Risks to Murray-Darling Basin Water Resources Program
Project Summary
Project code:
CD2A
Project title:
Impacts to Water Quality in the Murray-Darling Basin arising from
Climate Change
Project timeline:
Completed September 2010
Contractors:
Sinclair Knight Merz
Report Authors:
Bonnie Bonneville, Julie Morris, Emma Collins, David Dettrick and
Annie Sanderson
Project objectives:
This project examines water quality impacts from extreme events induced by climate change in the
Murray-Darling Basin (MDB). Extreme climate events by definition have a low frequency of
occurrence, however, when they occur they can have major consequences for water quality in rivers
and water storages. Extreme climate events often cause extreme responses in water quality, for
instance, unprecedented nutrient and suspended solids loads following bushfires or major floods. One
of the anticipated effects of climate change is the increase in both the frequency and intensity of
extreme weather events. Many of the drivers of these events are linked to climate-related variables
that are predicted to intensify under climate change. If this occurs, then the effect will be an increase
in the frequency and intensity of extreme events, and potentially a change in their distribution in the
landscape. Water quality impacts from extreme events may compromise the availability and
suitability of the MDB’s water resources for its beneficial uses. The objective of this study was to
assess the risks to the water quality values in the Murray-Darling Basin under four climate scenarios:
a. ‘Wet extreme’ (wet extreme scenario and associated modelled rainfall and runoff
b. ‘Return to normal’ (continuation of long-term averages 1895-2006 for rainfall and runoff)
c. ‘Median 2030’ (median global warming scenario and associated modelled rainfall and runoff
d. ‘Dry extreme’ (actual climate experienced during 1997-2006, including 15% less rainfall and
50% less runoff)
The scope of the project included both the northern and southern parts of the Murray-Darling Basin
and addressed:
1. Water quality trajectories in main-stem rivers in each of the MDB regions based on ‘end-ofvalley’ sites;
2. Water quality trajectories for 1-2 examples of iconic wetlands, drinking water reservoirs,
irrigation infrastructure and groundwater aquifers; and
3. General water quality impacts from ‘extreme events’ (e.g. bushfires, heat waves, prolonged
drought, heavy precipitation events, intense tropical cyclones and dust storms).
The interaction between events, i.e. intense rainfall following bushfires and/or prolonged drought, was
also to be considered.
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CD2A Project Summary
Methods:
The approach taken by the consultants was to describe the relationship between extreme climate
events and water quality impacts. A Literature Review is provided that underpins the Final Report
and explores the potential impacts to water quality arising from climate change. The conceptual
understanding and regional knowledge documented in the Literature Review provides the necessary
background information to feed into the risk assessment phase as detailed in the Final Report. An
assessment of risk was conducted for each of the following ‘extreme events’ - bushfires, heat waves,
prolonged drought, heavy precipitation events, intense tropical cyclones and dust storms. For each of
these events the following outputs are provided in the Final Report:
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A conceptual model for water quality impacts;
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The key water quality variables affected and their expected trajectories;
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Severity and longevity of the water quality impacts;
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The potential consequences to ecosystem values (e.g. aquatic ecosystem, drinking water,
recreation, irrigation);
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A description of regions within the MDB that would be most at risk; and
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The potential frequency within the MDB of the extreme events (where information is
available).
Summary of Key Results
The Literature Review provided as part of this report is comprehensive and covers the key drivers of
water quality in rivers and reservoirs. It also synthesises the direct and indirect impacts of climate
change on water quality through the use of Tables that split information and discussion between
northern Basin and southern Basin regions. Conclusions are drawn about the implications of climate
change on surface water quality, with impacts occurring directly through increasing surface
temperatures, and indirectly through changes in catchment hydrology and surrounding land-use. The
consultants note that both the Dry Extreme and Wet Extreme 2030 climate change scenarios present a
risk to water quality in rivers, reservoirs and wetlands in the MDB.
