer areas under the dry future
climate. It is likely to reduce by 14 to 18 in two aquifers (Lachlan and Daly Basin), by 40 to 55
per cent in four aquifers (Coastal River Alluvium 1, Port Campbell Limestone, Pilbara, and
Otway Basin) and by 23 to 39 per cent in the remaining eight aquifer areas, relative to the
baseline 80-year historical period. It should be noted that diffuse recharge is the dominant
recharge process in seven of the 14 aquifer areas where reduction in diffuse recharge is due
to a projected reduction in rainfall. The reduction in projected rainfall is likely to impact surface
runoff, flow volumes and flow duration in seven high-priority aquifer systems where localised
recharge is the dominant recharge process. Whether this will decrease or increase localised
recharge in these seven aquifers is difficult to ascertain due to a lack of surface water–
groundwater interaction data. The lower diffuse recharge means it is likely the decline in
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watertables can be compensated for by increased localised recharge because of the
availability of additional storage space. The lower watertables, if they occur, mean less or no
discharge to surface water systems, which will impact on GDEs and the environment.
Therefore, relatively large impacts on agriculture, domestic and town water supplies,
commercial and mining industries and the environment are likely if a dry climate similar to the
one used in this analysis eventuates. This will require an appropriate level of management
response to quantify the fluxes to and from groundwater systems under climate change, and
determination of abstraction regimes to better manage the impacts of climate change on
groundwater-dependent enterprises.
Conclusions
In this study 14 aquifers were identified as high-priority based on their importance as a
groundwater resource and their sensitivity to climate change. Following are the main
conclusions about the rainfall and recharge trends and their likely impacts on groundwaterdependent enterprises due to climate change:

Diffuse recharge is a dominant process in seven high-priority aquifers and localised
recharge is the main process in the remaining seven. Diffuse and localised recharge are
both expected to change in response to changes in future rainfall. The change in diffuse
recharge is highly variable, ranging from an increase in recharge under the wet future
climate in most high-priority aquifers to substantial and large reductions under a dry future
climate in all high-priority aquifers. There will be changes in localised recharge, but these
can’t be quantified at this time because of a lack of available information related to fluxes
to and from groundwater. The impacts of an increase or a decrease in rainfall can be either
an increase or a decrease in the localised recharge depending on the watertable depth,
surface runoff, flow duration, flow volumes and presence, and significance and degree of
surface water–groundwater connectivity.

Groundwater discharge to surface water systems is important in 10 of the 14 high-priority
aquifers where watertables are shallow in many areas. The groundwater discharge to
surface water systems is expected to reduce due to lower watertables expected under the
drier climates.

The impacts of changes in the diffuse and localised recharge on groundwater resources
and groundwater-dependent enterprises vary depending on resource utilisation and
allocation levels and per cent changes in groundwater recharge. Some groundwater
resources will increase under wetter climates whereas all decrease under drier climates.

The groundwater-utlisation level is variable across high-priority aquifers, being above the
sustainable yield in some and relatively low in others. Agriculture is the largest
groundwater user, followed by domestic and town water supplies and commercial and
mining industries—except in the Pilbara aquifer where the mining industry is the largest
user. Groundwater use as per cent of total water extraction is above 80 per cent in six
high-priority aquifers and ranges between 60 and 80 per cent in five, highlighting the
importance of the groundwater resource for various industries.
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
Impacts on agriculture, domestic and town water supplies, commercial and mining
industries and the environment are not likely under a wet future climate due to an increase
in the groundwater resource as a result of the expected increase in diffuse and localised
recharge. Under a median future climate the impacts on groundwater-dependent
enterprises and ecosystems are likely in seven high-priority aquifers due to projected
reductions in diffuse recharge and possible reductions in localised recharge. Impacts on
agriculture, domestic and town water supplies, commercial and mining industries and the
environment are expected under a dry climate due to the relatively large reductions in
diffuse recharge in a majority of the high-priority aquifers.

The relationship between aquifer characteristics, such as the degree of usage compared to
sustainable yield or the balance between surface water and groundwater usage, and the
impact due to climate change is complex and will require localised investigation and
assessment.
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6. Recommendations for groundwater
management and planning processes
to cope with climate change
Despite our water shortages, Australia’s groundwater reserves are seriously underinvestigated
—Åsa Wahlquist
This chapter discusses the project outcomes within the context of water management
practices in Australia. To fully appreciate the issues associated with climate change and its
impacts on groundwater resource management, it is important to gain a sense of how
groundwater extraction limits for GMUs are estimated and administered across Australia. The
following is a summary of those approaches.
Groundwater management in Australia is largely characterised by a focus on the
establishment of groundwater extraction limits for GMUs based on sustainable-yield estimates
for various groundwater systems. Jurisdictions adopt a variety of approaches that are largely
based on an assessment of the proportion of renewable groundwater resources that can be
abstracted for consumptive use.
Groundwater models of varying complexity have been developed for a number of aquifers,
some of which are discussed in Chapter 5. Commonly, the models have been developed for
stressed systems or aquifers with a high level of development. The models are used to
assess the impacts of various water management options on groundwater resource
availability, with the estimation of sustainable yield being the main outcome. A range of
sustainability criteria are used to derive sustainable levels of extraction, but it is not a widely
accepted practice to include environmental, social or economic criteria within the model
framework to define resource sustainability for the various water management scenarios.
There are exceptions to this approach, and these are becoming more numerous over time.
One is the Gnangara Sustainability Strategy, where environmental constraints were included
in the analysis. Water plans in the Northern Territory are also developed with an emphasis on
environmental and social constraints. The recent emphasis on environmental and social
impacts, particularly within the context of the development of the Basin Plan for the MDB,
leads to a growing awareness that existing, development-focused, water plans need to be
adjusted accordingly.
Where groundwater models are not available, and that is in the vast majority of cases,
sustainable yield assessment is commonly based on expert estimation of renewable
groundwater resources. As recharge is commonly not measured directly, this is mostly
defined as a proportion of rainfall or, in some cases, a proportion of baseflow. A constant
proportion is commonly set for an aquifer regardless of interannual variation in rainfall.
Where the proportion of baseflow is adopted as a substitute for sustainable yield definition,
the approach is based on an assumption that in balanced and closed systems, groundwater
discharge is equal to total annual baseflow in the rivers receiving groundwater and that this
discharge from the system equals recharge to the system under steady-state conditions.
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It is not a common practice to account for historical variability of climatic condition and its
effect on renewable groundwater resources and changes in groundwater demands. Further,
most extraction limits are defined for GMUs rather than at the aquifer scale.
Non-renewable groundwater resources are also allocated for use in some aquifers. In most
instances, the non-renewable nature of the resource is acknowledged and an explicit
management approach is communicated to stakeholders. Generally, the approach is to
allocate a percentage of aquifer storage over a specified time. For instance, 10 per cent of
storage might be allocated over a 200-year period.
The impact of climate change on groundwater resources provides an additional challenge for
groundwater management. As described above, current approaches to groundwater
management generally lack the sophistication to incorporate natural variability into the
estimation of groundwater extraction limits. However, climate change science is concluding
that there will be a potential for increased levels of climate variability, as well as the more
commonly acknowledged shifts in rainfall and temperature. How management will deal with
this increased level of variability presents a major challenge. Though falling outside the
project scope, it appears that there is a need to develop risk-based or adaptive approaches to
groundwater management that can account for both year-to-year variability in renewable
groundwater resources and longer-term impacts from climate change. In addition, the data
requirements to enable such an approach are numerous, and this data is currently not being
collected. Critical to this approach are fundamental datasets related, for example, to waterlevel fluctuations and the metering of groundwater extraction.
The outcomes of this report will contribute to an understanding of climate change impacts on
groundwater management, as this project fills some of the knowledge gaps related to the
possible consequences of climate change to the groundwater resource across the country.
This study has been carried out at a regional scale, considering the gross consequences at
the aquifer level and hence, can make only broad recommendations that would require
further, more detailed, analysis at a scale commensurate with the resource utilisation on the
ground.
The effect of climate change on groundwater resources is dependent on a number of factors
relating to both aquifer characteristics and projected changes in climate parameters. These
include:

the sensitivity of aquifers to climate changes

the magnitude of the climate changes, which may affect groundwater replenishment
and natural losses

the changes in groundwater demands

the changes in land use under changing climate conditions.
In addition, the relationship between renewable resources and climate across the country
may influence the magnitude of climate change impact at various locations. Thus, the spatial
and temporal variability in the response to climate change of individual aquifers may change
under differing scenarios and between similar aquifer types across different climate types.
The impact on a particular aquifer cannot be assumed to be similar to a similar aquifer in a
different location elsewhere in the country. For example, coastal alluvial aquifers in South
Australia will have a different response compared to coastal alluvial aquifers in the Northern
Territory, and these aquifers may be subject to change in behavior under climate change in
different ways.
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The following discussion relates to the process by which climate change might be
incorporated into the development of water-allocation plans.
Recharge-rainfall relationship and sensitivity of recharge to
changes in rainfall
Some water-allocation plans in Australia use a simple relationship between rainfall and
recharge to estimate the renewable groundwater resources that can be allocated for
consumptive use. An exploration of this relationship and its behaviour under a future climate
is warranted within this context. As well, the change in recharge as a function of the change in
rainfall can provide a useful indicator of future stress on the groundwater resource.
As it discussed in Chapter 4, at an individual location the relationship between recharge and
rainfall is not linear, and the proportion of the rainfall that becomes recharge decreases with a
reduction in rainfall. One of the factors influencing this relationship is rainfall intensity.