Groundwater was also considered, with the consultants reporting that the impacts on groundwater
resources is likely to be delayed and subdued, relative to the impacts on surface water resources. This
is because groundwater systems are more susceptible to long-term trends and, in some cases, have a
large volume of water in store to act as a buffer to such changes. The Final Report goes on to say that
in the short term the most significant impacts of climate change on groundwater quality in the MDB
are likely to be in relation to dryland salinity and river salinity. In the longer term, however, change
could be positive, as reduced precipitation and increased evapotranspiration could lead to the lowering
of watertables and a reduction in saline groundwater discharge to rivers.
These impacts are further discussed in a series of case-studies that link directly to water quality
monitoring sites in the MDB. Case studies are provided for: Barwon-Darling, Border Rivers,
Campaspe, Condamine-Balonne, Goulburn-Broken, Gwydir, Lachlan, Loddon, MacquarieCastlereagh, Moonie, River Murray, Murrumbidgee, Namoi, Ovens, Paroo, Warrego and WimmeraAvoca. Each of these case studies is two-to three pages long and provides an overview of regional
water quality issues, key values (for example, environmental, water supply, recreation etc), threats
(for example, stock grazing, road crossings, sedimentation) and a summary of possible water quality
impacts. A table is provided for each case study that analyses historical data on water quality and
provides trajectories for each water quality parameter (pH, salinity, turbidity, total nitrogen, dissolved
oxygen and temperature) during wet and dry extremes. The table also shows some potential
consequences for the regional water quality dependent values (for example, environmental, water
supply and recreation).
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CD2A Project Summary
The Final Report provides a good introduction to climate change impacts and then focuses in detail on
each of the five extreme events outlined in the project objectives. For each of these extreme events a
detailed discussion is provided about likely climate change impacts on water quality. This is
summarised in a matrix that ‘maps’ the intensity of the event, the geographical area of the Basin
affected and whether the impact of the event is likely to be ‘high’, ‘medium’ or ‘low’. In addition, a
detailed reference list is provided for each of the ‘extreme event’ chapters and is an excellent resource
for anyone wishing to delve deeper into the research findings and discussions contained in the Final
Report. Key findings for each of the extreme events follow.
Prolonged Drought:
Climate change projections generally suggest that rainfall will decrease, and temperatures will
increase over the MDB in the future. The projections of drought occurrence under climate change
show clearly increasing trends, particularly driven by a significant increase in the areas of the Basin
affected by extreme hot temperatures. While the relationship between hot temperatures, precipitation
and runoff remains unclear, it is apparent from observational data that recent temperature increases in
the Basin have occurred in conjunction with increasingly severe reductions in runoff and water
availability. The land and water management practices in an area (e.g. levels of diversion,
groundwater use and catchment pollutant loads) will also affect the impacts of rainfall reductions and
increased temperatures for a particular area. These findings are summarised in the risk assessment
table below:
Heat Waves:
Heat waves are usually associated with the El Nino-Southern Oscillation, which brings a hotter and
drier climate. The term is relative to the usual weather in the area. The combination of little to no
wind, low humidity and unimpeded sunlight can heat up a given location to temperatures significantly
higher than normal. This excessive heat and low humidity is collectively known as a heat wave. As
the future climate is predicted to be hotter, it is anticipated that heat waves will become more intense,
longer lasting and/or more frequent. Whilst no clear evidence is available, there is concern that higher
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CD2A Project Summary
water temperatures will lead to increased pathogen survival in the environment. Predicted effects of
heat waves and higher temperatures are:
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Decreased oxygen-carrying capacity of waters;
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Lower dissolved oxygen through higher rates of organic matter mineralisation;
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More intense stratification, warmer epilimnion relative to the hypolimnion
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Increased evapotranspiration and decreased volume of water (increased nutrient and pollutant
concentrations particularly from point sources);
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Invasion by temperature-tolerant exotic species, such as carp;
Based on the results of past investigations, there are a number of factors that influence the risk of heat
wave occurrence and associated water quality impacts. Most important is the location of a waterway
within the MDB i.e. the southern part of the Basin is at greater risk than the northern Basin. It is also
important to consider other local factors such as the orientation of a waterway and whether riparian
vegetation is well established and provides shading. The ecological assets of the waterway must also
be considered as some species are more susceptible to heat waves than others. The following matrix
applies a risk rating to heat wave occurrence across the MDB.