Reduction in rainfall commonly coincides with a reduction in rainfall intensity, and under lower
annual rainfall and lower intensity the proportion of rainfall that becomes recharge reduces.
This was found to be true at individual locations, at aquifer level or at the continental scale.
This is why, for example, recharge rates and their proportion in annual rainfall are the lowest
in the Bsk climate type where, in addition to low rainfall, rainfall intensity is also particularly
low. In addition to the regions with lower annual rainfall, the proportion of rainfall that
becomes recharge is low in the areas with heavier soils and with trees as a land cover
(Appendix 3).
Setting a constant percentage of rainfall as a substitute for recharge estimation is likely to
lead to underestimation of recharge during wet years and overestimation during drier years.
Another limitation of some current practice is the assumption that under a fixed percentage of
total rainfall, a per cent decrease in rainfall is translated into a corresponding per cent
decrease in recharge. However, as discussed in Chapter 4, the relationship between a
change in rainfall and a change in recharge is not as simple as a one-to-one correlation. For
the majority of soil/vegetation/climate type combinations, changes in recharge are two to four
times greater than changes in rainfall (see Figure 72 in Appendix 3). These changes may be
described as recharge elasticity, which increases in regions with low rainfall, heavy soils and
tree land cover, and are likely to be greater under conditions when a low proportion of rainfall
becomes recharge.
Future climate impacts on rainfall
It is important to understand that climate change projections have an inherent variability due
to both the different model platforms used and the future climates possible. Various climate
models can produce different results from similar initial scenarios. As a result, the analysis of
the impact of climate change on groundwater resources deals with a wide range of projected
changes in climatic characteristics, particularly rainfall. There are also limitations related to
projections of rainfall intensity changes.
The uncertainties in direction and magnitude of regional rainfall changes are pervasive and
limit our ability to provide confident assessments of likely impacts for many regions of
Australia (see Figure 5 and Figure 6 in Chapter 2). Projections are more consistent for south­
west Western Australia and the southern MDB where all GCMs project a decrease in rainfall.
Outside those regions, under wetter climate conditions the future changes in rainfall may
reach +11 per cent and +22 per cent in 2030 and 2050, respectively (see Figure 7 in Chapter
2). If a dry climate eventuates, the reduction in rainfall may be from 22 to 41per cent in 2030
and 2050, respectively. Considering recharge elasticity, such ranges in projected rainfall
changes lead to significant uncertainties in recharge estimation.
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Further advancement in climate projection and GCM downscaling techniques may allow a
reduction in the projected range of results. For instance, it was shown (see Chapter 2) that
dynamic or stochastic downscaling methods produce a smaller range of rainfall projections
than daily scaling. However, currently only the latter is readily available at a national scale
and, as such, was used in this project.
In addition to projected changes from the GCMs for rainfall and temperature across the
country, the climate-type analysis led to the identification of areas where a combined variation
in rainfall and temperature led to a change of climate-type classification. Such circumstances
may cause changes in vegetation cover or land use, which in turn may have an additional
impact on water resources.
Future climate impacts on diffuse recharge
The inherent spatial and temporal variability in groundwater recharge is likely to increase due
to projected climate change and the range in the climate change projections. The impact of
climate change on diffuse recharge is not uniform throughout the country and the projections
are highly variable. However, it was shown that the historical recharge variability (as
simulated over 15-year periods) is greater than the projected changes under the future
climate scenarios. As discussed earlier, the current groundwater management practice does
not clearly incorporate natural variability into the estimation of groundwater extraction limits.
The inability to adequately measure, and hence manage variability, historically and currently,
will be exacerbated by climate change unless improved (targeted) monitoring and evaluation
(including modelling) is undertaken. Historical variability in annual recharge may be over
several orders of magnitude, and near-future climate effects are likely to be within the range
of this variability, though long-term trends may impact low and high extremes.
As discussed, rainfall intensity has a profound effect on recharge. However, climate
projections within current GCM data downscaling at a continental scale is insufficient to
accurately predict the effect of climate change on rainfall intensity, despite overall
observations that extreme events are likely to become more frequent.
The change in recharge as a function of the change in rainfall can provide a useful indicator of
future stress. It was shown (Chapter 4) that the sensitivity of changes in diffuse recharge
relative to changes in rainfall does not seem to change significantly under different warming
scenarios. The relative importance of non-rainfall parameters, however, does seem to
increase (Figure 29) and this needs further investigation to determine what the determinant
parameters are.
A shift in the climate-type occurrence, as indicated in Chapter 2, may affect vegetation
communities and hence is likely to cause additional changes in the recharge/rainfall
relationship. There is expected to be a corresponding decrease in diffuse recharge across
these major zones. The groundwater resources that are likely to experience this additional
pressure due to climate changing from historical to a median future include: Atherton
Tablelands, Coastal River Alluvium 1, Adelaide Geosyncline, Newer Volcanics, Pilbara, Port
Campbell Limestone and Otway Basin. This is in addition to the identified substantial to very
large reductions in recharge under a dry future climate across these aquifers.
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Future climate impacts on interaction with surface water
Changes in surface and groundwater interaction may have a profound impact on availability
of both surface water and groundwater resources in many regions across Australia. Changes
in groundwater levels under future climate may affect the head difference between surface
waters and the watertable, which in turn may increase or reduce localised groundwater
recharge. In gaining rivers, groundwater systems also regularly (either perennially or
intermittently) provide baseflow to surface waters, and provide a water source to terrestrial
vegetation and to consumptive users such as surface water extractors.
Climate effects on surface and groundwater interaction may reduce the capacity to provide
such discharge under a future dry climate, hence impacting on groundwater-dependent
ecosystems. Conversely, if the future climate is wetter, relative localised recharge may
reduce, but groundwater discharge may increase due to increased diffuse recharge rates,
also impacting on GDEs and resource availability. Rising watertables can also lead to
increased problems associated with dryland salinity and potential acid sulfate soils.
Owing to the significance of local hydrological and hydrogeological conditions in surface and
groundwater interaction, the analysis of climate impacts on this interaction at a national scale
is limited. However, some outcomes of this project’s activities can provide insights to possible
impacts.
Discharge to surface water
In gaining surface water systems, groundwater discharge provides a positive feedback loop
whereby the climate change impacts on surface water features can be further amplified by the
changes in groundwater systems due to a reduction in groundwater discharge. For instance,
in Chapter 5, it was noted that most groundwater models reviewed showed a decrease in
diffuse recharge under future median and dry climate scenarios, which in turn leads to a
decrease in groundwater discharge to rivers for those modelled areas.
However, the review of the models also showed that the relationship between the reductions
in the recharge component of the various models was not linearly correlated with the
reductions in the river discharge component. That is, depending on conceptualisation of the
simulated processes in the model, the proportion of the change in diffuse recharge that was
manifest as changed river discharge ranged between none and a very high value. This
observation may be heavily influenced by the way the model recharge and discharge
processes are conceptualised. However, the relationship holds for the different climate
scenarios.
As stated in Chapter 5, the simulation of surface and groundwater interaction was one of the
least-advanced features of the reviewed models, which often adopt a simplified approach in
conceptualisation of a complex relationship between the various components of recharge and
discharge. There is a clear need for better understanding of this relationship, which may also
vary from system to system, with a view to predicting future impacts due to climate change.
But this is difficult without the aid of a complex numerical simulation of the system.
Localised recharge from rivers
In the arid and semi-arid climate zones with low rainfall, and hence low diffuse recharge,
localised recharge associated with losing rivers and flooding is known to be an important
source of renewable groundwater resources. This is also the case associated with lowland
river systems. Localised recharge is also generally more important where perennial streams
are in contact with shallow groundwater in alluvial and karstic systems.
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The analysis undertaken in Chapter 4 indicated that there are a number of river features that
may influence the level of climate change impacts on localised recharge. In addition to the
projected changes in river flow under future climate scenarios, these features include river
channel morphology, river slope, the type of losing stream (connected or disconnected) as
well as the depth to the watertable. As discussed in Chapter 4, the changes in localised
recharge due to climate change are likely to be similar to the projected changes in river flow
from disconnected losing streams, but lower than the projected changes in river flow from
connected losing streams. For both cases the impact on localised recharge is likely to be
more significant in rivers with wide and flat channels and in the lower valleys, where river
slope is small.
The sensitivity of localised recharge to changes in river flow reduces in areas with deeper
groundwater. An increase in the groundwater depth under future climate scenarios is likely to
cause an increase in localised recharge from connected losing streams even under scenarios
where reductions in river flow are projected.
However, when overbank flooding occurs, changes in localised recharge may become much
greater than that projected from variations in river flow. Some available data, such as for the
Chowilla floodplain, indicated that the changes in recharge volumes may reach up to 100 per
cent while the changes in river flow are projected to be about 20 per cent. However, the
relevant contribution of localised recharge from losing streams compared to the contribution
of localised recharge associated with overbank flooding is an area that requires further
research. Such analysis, even on a conceptual level, should be based on a prior knowledge
of river morphology. Unfourtunately, information on river morphology and flow rates
associated with flooding was not available for the gauging stations discussed in Chapter 4.
In the groundwater models reviewed, the localised recharge processes are significantly
simplified. The river is commonly modelled with changing river stage and a constant width of
the channel; changes in the effective river width under various flow conditions are not
commonly simulated. However, within the constraints of the groundwater-modelling
environment, changes in the width of computational cells for various stress periods are not
practical. In such circumstances, changes in river stage as a substitute for the changes in the
river width may be adopted, but it would require careful consideration of the magnitude of the
river stage change to accurately reflect changes in surface water and groundwater interaction.
The method described in Appendix 4 and Chapter 4 could be further used to support such an
approach. None of the models reviewed simulated recharge due to overbank flooding as a
dynamic process.
Priority aquifers
Not all groundwater systems are equally sensitive to variations in climatic conditions. It will be
the small (low-storage volume), rapidly responding, high transmissivity groundwater systems
that will feel the greatest impact of climate change. The shallow alluvial sands and karstic
aquifers that fill and spill each year will provide the earliest response to changed conditions.
These are the sensitive aquifers, but generalisations cannot be made (see Chapter 3). Thus,
we have defined aquifers that are sensitive to climate change and those that are important as
a groundwater resource. A critical subset is those that are both important and sensitive: the
high-priority aquifers (see Figure 15 in Chapter 3).
Superimposed on the distribution of priority aquifers is an assessment of the current climate
conditions determining recharge to the aquifers. From this, the priority aquifers may be
described by type and climate zone (Chapter 3). This static picture can be expanded to
include the expected response of recharge to climate change by comparing the future
recharge scaling factors (RSF) to determine where the most critical recharge zones coincide
with the critical aquifers.
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Figure 61 shows the regions where there is predicted to be the maximum change in recharge
under the future median climate scenario as measured by the RSF: the largest increase
(lower 5th percentile of RSF) and largest decrease (upper 5th percentile of RSF). The data
illustrates an aspect of climate change that is rarely considered, namely that while large parts
of the country are projected to experience drying conditions over the next 50 to 100 years,
some regions may experience wetter conditions (northern rivers of New South Wales and
possibly northern Australia). The changed climatic conditions, particularly the changed rainfall
regime, with events that have potentially increased rainfall intensity, may result in areas of
increased recharge even under a long-term reduction in rainfall amount. This observation
must be tempered, however, with knowledge of the absolute recharge amount. Thus, while
the increased RSF expected in northern New South Wales may lead to a significant increase
in actual recharge volumes, for most of the region in northern Australia displaying an
increased RSF, the historical recharge amounts are extremely low, so even a large RSF will
do little to augment existing resources. While the predominant response to future climate will
be management of reduced groundwater resources, there may, therefore, be areas where the
future may provide increased groundwater resources, or possibly excess groundwater
resources, which may lead to rising watertables and consequent risk of dryland salinity.
Considering the areas of the maximum change in RSF, an area worthy of further
consideration is identified in south-west Western Australia. These aquifers have been
incorporated into the list of priority aquifers requiring further detailed investigation, increasing
the primary list of 14 aquifers to 20 (Figure 62). These Western Australia aquifers comprise
those of the Perth Basin (North, Central and South), Collie Basin, Peel-Harvey and the
Carnarvon Basin. These additional six aquifers have been included as they have been
identified as experiencing the largest proportionate reduction in recharge under a future
climate. The aquifers comprise the sedimentary basin aquifers of the south-west Western
Australian coast. They are generally layered aquifer systems with a broad unconfined
groundwater system at the surface. Nearly all are heavily developed for urban and drinking
water supply. The effect of climate change on groundwater resources of four of these aquifers
was investigated and reported within the SWWASY project (CSIRO 2009a). It was shown that
a future climate may result in a 50 per cent reduction in recharge, which, for these responsive,
sandy aquifers, can locally cause significant watertable decline (>10 m), impacting on
groundwater-dependent ecosystems and the ability to pump the resource. Overall impacts on
total water resources, however, were estimated to be negligible due to limited impacts of
climate change on groundwater response in the areas outside the water-supply mounds
(CSIRO, 2009a). If a continued drying takes place under an extreme dry future climate,
however, a deficit of 250 GL/yr may be realised, in large part due to increased groundwater
demand as surface water resources dry up.
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Figure 61: Map showing location of extreme recharge scaling factors expected under the
future median climate scenario.
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Figure 62: Map showing location of priority, sensitive and important aquifers
Groundwater use and effect on dependent industries
Groundwater use may become an important factor that influences sensitivity of groundwater
resources to climate change. It was shown that water use in many regions largely depends on
groundwater, and the aquifers in those regions are likely to experience further stress under a
drying climate.
In the 20 aquifers indentified as high priority, based on the importance of the groundwater
resource and its sensitivity to climate change, some are heavily stressed where groundwater
use is above the sustainable yield and some have low abstraction levels. The dependency on
groundwater supply is high across most high-priority aquifers as groundwater accounts for at
least 60 per cent of total water extraction in 11 of the 14 high-priority aquifers.
Agriculture is the main groundwater user, followed by domestic and town water supplies. It is
also important to mention that groundwater abstraction for these use types is very localised.
As discussed in Chapter 6, irrigated agriculture and urban areas often cover less than 2 to 3
per cent of the aquifer’s area. As a result, the implication of climate change impact on
groundwater resources may be more severe in some GMUs than in others.
Commercial, mining and other industries also depend on groundwater resources. The Pilbara
aquifer is projected to be most impacted by climate change where historical diffuse recharge
is already lowest. However, this may be beneficial for mining dewatering activities in the
region.
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Climate change impacts on the groundwater resource will depend on the type of future
climate. The groundwater resource and groundwater-dependent industries are unlikely to be
affected if a wet climate occurs. Under a median future climate, impacts on groundwaterdependent industries and ecosystems are likely in seven high-priority aquifers due to
projected reductions in diffuse recharge and possible reductions in localised recharge.
Substantial to very large reductions in groundwater resources are expected in all high-priority
aquifers under a dry future climate. This is expected to significantly impact agriculture, water
supplies, industries and the environments.
Knowledge advancement required to better project future
climate changes on groundwater resources
One of the project conclusions was related to the need to further advance the current
knowledge of groundwater systems, and better quantify groundwater fluxes that are
particularly sensitive to climate variability, including diffuse recharge, interaction between
surface and groundwater, as well as groundwater abstraction.
This will require efforts in three related areas: 1) understanding the processes that influence
recharge in more depth; 2) quantifying the key recharge parameters on an aquifer-by-aquifer
basis; and 3) undertaking a range of scenario analyses using suitable models.
A major deficiency at the current time is a rigorous understanding of the actual recharge
volumes entering key groundwater resources across Australia, especially the ability to
rigorously simulate surface water–groundwater interactions. In most cases, current recharge
estimates are either educated guesses or are the result of model calibration where the nonuniqueness of the model process could mean a range of possible recharge estimates. More
detailed studies of recharge for the key aquifer systems are needed to reduce the level of
uncertainty.
A modelling approach to understanding future climate impacts can also be implemented in
concert with the above approach. The projection of future climate change is highly variable at
this stage, so an approach that can provide boundaries to the variability of scenarios is
required. Rather than one possible future, water-resource managers will require knowledge of
a range of possible futures—scenario modelling will deliver the envelope of possible
scenarios within which climate change adaptation can be formulated.
The only reliable method to forecast groundwater resource responses to climate change is to
undertake numerical simulation of the system, providing these systems are adequately
charaterised. However, there is a paucity of reliable groundwater models in Australia, and the
review of some models led to the conclusion that there is a need for analysis of how
applicable current groundwater models are to simulate the impacts of climate change.
The manner in which a model conceptualises key processes determines the nature of the
output from the model. In an audit of the models used in the series of CSIRO sustainableyield studies and in the MDBA work, very few models simulated sophisticated surface water–
groundwater interactions, and those that did were assessed as requiring further development.
In some models where key processes have been simulated, the groundwater response to a
future wet climate has been slightly counterintuitive in that a wetter climate led to a lower level
of interaction between streamflow and groundwater due to higher groundwater levels resulting
from higher diffuse recharge rates. It is the objectivity of a well-posed simulation that allows
these issues to be brought to the fore and considered.
Therefore, there is a major impediment to progressing an analysis of groundwater response
to climate change, which in addition to the uncertainty associated with climate models, was
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attributed to limitations in groundwater-simulation models. A key recommendation of this work
is that all groundwater models used in groundwater resource management in Australia should
undergo a climate change audit to ensure that they are fit-for-purpose when proposing climate
change adaptation strategies.
Within the context of the above discussion, Table 15 describes recommendations for
adequate management response to monitoring and assessment, tailored to high-priority
aquifers. The needs for further investigation and associated indicative costs for the highpriority aquifers are further discussed in a separate report, Summary of the costs of carrying
out further quantitative investigations in 20 priority aquifers.
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Table 15: Recommendations for the required management response, monitoring and
assessment in each of the priority aquifers
Aquifer
Resource
utilisation
level
(per cent of
sustainable
yield)
Projected diffuse
recharge
reduction under
dry future
climate
Required management response and
assessment*
1. R2 management response
2. Quantify localised recharge
Lachlan
59
18
3. Quantify fluxes from groundwater to surface
drainages
4. Monitor environmentally sensitive areas
1. R2 management response
Newer Volcanics
53
31
2. Quantify fluxes from groundwater to surface
drainages
3. Monitor environmentally sensitive areas
1. R4 management response
Upper
Condamine and
Border River
Alluvium
140
Atherton
Tablelands
103
38
2. Quantify localised recharge
3. Quantify fluxes from groundwater to surface
drainages
1. R4 management response
28
2. Quantify fluxes from groundwater to surface
drainages
1. R2 management response
Coastal River
Alluvium 1
2. Quantify localised recharge
53
43
3. Quantify fluxes from groundwater to surface
drainages
4. Monitor environmentally sensitive areas
Toowoomba
Basalts
60
39
1. R2 management response
1. R4 management response
Gunnedah
109
24
2. Quantify localised recharge
3. Quantify fluxes from groundwater to surface
drainages
1. R3 management response
2. Quantify localised recharge
Pilbara
71
55
3. Quantify fluxes from groundwater to surface
drainages
4. Monitor environmentally sensitive areas
Port Campbell
Limestone
47
40
1. R2 management response
1. R3 management response
Coastal River
Alluvium 4
2. Quantify localised recharge
84
27
3. Quantify fluxes from groundwater to surface
drainages
4. Monitor environmentally sensitive areas
Coastal Sands 4
15
28
1. R1 management response
Otway Basin
22
41
1. R1 management response
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Adelaide
Geosyncline 3
1. R1 management response
23
36
2. Quantify fluxes from groundwater to surface
drainages
1. R1 management response
2. Quantify localised recharge
Daly Basin
19
14
3. Quantify fluxes from groundwater to surface
drainages
4. Monitor environmentally sensitive areas
* Following is the description of management response levels R1 to R4:
R1:
A basic knowledge of aquifers, including their approximate extent, thickness and salinity
distribution
Monitoring for baseline water level response.
R2:
Detailed knowledge of aquifers in major borefields, supported by monitoring and modelling
Broad understanding elsewhere
Monitoring close to major abstraction centres.
R3:
Detailed knowledge of aquifers
Monitoring throughout the area
Understanding of water balance supported by recharge measurement, age dating, etc.
Determination of groundwater-dependent ecosystems (GDEs).
Regional groundwater model, supported by pumping tests, to predict the effects of increased
abstraction.
R4:
Detailed understanding of hydrogeology
Calibrated groundwater model that is able to predict the effects of abstraction
Intensive water level monitoring, especially in environmentally sensitive areas.
The impact on renewable groundwater resources is more likely to cause direct impacts on
diffuse recharge, river flow (and hence, localised recharge), diffuse discharge (and hence,
GDEs) and water demand. Climate change impacts on non-renewable resources are more
likely to be indirect through effects on water demand and localised discharge such as springs.
Impacts on non-renewable resources have not been evaluated as these impacts will be driven
by increased groundwater dependence under drier climatic conditions and hence reduced
surface water resources in most parts of the country. Use, or mining, of this fossil
groundwater needs to be explicitly acknowledged under current management schemes and
incorporated into future strategies.
Climate change is predicted to have significant impacts on the ecology of GDEs. However,
GDEs are currently poorly considered (notwithstanding the approach of the Northern Territory
and increasingly in Queensland) and, as a result, the environmental water requirement is
often difficult to define.
Adaptation to climate change is predicted to incur significant costs from increased reliance on
groundwater over surface water in some localities; increased costs of groundwater extraction
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as resources are preferentially extracted; and increased costs due to extraction of currently
non-exploitable resources that become more economic as needs increase. However,
adequate values of groundwater need to be defined.
At the detailed level, aspects of this study identified that there are deficiencies in our
understanding of groundwater systems at a national level specifically relating to:

accurate data on groundwater abstraction and to what uses that water is put

knowledge of where key recharge zones are, and representation of the depth to the
watertable in those zones

location and interaction of GDEs and other dependent ecosystems, and their sensitivity to
climate change

influence of climate change on groundwater quality, particularly overall groundwater salinity
and its effect on potential land-use category changes.
In conclusion, it is likely that climate change is an added complexity to the management of
groundwater, which is likely to increase in importance in the future.
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Appendix 1 to Chapter 2: Projections
of future climate change
Changes in average annual temperature, relative humidity and solar radiation projected for
2050 using 16 GCMs (on a 0.05° x 0.05° grid across Australia) are presented for a medium
global warming scenario (see Chapter 2 for explanation of scenarios) in Figure 63 to Figure
65. There is a large range, and thus little agreement among GCMs, in projected changes in
these climate charateristics across the 16 GCMs. .
Figure 63: Change (°C) in annual average temperature projected from each GCM for a future
climate (~2050) relative to the historical climate under a medium global warming scenario
(+1.7°C)
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Figure 64: Change (%) in annual average relative humidity projected from each GCM for a
future climate (~2050) relative to the historical climate under a medium global warming
scenario (+1.7°C)
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Figure 65: Change (%) in annual average solar radiation projected from each GCM for a
future climate (~2050) relative to the historical climate under a medium global warming
scenario (+1.7°C)
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Appendix 2 to Chapter 3: Priority
aquifers
The high-priority aquifers were identified in Chapter 3 and described further in Chapter 6. In
those chapters the aquifers are described in a broad regional scale and often include a series
of smaller aquifers that may be known locally under different names. Additionally in places,
the priority-aquifer boundaries may not align with the actual physical setting of aquifers—they
are a coarse representation of aquifers as defined by management boundaries. The list of
aquifers which were lumped for the aquifers prioritisation are given below.
Aquifer
Groundwater Management Unit
State or Territory
Adelaide Geosyncline 3
Barossa Prescribed Water Resources Area
SA
Adelaide Geosyncline 3
Broughton River
SA
Adelaide Geosyncline 3
Burra Creek
SA
Adelaide Geosyncline 3
Clare Valley Prescribed Water Resources Area
SA
Adelaide Geosyncline 3
Eastern Mount Lofty Ranges Prescribed Water Resources Area
SA
Adelaide Geosyncline 3
Gawler
SA
Adelaide Geosyncline 3
Light
SA
Adelaide Geosyncline 3
Marne River and Saunders Creek Prescribed Water Resources
Area
SA
Adelaide Geosyncline 3
Southern Eastern Mount Lofty Ranges
SA
Adelaide Geosyncline 3
Western Mount Lofty Ranges Prescribed Water Resources Area
SA
Albany
Albany
WA
Atherton Tablelands
Atherton Area A
Qld
Atherton Tablelands
Atherton Area B
Qld
Calivil
Lower Lachlan Alluvium (downstream of Lake Cargelligo)
NSW
Calivil
Lower Murray Alluvium (downstream of Corowa)
NSW
Calivil
Lower Murrumbidgee Alluvium (downstream of Narrandera)
NSW
Calivil
Campaspe Deep Lead
Vic.
Calivil
Katunga
Vic.
Calivil
Mid-Goulburn
Vic.
Calivil
Mid-Loddon
Vic.
Calivil
Mullindolingong
Vic.
Calivil
Southern Campaspe Plains
Vic.
Calivil
Upper Ovens
Vic.
Canning
Broome
WA
Canning
Canning
WA
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Canning
Canning–Kimberley
WA
Canning
Derby
WA
Central Perth Basin
Cockburn
WA
Central Perth Basin
Gingin
WA
Central Perth Basin
Gnangara
WA
Central Perth Basin
Gwelup
WA
Central Perth Basin
Jandakot
WA
Central Perth Basin
Mirrabooka
WA
Central Perth Basin
Perth
WA
Central Perth Basin
Rockingham
WA
Central Perth Basin
Serpentine
WA
Central Perth Basin
Stakehill
WA
Central Perth Basin
Swan
WA
Central Perth Basin
Wanneroo
WA
Central Perth Basin
Yanchep
WA
Coastal River Alluvium 1
Bluewater
Qld
Coastal River Alluvium 1
Bowen
Qld
Coastal River Alluvium 1
Burdekin
Qld
Coastal River Alluvium 1
Cairns Coast
Qld
Coastal River Alluvium 1
Cairns Northern Beaches
Qld
Coastal River Alluvium 1
Duck Farm
Qld
Coastal River Alluvium 1
Mossman
Qld
Coastal River Alluvium 4
Bellinger Alluvium
NSW
Coastal River Alluvium 4
Brunswick Alluvium
NSW
Coastal River Alluvium 4
Clarence and Coffs Alluvium
NSW
Coastal River Alluvium 4
Goulburn River Alluvium
NSW
Coastal River Alluvium 4
Hastings River Alluvium
NSW
Coastal River Alluvium 4
Hawkesbury Alluvium
NSW
Coastal River Alluvium 4
Hunter River Alluvium
NSW
Coastal River Alluvium 4
Karuah Alluvium
NSW
Coastal River Alluvium 4
Macleay River Alluvium
NSW
Coastal River Alluvium 4
Manning Alluvium
NSW
Coastal River Alluvium 4
Nambucca Alluvium
NSW
Coastal River Alluvium 4
Richmond River Alluvium
NSW
Coastal River Alluvium 4
Tweed River Alluvium
NSW
Coastal River Alluvium 4
Bundaberg
Qld
Coastal River Alluvium 4
Clarendon
Qld
Coastal River Alluvium 4
Cressbrook Creek
Qld
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Coastal River Alluvium 4
Pioneer
Qld
Coastal River Alluvium 4
Proserpine
Qld
Coastal River Alluvium 5
Bega River Alluvium
NSW
Coastal River Alluvium 5
Towamba Alluvium
NSW
Coastal River Alluvium 5
Tuross Alluvium
NSW
Coastal Sands 4
Bellinger Coastal Sands
NSW
Coastal Sands 4
Botany Sandbeds
NSW
Coastal Sands 4
Brunswick Coastal Sands
NSW
Coastal Sands 4
Clarence Coastal Sands
NSW
Coastal Sands 4
Coffs Harbour Coastal Sands
NSW
Coastal Sands 4
Great Lakes Coastal Sands
NSW
Coastal Sands 4
Hastings Coastal Sands
NSW
Coastal Sands 4
Hawkesbury to Hunter Coastal Sands
NSW
Coastal Sands 4
Macleay Coastal Sands
NSW
Coastal Sands 4
Manning Coastal Sands
NSW
Coastal Sands 4
Nambucca Coastal Sands
NSW
Coastal Sands 4
Richmond Coastal Sands
NSW
Coastal Sands 4
Stuarts Point Sandbeds
NSW
Coastal Sands 4
Tomago–Tomaree-Stockton Sandbeds
NSW
Coastal Sands 4
Tweed Coastal Sands
NSW
Coastal Sands 4
Farnborough
Qld
Coastal Sands 4
Fraser Island
Qld
Coastal Sands 4
Moreton Island
Qld
Coastal Sands 4
North Stradbroke Island
Qld
Daly Basin
Daly Roper
NT
Daly Basin
Darwin Rural
NT
Eyre Peninsula
Limestone Lenses
County Musgrave Prescribed Wells Area
SA
Eyre Peninsula
Limestone Lenses
Southern Basins Prescribed Wells Area
SA
Fractured and weathered
rock 2
Alice Springs
NT
Fractured and weathered
rock 2
Unincorporated Area_30000450_NT
NT
Fractured and weathered
rock 2
Unincorporated Area_30000451_NT
NT
Fractured and weathered
rock 2
Unincorporated Area_30000452_NT
NT
Fractured and weathered
rock 2
Unincorporated Area_30000453_NT
NT
Fractured and weathered
Unincorporated Area_30000456_NT
NT
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rock 2
Fractured and weathered
rock 2
Unincorporated Area_30000457_NT
NT
Fractured rock
Border Rivers Fractured Rock
Qld
Fractured rock
Condamine Fractured Rock
Qld
Fractured Rock Aquifer 1
Cook
Qld
Fractured Rock Aquifer 4
Unincorporated Area_30000316_QLD
Qld
GAB 2
GAB Cap Rock
GAB 2
Unincorporated Area_30000467_NT
NT
GAB 2
Barcaldine East Mgmt Area 13 of the GABWRP
Qld
GAB 2
Barcaldine North Mgmt Area 12 of the GABWRP
Qld
GAB 2
Barcaldine South Mgmt Area 14 of the GABWRP
Qld
GAB 2
Barcaldine West Mgmt Area 11 of the GABWRP
Qld
GAB 2
Carpentaria East Mgmt Area 6 of the GABWRP
Qld
GAB 2
Carpentaria Mgmt Area 5 of the GABWRP
Qld
GAB 2
Central Mgmt Area 16 of the GABWRP
Qld
GAB 2
Flinders East Mgmt Area 8 of the GABWRP
Qld
GAB 2
Flinders Mgmt Area 7 of the GABWRP
Qld
GAB 2
Mimosa Mgmt Area 22 of the GABWRP
Qld
GAB 2
North West Mgmt Area 10 of the GABWRP
Qld
GAB 2
Surat Mgmt Area 19 of the GABWRP
Qld
GAB 2
Warrego East Mgmt Area 18 of the GABWRP
Qld
GAB 2
Warrego West Mgmt Area 17 of the GABWRP
Qld
GAB 2
Western Carlo Mgmt Area 9 of the GABWRP
Qld
GAB 2
Western Mgmt Area 15 of the GABWRP
Qld
GAB 2
Far North Prescribed Wells Area
SA
GAB 2
Unincorporated Area—Eromanga
SA
GAB 4
Great Artesian Basin
GAB 4
Clarence Moreton Mgmt Area 25 of the GABWRP
Qld
GAB 4
Eastern Downs Mgmt Area 24 of the GABWRP
Qld
GAB 4
Mulgildie Mgmt Area 23 of the GABWRP
Qld
GAB 4
Surat East Mgmt Area 21 of the GABWRP
Qld
GAB 4
Surat North Mgmt Area 20 of the GABWRP
Qld
Goldfields
Goldfields
WA
Gunnedah
Border Rivers Alluvium
NSW
Gunnedah
Lower Gwydir Alluvium
NSW
Gunnedah
Lower Macquarie Alluvium (downstream of Narromine)
NSW
Gunnedah
Lower Namoi Alluvium
NSW
Gunnedah
Miscellaneous Alluvium of Barwon Region
NSW
NSW
NATIONAL WATER COMMISSION — WATERLINES
NSW
153
Gunnedah
Peel Valley Alluvium
NSW
Gunnedah
Upper Macquarie Alluvium (upstream of Narromine)
NSW
Gunnedah
Upper Namoi Alluvium
NSW
Humevale Siltstone
Kinglake
Lachlan
Billabong Creek Alluvium (upstream of Mahonga)
NSW
Lachlan
Mid-Murrumbidgee Alluvium (upstream of Narrandera)
NSW
Lachlan
Upper Lachlan Alluvium (upstream of Lake Cargelligo)
NSW
Lachlan
Upper Murray Alluvium (upstream of Corowa)
NSW
Lachlan Fold Belt 5
ACT
ACT
Lachlan Fold Belt 5
Coxs River Fractured Rock
NSW
Lachlan Fold Belt 5
Goulburn Fractured Rock
NSW
Lachlan Fold Belt 5
Yass Catchment
NSW
Murray Group
Angas-Bremer Prescribed Wells Area
SA
Murray Group
Coorong
SA
Murray Group
Ferries–McDonald
SA
Murray Group
Kakoonie
SA
Murray Group
Mallee Prescribed Wells Area
SA
Murray Group
Peake, Roby and Sherlock Prescribed Wells Area
SA
Murray Group
Tatiara Prescribed Wells Area
SA
Murray Group
Tintinara-Coonalpyn Prescribed Wells Area
SA
Murray Group
Kaniva
Vic.
Murray Group
Murrayville
Vic.
New England Fold Belt 4
Bulahdelah Sandstone
NSW
New England Fold Belt 4
Gloucester Basin
NSW
New England Fold Belt 4
Lorne Basin (GMU split into several aquifers across climate
zones)
NSW
New England Fold Belt 4
North Coast Fractured Rock
NSW
Newer Volcanics
Bungaree
Vic.
Newer Volcanics
Cardigan
Vic.
Newer Volcanics
Colongulac
Vic
Newer Volcanics
Glenormiston
Vic.
Newer Volcanics
Heywood
Vic.
Newer Volcanics
Lancefield
Vic.
Newer Volcanics
Spring Hill
Vic.
Newer Volcanics
Upper Loddon
Vic.
Newer Volcanics
Warrion
Vic.
North Perth Basin
Arrowsmith
WA
North Perth Basin
Jurien
WA
Otway Basin
Lower Limestone Coast Prescribed Wells Area
SA
Vic.
NATIONAL WATER COMMISSION — WATERLINES
154
Otway Basin
Padthaway Prescribed Wells Area
SA
Otway Basin
Neuarpur
VIC
Pilbara
Pilbara
WA
Port Campbell Limestone
Glenelg
Vic.
Port Campbell Limestone
Hawkesdale
Vic.
Port Campbell Limestone
Nullawarre
Vic.
Port Campbell Limestone
Yangery
Vic.
Quaternary Alluv
associated with the
Goulburn River
Alexandra
Vic.
Quaternary Sand Dune
Deposits
Tarwin
Vic.
South Perth Basin
Blackwood
WA
South Perth Basin
Blackwood–Karri
WA
South Perth Basin
Bunbury
WA
South Perth Basin
Bunbury–Karri
WA
South Perth Basin
Busselton–Capel
WA
TLA 3
Apsely
Vic.
Toowoomba Basalts
Upper Condamine Basalts
Qld
Unincorporated Area
GMW
Unincorporated Area_30000586_VIC
Vic.
Upper Condamine and
Border Rivers Alluvium
Border Rivers Alluvium (Qld)
Qld.
Upper Condamine and
Border Rivers Alluvium
Upper Condamine Alluvium
Qld
Upper Valley Alluvium 4
Bell Valley Alluvium
NSW
Upper Valley Alluvium 4
Belubula Valley Alluvium
NSW
Upper Valley Alluvium 4
Castlereagh Alluvium
NSW
Upper Valley Alluvium 4
Collaburragundry-Talbragar Valley
NSW
Upper Valley Alluvium 4
Cudgegong Valley Alluvium
NSW
Upper Valley Alluvium 5
Araluen Alluvium
NSW
Upper Valley Alluvium 5
Bungendore Alluvium
NSW
NATIONAL WATER COMMISSION — WATERLINES
155
Appendix 3 to Chapter 4: Diffuse
groundwater recharge under various
climate types
Under the same climatic conditions the difference in recharge values may vary by
orders of magnitude, depending on specific combinations of soil type and land cover.
Figure 66 and Figure 67 illustrate such effects, showing the mean recharge values
for the major climate types as well as the percentage of rainfall that becomes
recharge on an annual basis. The difference in recharge can be more than 25-fold
due to changes in land cover, i.e. vegetation, and more than 400-fold under various
soils.
Figure 67 also shows that annual recharge percentage in rainfall can vary from less
than 1 per cent under trees and low permeability soils, to more than 50 per cent
under annuals and highly permeable soils. To allow adequate analysis of climate
type on recharge, only nine combinations of soil and vegetation were chosen. These
included three vegetation type (annual, perennial and trees) and three soil types with
similar hydraulic properties. The soils were selected based on a weighted hydraulic
conductivity of approximately 0.01 m/day, 0.1 m/day and 1 m/day.
300
800
Recharge (mm)
Aw
200
200
100
100
400
200
0
0
0.01
0.10
1.00
0
0.01
0.10
1.00
300
Cfa
Recharge (mm)
Cfb
600
300
0.01
200
200
100
100
100
0
0.01
0.10
1.00
0.10
1.00
0
0.01
0.10
1.00
300
0.01
hydraulic conductivity (m/d)
BSk
BWh
1.00
Csa
200
0
0.10
300
Csb
300
Recharge (mm)
300
BSh
AP
200
200
100
100
PP
TR
0
0
0.01
0.10
1.00
hydraulic conductivity (m/d)
0.01
0.10
1.00
hydraulic conductivity (m/d)
Figure 66: Recharge as a mean value within the major climate types for various soil and
vegetation types; in legend AP–annual vegetation, PP–perennial vegetation and TR–trees
NATIONAL WATER COMMISSION — WATERLINES
156
Recharge/Rainfall (%)
100
100
Aw
75
75
50
50
50
25
25
25
0
0
0.01
Recharge/Rainfall (%)
Cfb
75
0.10
1.00
100
0
0.01
0.10
1.00
100
Cfa
0.01
Csb
75
50
50
50
25
25
25
0
0.01
0.10
1.00
0.10
1.00
75
50
50
25
25
0.01
1.00
hydraulic conductivity (m/d)
BSk
BWh
0.10
0
0.01
100
75
1.00
Csa
75
0
0.10
100
75
100
Recharge/Rainfall (%)
100
BSh
AP
PP
0
TR
0
0.01
0.10
1.00
hydraulic conductivity (m/d)
0.01
0.10
1.00
hydraulic conductivity (m/d)
Figure 67: Per cent recharge in annual rainfall as a mean value within the major climate types
for various soil and vegetation types; in legend AP–annual vegetation, PP–perennial
vegetation and TR–trees
For all analysed data, rainfall had higher relative importance than other climate
characteristics. The rainfall importance in recharge estimation reduces under lower
annual rainfall conditions and was found to be lowest for areas with annual rainfall of
400 to 450 mm (Figure 68). As a result, the relative importance of rainfall is the
lowest for arid climates and particularly for climate type Bsk. When annual rainfall is
lower than 400 mm, it appears that the relative rainfall importance increases, e.g. for
desert-climate types. At the same time, the reduction in annual rainfall and its relative
importance leads to an increase in recharge sensitivity to other climate parameters
considered in this study (Figure 69).
NATIONAL WATER COMMISSION — WATERLINES
157
Annuals
Perenials
Trees
Aw
BSh
BSk
BWh
Cfa
Cfb
Csa
Csb
1.0
Ri (rainfall)
k = 0.01
0.8
0.6
0.4
0.2
0.0
1.0
Ri (rainfall)
k = 0.10
0.8
0.6
0.4
0.2
0.0
1.0
Ri (rainfall)
k = 1.0
0.8
0.6
0.4
0.2
0.0
0.0
0.3
0.6
0.9
1.2
1.5 0.0
0.3
Mean annual rainfall (m)
0.6
0.9
1.2
1.5 0.0
Mean annual rainfall (m)
0.3
0.6
0.9
1.2
1.5
Mean annual rainfall (m)
Figure 68: Relationship between relative importance of rainfall and mean annual rainfall
0.4
Annuals
Ri (other)
0.3
Trees
Perenials
Aw
BSh
BSk
BWh
Cfa
Cfb
Csa
Csb
0.2
0.1
0.0
0.0
0.2
0.4
0.6
Ri (rainfall)
0.8
1.0 0.0
0.2
0.4
0.6
Ri (rainfall)
0.8
1.0 0.0
0.2
0.4
0.6
0.8
1.0
Ri (rainfall)
Figure 69: Relationship between relative importance of temperature, VPD and solar radiation
(cumulatively) and mean annual rainfall for soil with K~1 m/day
NATIONAL WATER COMMISSION — WATERLINES
158
Reflecting the high importance of rainfall in recharge estimation, the correlation is strong
2
between rainfall and recharge for the majority of cases; R >0.7 for 82 per cent of cases of
soil/vegetation/climate type combinations. The strongest correlation between recharge and
annual rainfall is in the areas with high annual rainfall typical for tropical savannah (climate
type Aw), and temporal climate types without a dry season (climate type Cf) (Figure 70).
Correlation between rainfall and recharge becomes weaker under climate types with overall
lower annual rainfall (approximately less than approximately 700 mm). Arid climate types,
particularly Bsk, are characterised by the overall weakest relationship. Correlation between
rainfall and recharge is generally weakened under perennial vegetation and trees and under
soil with lower permeability.
Annuals
Perenials
Trees
1.0
0.6
R2
k = 0.01
0.8
0.4
0.2
0.0
1.0
0.6
R2
k = 0.10
0.8
0.4
0.2
0.0
1.0
Aw
BSh
BSk
BWh
Cfa
Cfb
Csa
Csb
0.6
R2
k = 1.0
0.8
0.4
0.2
0.0
0.0
0.3
0.6
0.9
1.2
Mean annual rainfall (m)
1.5 0.0
0.3
0.6
0.9
1.2
Mean annual rainfall (m)
1.5 0.0
0.3
0.6
0.9
1.2
1.5
Mean annual rainfall (m)
2
Figure 70: Changes in the correlation coefficient ( R ) of recharge/rainfall relationship and
mean annual rainfall within the major climate types
NATIONAL WATER COMMISSION — WATERLINES
159
As expected, a stronger correlation between rainfall and recharge was found when the per
cent recharge in annual rainfall is high, suggesting lower uncertainties in recharge estimation
based solely on rainfall data. High uncertainties should be expected in areas with a lower
percentage of recharge in rainfall, such as climate types Bsk, Bwh and Cfa (Figure 71).
Annuals
Perenials
Trees
100
Aw
BSh
BSk
BWh
Cfa
Cfb
Csa
Csb
R/P (%)
k = 0.01
80
60
40
20
0
100
R/P (%)
k = 0.10
80
60
40
20
0
100
R/P (%)
k = 1.0
80
60
40
20
0
0.0
0.3
0.6
0.9
1.2
Mean annual rainfall (m)
1.5 0.0
0.3
0.6
0.9
1.2
Mean annual rainfall (m)
1.5 0.0
0.3
0.6
0.9
1.2
1.5
Mean annual rainfall (m)
Figure 71: Relationship between per cent recharge in annual rainfall and mean annual rainfall
within the major climate types
NATIONAL WATER COMMISSION — WATERLINES
160
For 75 per cent of the soil/vegetation/climate type combinations, the sensitivity of recharge to
changes in rainfall varies between 2 and 4, indicating a 20 per cent to 40 change in recharge
for a 10 per cent change in annual rainfall (Figure 72). The relatively higher values in average
recharge elasticity were estimated for desert and arid-climate types.
Annuals
Perenials
Trees
10
Recharge Elasticity
k = 0.01
8
6
4
2
0
10
Recharge Elasticity
k = 0.10
8
6
4
2
0
10
Aw
BSh
BSk
BWh
Cfa
Cfb
Csa
Csb
Recharge Elasticity
k = 1.0
8
6
4
2
0
0.0
0.3
0.6
0.9
1.2
Mean annual rainfall (m)
1.5 0.0
0.3
0.6
0.9
1.2
Mean annual rainfall (m)
1.5 0.0
0.3
0.6
0.9
1.2
Mean annual rainfall (m)
Figure 72: Recharge elasticity and mean annual rainfall within considered climate types for
perennial vegetation and soil with K~1 m/day
Despite an overall high correlation between recharge and annual rainfall, it is commonly
weaker than the correlation between recharge and the sum of high-intensity rainfall on an
annual basis. A number of parameters that can potentially be used to assess high-intensity
rainfall on an annual basis were considered (Barron et al. 2010). The highest overall
correlation was found to be between recharge and moving average daily rainfall over 14-day
or 21-day intervals, with daily thresholds of 5 mm aggregated on an annual basis. These
values account simultaneously for high-intensity rainfall and prolonged periods of relatively
smaller rainfall events.
In addition, it was found that aggregated 95th percentile daily rainfalls on an annual basis
show better correlation with recharge than 99th percentile daily rainfalls. When rainfallintensity thresholds were considered, daily rainfall greater than 20 mm aggregated on an
annual basis also provided a better correlation with recharge than total annual rainfall.
NATIONAL WATER COMMISSION — WATERLINES
161
1.5
In general, rainfall intensity gradually reduces from north to south of the country along with the
proportion of recharge in annual rainfall (Figure 73). This is particularly evident under annual
vegetation.
0
(a)
(b)
(c)
Latitude (degrees South)
10
20
30
40
50
0.0
0.2
0.4
0.6
Phigh/P (%)
0.8
1.0 0.0
0.2
0.4
0.6
Phigh/P (%)
0.8
1.0 0.0
0.2
0.4
0.6
0.8
Phigh/P (%)
Figure 73: Changes to per cent of high intensity rainfall in total annul rainfall from north to
south of the continent: a) daily rainfall greater than 20 mm; b) moving average over 14 days
with daily 5 mm threshold; and c) moving average over 21 days with daily 5 mm threshold
Episodic recharge is defined as infrequent significant recharge events (Zhang et al. 1999).
The word ‘significant' refers to the relative magnitude of the recharge. It is, therefore, the
distribution of these events that determines the patterns of recharge (Figure 74). Episodic
recharge was estimated using statistical analysis of the modelled daily recharge data, and the
distribution of recharge events was compared with distribution of the recharge volumes
associated with those events.
The relationship between the frequency of various recharge events and associated volumes
is indicative of the episodic recharge when most of the recharge (in volume terms) is
associated with the least frequent of the recharge events. Under such assumption it appears
that, with a specific combination of soil and vegetation, the episodic recharge may take place
under the majority of investigated climatic conditions. The exceptions are related to
particularly high rainfall areas in the tropics (climate type Aw) and in the south-west under a
temperate climate with dry, warm summer (climate type Csb) and the south-east in a
temperate climate without dry season and with warm summer, where rainfall is greater than
700 mm.
NATIONAL WATER COMMISSION — WATERLINES
162
1.0
40
40
BWh
Aw
30
Frequency
Frequency
30
20
20
10
10
0
0
0.0001
0.001
0.01
0.1
1
10
100
0.0001
0.001
0.01
0.1
1
10
100
Recharge (m/d)
Recharge (m/d)
Recharge events
Recharge events
Recharge volumes
Recharge volumes
Figure3574: Example of daily recharge event and recharge volume distributions indicating
Aw
episodic recharge
Recharge volume
30
Aw
BWh
25
20
Appendix 4 to Chapter 4: Effect of
climate change on localised recharge
15
10
5
0
0
10
20
30
Recharge
events
Because of the specifics
of localised
recharge (discussed in Chapter 1) and the difficulties in
its estimation, the assessment of changes in localised recharge under changing climate
conditions on a national scale has been attempted on a conceptual basis. Other NWC
projects are designed to improve current knowledge of the interaction between surface and
groundwater. On completion of these projects, the assessment of changes in localised
recharge under changing climate conditions can be further advanced. Here, the main goal
was to define how changes in river flow under future climate scenarios may influence
changes in localised recharge. Estimation of recharge values was not included in the scope of
the analysis.
A number of observations have been made for describing how recharge is affected by stream
geometry and soil type. For example, Bouwer (1969) suggests that the infiltration flux
stabilises if the depth to groundwater is greater than twice of width of the stream. Osman and
Bruen (2002) have assessed the main factors influencing stream–aquifer seepage for a losing
stream and suggest that aquifer material properties strongly affect seepage-flow rates in all
stages of steam–aquifer relationships (especially when stream disconnects from aquifer).
They conclude that seepage from a disconnected stream cannot be determined correctly
unless the saturated hydraulic properties of the aquifer and clogging layer and the stream
water level are known.
Brunner et al. (2009) state that if the groundwater table below a stream is deep enough,
changes in the groundwater table position effectively do not change the infiltration rate. This is
termed losing disconnection (Figure 75). They have shown that for a given aquifer thickness
and river width, the depth to groundwater where the system disconnects is approximately
proportional to the stream depth and the hydraulic conductivity of the streambed sediments,
and is inversely proportional to the thickness of these sediments and the hydraulic
NATIONAL WATER COMMISSION — WATERLINES
163
conductivity of the aquifer. In the absence of other information about factors affecting
recharge, this study takes river flow as the main indicator of seepage from a streambed.
The recharge associated with a losing connected river is largely defined by the difference in
hydraulic heads between river stage and the groundwater table, hydraulic properties of the
riverbed and river morphology (river stage and the effective river width). In a losing
disconnected stream the main factors that define the localised recharge are the riverbed
properties, which control the suction potential and unsaturated hydraulic conductivity of
streambed. Overall, it was suggested that the rates of localised recharge from a disconnected
river are mostly independent of river stage, and recharge volumes are controlled by the
effective river width. In addition, the rate of water loss from a river remains constant after a
certain depth to groundwater is reached.
The change in recharge within an individual river reach for connected rivers is given by the
changes in river stage and effective river width occurring as a result of the river-flow variation.
It is also influnced by changes in the depth to groundwater. For a losing disconnected river,
alteration in localised recharge is defined by changes in the effective river width and, to some
extent, by changes in groundwater depth.
Figure 75: Example of connected and disconnected groundwater system (Source: Brunner et
al. 2009)
NATIONAL WATER COMMISSION — WATERLINES
164
In this analysis the effect of changes in river flow under future climate scenarios was
estimated for connected rivers, and some outcomes of the analysis were further inferred for
disconnected rivers.
Historical and projected future river-flow data for ‘losing’ rivers within the MDB were selected
as listed in Table 16. The data was derived within the CSIRO MDBSY project (CSIRO 2008d)
using the Integrated Quantity-Quality Model (IQQM), a hydrologic modelling tool developed by
the NSW Government for planning and evaluating water resource management policies.
Method
The adopted methodology is summarised in Figure 76, showing that the analysis was based
on simultaneous calculation of Manning’s and Darcy’s equations. The former allowed
estimation of the river stage (Hr) for a range of daily river flows and river widths (b) (Figure
77), assuming that the riverbed is characterised by a trapezoidal shape with steep banks (10­
to-1).
Two other parameters, the riverbed slope, and Manning’s coefficient can be obtained from
published data (DECC undated) and remain unchanged for individual river reachs. A range of
river slopes were used for calculations, but it was considered that river slopes of 0.0001 and
0.0005 are typical for lower and upper valleys in the River Murray region (DECC undated).
As information on river morphology was largely unavailable, it was decided to provide results
for a range of river widths. This range varied between rivers, dependent on the ranges in river
flows, but the smallest river width was 2 m and the greatest 1000 m.
Table 16: List of gauging stations along the losing streams underlain by the priority aquifers.
Some of the stations are outside of the priority aquifers.
Station
no.
Region
Location
Underlying aquifer
410001
Murrumbidgee
Murrumbidgee River at Wagga Wagga
Lachlan
416026
Border Rivers
Reedy Creek at Dumaresq
Gunnedah
418032
Gwydir
Tycannah Creek
Gunnedah
419012
Namoi
Namoi River at Boggabri
Gunnedah
419027
Namoi
Mooki River at Breeza
Gunnedah
419039
Namoi
Namoi River at Mollee
Gunnedah
419049
Namoi
Pian Creek at Waminda
Gunnedah
420004
Macquarie–Castlereagh
Castlereagh River at Mendooran
420005
Macquarie–Castlereagh
Castlereagh River at Coonamble
421023
Macquarie–Castlereagh
Bogan River at Gongolgon
421039
Macquarie–Castlereagh
Bogan River at Neurie Plains
422015
Condamine–Balonne
Brenda Gauge
422025
Barwon–Darling
Barwon River at Tara u/s Namoi Junction
Gunnedah
422358
Condamine–Balonne
Chinchilla Weir
Upper Condamine
422394
Condamine–Balonne
Condamine River at Elbow Valley
Toowoomba Basalt
Gunnedah
Darcy’s equation was used to define the rate of water losses from a unit length of a river (1
m). Calculations were undertaken for a range of river widths (at the water level at Hr) and river
NATIONAL WATER COMMISSION — WATERLINES
165
stages, identified during the first step of analysis for each river-flow rate (Figure 78). The
thickness of riverbed deposits and their hydraulic properties, though important for recharge
estimation, were assumed to be unimportant when the differences in recharge are
considered. Constant values were assigned for sediment thickness (L = 1 m) and hydraulic
conductivity (K = 0.001 m/day).
The depth to groundwater (Hgw) here is a depth below the riverbed. In the calculations, the
hydraulic gradient was defined as I = (Hr + Hgw)/L. In the first instance it was assumed to be
constant between the scenarios. This was followed by an analysis of changes in depth to
groundwater under future climate scenarios.
River flow (Q)
Manning's equation
Q
Defining the range of river stage
(Hr) and effective width (b) for the
identified flow rates
(see Figure 77)
1 23 12
R S
n
S =0.001-0.0001 (river slope)
n = 0.04 (Manning's coefficient)
R is the hydraulic radius (trapezoidal
channel with 1:10 bank slope)
Localised recharge
from unit length of a
losing connected river
Darcy's Low
R
Defining the range of recharge
(R) for identified flow (Q)
(see Figure 78)
k
b( Hr  Hgw)
L
L =1 m (thickness of bed sediments)
k = 0.01 m/day (hydraulic
conductivity)
Defining the changes in recharge
(dR) for changes in river flow (dQ)
for each combination of Hr and b
(see Figure 79)
Hgw= 0.5 - 6 m (depth to watertable
below river bed)
Flow data as FDC
for various
climate scenarios
(see Figure 34a)
Changes in river flow under the
projected future climate
scenarios (see Figure 34b)
Defining the changes in river flow
and recharge under future climate
scenarios (see Figure 80)
Figure 76: Method flow chart
NATIONAL WATER COMMISSION — WATERLINES
166
Figure 77: Relationship between river flow and river stage under for a range of river widths
Figure 78: Relationship between recharge and river flow for a range of river widths
NATIONAL WATER COMMISSION — WATERLINES
167
The change in recharge (dR) due to the changes in river flow (dQ) was further estimated for
various combinations of river widths and river stages (Figure 79). The results indicate that
under the same changes in river flow, dR is smaller for narrower rivers (lower lines in Figure
79) and greater for a rivers with a greater effective width (upper lines in Figure 79). This
indicates that dR is sensitive to river morphology.
The results of the anlaysis are reported as e=dR/dQ, describing a sensitivity of localised
recharge to changes in river-flow conditions.
The method is based on a number of assumptions. Steady-state conditions are assumed for
each of the flow rates, which is not likely to be the case during events with a fast change in
river flow and hence river width and river stage. It is also assumed that the hydraulic
properties of river sediments (or floodplain soil) are constant within the entire river width,
which is unlikely to be the case, particularly during flooding. As will be shown further, river
morphology plays an important role in e = dR/dQ, but information on river cross-sections was
not available for analysis. Some consideration of the effect of river morphology was given in a
selected case, where a composite trapezoidal river section (channel and floodplain) was
adopted.
Though simplified, the approach allowed for the examination and illustration of the general
relationships between changing localised recharge and river flow, and the effect of various
parameters that influence this relationship.
Figure 79: Per cent changes in recharge for various river widths under changes in river flow
(green lines are related to an individual river widths shown on Figure 77 and Figure 78, with
the lowest line associated with the smallest width; the red line indicates the same river flow)
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Results
The results of analysis are shown in Figure 80. The range of dR, identified as an area
coloured in green, is due to variations in the river width. The greater changes (dRmax) are
likely to occur if the changes in the river flow are predominantely associated with changes in
the effective width of the river.
Overall, the change in localised recharge from losing streams is less than the projected
change in river flow (within the set of parameters used for these calculations). The results of
this analysis, presented as a relationship between localised recharge sensitivity e = dR/dQ
and historical river flow, are shown in Figure 81, which also shows the relationship between e
= dR/dQ and historical exceedence probability. For flat river reachs, the sensitivity of the
recharge to change in river flow is overall higher. It also increases for extreme flow events
and reduces for low flow rates. A series of lines in the plots of Figure 81 are related to the
various depths to the groundwater table Hgw (1 m, 2 m, 3 m, 4 m, 5 m and 6 m), assuming
that Hgw does not change under future climate scenarios. The results indicated that the
sensitivity of localised recharge to changes in river flow reduces when the groundwater table
is lower.
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Figure 80: Changes in the river flow (red line) and the range of changes in localised recharge
(shown as a green area) for dry, median and wet future climate scenarios for all considered
stations (as listed in Table 16)
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410001
0.6
0.5
dR/dQ
0.4
0.3
0.2
0.1
0
0
20000
40000
60000
80000
100000
120000
140000
River flow, ML/day
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
0.6
0.5
dR/dQ
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
Exceedance, %
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
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422025
1
0.9
0.8
0.7
dR/dQ
0.6
0.5
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0.1
0
0
10000
20000
30000
40000
50000
60000
70000
80000
River flow, ML/day
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
1
0.9
0.8
0.7
dR/dQ
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
River flow, ML/day
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
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422015
0.9
0.8
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dR/dQ
0.6
0.5
0.4
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5000
10000
15000
20000
25000
30000
35000
River flow, ML/day
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
0.9
0.8
0.7
dR/dQ
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
Exceedance, %
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
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421023
0.9
0.8
0.7
dR/dQ
0.6
0.5
0.4
0.3
0.2
0.1
0
0
5000
10000
15000
20000
25000
30000
River flow, ML/day
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
0.9
0.8
0.7
dR/dQ
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
Exceedance, %
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
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422358
1
0.9
0.8
0.7
dR/dQ
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20000
40000
60000
80000
100000
River flow, ML/day
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
1
0.9
0.8
0.7
dR/dQ
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
Exceedance, %
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
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419039
1
0.9
0.8
0.7
dR/dQ
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20000
40000
60000
80000
100000
120000
140000
160000
River flow , ML/day
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
1
0.9
0.8
0.7
dR/dQ
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
Exceedance, %
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
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422394
0.8
0.7
0.6
dR/dQ
0.5
0.4
0.3
0.2
0.1
0
0
20000
40000
60000
80000
100000
120000
140000
River flow, ML/day
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
0.8
0.7
0.6
dR/dQ
0.5
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
Exceedance, %
1 m Max
1 m Min
2m Max
2m Min
3 m Max
3 m Min
4 m Max
4 m Min
5 m Max
5 m Min
6 m Max
6 m Min
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Figure 81: Relationship between localised recharge sensitivity e = dR/dQ and river flow
(upper) and
e = dR/dQ and flow exceedence probability (lower) under historical climate conditions (for
selected stations, as listed in Table 16). The results are given for various depths to
groundwater, which are assumed to be constant between historical and future climate
scenarios
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Localised recharge associated with floods (Chowilla
floodplain)
Flood-related recharge was identified as the major recharge mechanism for a
number of aquifers. However, the data required for recharge estimation in the areas
of the major groundwater resources is limited. Chowilla floodplain was considered
because of the availability of a sufficient dataset. This allowed estimating potential
localised recharge under various flooding events, along with the change in frequency
of these events under future climate scenarios. However, it is acknowledged that
groundwater use in this region is limited because of high groundwater salinity.
Therefore, this analysis is only illustrative.
The Chowilla anabranch region, located approximately 50 km east of Renmark at the
borders of New South Wales, South Australia and Victoria (Chapter 4), is a floodplain
of the River Murray. The climate is semi-arid with an annual rainfall around 260 mm
and potential evaporation of approximately 2000 mm/year. The topsoil found on the
floodplain is typically grey, cracking alluvial clay up to 5 m deep (Coonabidgal Clay)
overlying the alluvial sand of the Monoman Formation, an unconfined aquifer of up to
30 m depth (Jolly et al. 1993). Underlying this are the Pliocene sands, a layer that is
also unconfined and thought to be in hydraulic contact with the Monoman Formation.
Hence, regional groundwater systems can both discharge into and receive recharge
from the network of streams that cut through these layers across the floodplain.
The distribution of vegetation types on the floodplain is largely determined by the
availability of fresh water and the landform elements that have been shaped by
periodic flooding and deposition/erosion processes (Hodgson 1993). Open black-box
woodlands are the dominant vegetation type, but red-gum woodlands are found in
the riparian zones close to permanent stream channels. Generally, the groundwater
is too saline to support black box and red gum trees but some areas receive enough
flushing from flood events to support them. Therefore, the combination of flooding,
groundwater depth and groundwater salinity largely control the composition and
health of vegetation at Chowilla. Much of the vegetation is degraded because of high
soil salinity and changes in flood frequency caused by river regulation.
The extent of the Chowilla floodplain inundation was estimated using the River
Murray Floodplain Inundation Model (RiM-FIM), which links recorded river flows at
regulation points (locks) to the spatial extent of flooding derived from satellite imagery
(Chapter 4, Overton et al. 2006). This allowed examination of the extent of inundation
under given flow rates and estimation of the volume of recharge that would occur
under historical and future climate scenarios. The extent of the area considered for
this analysis was approximately 200 km2. Recharge rate zones (Chapter 4) derived
from soil, vegetation, elevation and satellite data for the Chowilla floodplain were
used as the basis for recharge volume estimation (Howe et al. 2007).
Comparing the flow-duration curves shown in Figure 82 with the inundation map in
Chapter 4 (Figure 46), it can be seen that the inundation area given by floods greater
than 100 000 ML/day (green, yellow and red colours) has a probability of less than 1
per cent under historical climate, and 0.5 per cent and 1.4 per cent under dry and
median future climate scenarios, respectively.
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The observed flow data suggests that the area of inundation for Chowilla floodplain
increases from 7 per cent for a yearly flood (one-year return period) of 30 000
ML/day to 25 per cent for a flood of one-in-five-year return period (75 000 ML/day).
These areas of inundation have changed over time at this station, such that the one­
in-10 year flow calculated in 2009 was 30 per cent less than those calculated using
historical data in the baseline scenario of ~138 000 ML/day for a one-in-10-year flow
(Doody et al. 2009), resulting in a smaller inundation area.
1000000
historical
Flow (ML/d)
100000
median
wet
10000
1000
0
10
20
30
40
50
60
70
80
Probability of flow greater than (%)
90
100
Figure 82: Flow duration curve for Chowilla daily river flow (426510) for historical, future
median andwetclimate scenarios
Combined consideration of the extent of the floodplain inundation for various daily flow rates
(from 30 000 ML/day, with 10 000 ML/day increments) and the range of daily recharge rates
within the inundated area allowed estimation of daily recharge volumes under various flow
conditions. Based on the inundation duration, the total recharge volumes were further
calculated for the range of flow rates (Figure 83).
Based on river FDC for historical data and future median and dry climate scenarios (Chapter
4), the frequencies of flow rates used in the recharge anlaysis were estimated. Using the
projected frequencies of flow events, the associated recharge volumes were plotted similarly
to FDC, but showing ‘recharge’ duration for future median and dry climate scenarios (Chapter
4). Finally, the change in recharge volume under future climates was estimated (Figure 48). It
appears that the changes in localised recharge associated with flooding are much greater
than the projected changes in river flow.
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60000
Recharge, ML
50000
150
40000
30000
100
20000
50
10000
0
30000
Inuntation area, km2
200
0
80000
130000
180000
Fiver flow, ML/day
Recharge, ML
Area, km2
Figure 83: Changes in the inundation area and associated average recharge under various
river flows
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Changes relative to historical climate, %
150
100
50
0
0
5
10
15
20
25
-50
-100
-150
Exceedance probability, %
dR_median
dR_dry
dQ_median
dQ_dry
(a)
Changes relative to historical climate, %
100
50
0
0
5
10
15
20
25
-50
-100
Exceedance probability, %
dR_median
dR_dry
dQ_median
dQ_dry
(b)
Figure 84: Projected changes in recharge volumes (dR) and river flow (dQ) from floodplain
inundation for future median and future dry climate scenarios relative to historical climate: a)
based on floodplain data; b) based on the method described in Figure 76.
As discussed earlier, this difference is likely to be associated with a significant increase in
river width during flood events, with smaller changes in river stage. The application of the
method for estimating localised recharge changes is also shown in Figure 84(b). This was
estimated using the composite trapezoidal river cross-section. However, the method
described in Figure 76, in its current state, does not account for changes in the hydraulic
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conductivity across a floodplain. Though the changes in localised recharge shown on both
plots of Figure 84 are not identical, they do show similar trends: changes in localised recharge
associated with overbank flooding are likely to be significantly greater than changes in river
flow under future climate scenarios.
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