Flooding (including tropical cyclones):
Extreme flood events, soil erosion, aquifer recharge and rising water tables may result from increases
in heavy rainfall. Such impacts can have severe implications for humans and the environment,
particularly in the MDB where rivers are already under stress as a result of river regulation. Intense
rainfall events can result from a number of different weather conditions. Two causes of increased
flood potential are intense precipitation events and tropical cyclones. The latter is less common in the
MDB, however the consultants argue that it should be considered given the potential water quality
impacts that arise from post-cyclone flooding, and the potential for an increase in the intensity of
cyclones as a result of climate change.
The projected changes in rainfall intensity have been modelled on the projected increases in
temperature (CSIRO 2006). For example, an increase in temperature of 1 C would result in a 10 –
20 % increase in the intensity of extreme daily rainfall in NSW, but a 6 % decrease in extreme daily
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CD2A Project Summary
rainfall in Victoria. In contrast, an increase in temperature of 5 C or more may result in a 25 %
increase in extreme rainfall in Victoria. With respect to changes in cyclone events, CSIRO (2006)
referred to a study undertaken by McInnes et al. (2003) which projected a 5 – 10 % increase in
tropical cyclone wind speeds and a 20 – 30 % increase in tropical cyclone rainfall if temperatures
increased by 2 – 3 C. These projections indicate that there is an increased risk to the water quality of
Australian rivers with a higher frequency and likelihood of blackwater events, waterborne illnesses
(mosquito), sedimentation and turbidity.
According to CSIRO and Bureau of Meteorology (2007) there will be an increase in extreme
precipitation events in the southern MDB, however the northern MDB is less likely to be affected by
such events. However, the northern MDB may be influenced by post-cyclone flooding arising from
more intense tropical cyclones in northern Australia. The impacts from such events may include
erosion from strong winds and water quality impacts of post-cyclone flooding. A risk matrix
summarises the potential impacts of extreme rainfall events and tropical cyclones on water quality.
Bushfires:
Although the relationship between climate and fire is confounded by factors such as arson and fire
management, it is clear that hotter and drier years have greater fire risk. The future climate of south
east Australia under global warming is likely to lead to an increase in fire frequency and severity.
Several studies have found that fire weather will increase with the expected changes in climate.
Increases in fire weather are likely to occur due to an increase in temperature, decrease in rainfall,
decrease in relative humidity, increase in wind, increase in storms with lightning and an increase in
the number of extremely hot days.
The likelihood of water quality impacts that arise from these extreme bushfires also depends on
subsequent rainfall. The timing and intensity of rainfall events post bushfire within a catchment
governs the transport of contaminants into the waterway. A large rainfall event post-fire may cause
extremely high total suspended solids, organic carbon, total nitrogen and total phosphorus loads to
move into the waterways. The intensity of the fire is also related to water quality, because at high
temperatures (i.e. 200 to 400 °C), nutrients from burned organic matter (i.e. plant material) are either
lost as gases, or converted (mineralised) into forms that are more readily transported by surface runoff
or drainage water (e.g. nitrate). The risk matrix illustrates the potential impacts of extreme bushfire
events on water quality.
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CD2A Project Summary
Dust Storms:
A dust storm is defined as an area of raised dust that moves within the prevailing wind system. Dust
particle sizes peak at 1000 μm (10-6 m) and range down to very small particles finer than 1 μm. Air
quality has been measured using the particulate matter (PM) 10 μm and recently the PM 2.5 μm scales
to indicate possible environmental health impacts, with current thinking that particles less than PM
2.5 are harder for the human body to filter, and constitute a higher health risk. A dust storm is formed
when wind speeds are high enough to dislodge, suspend and then lift dust particles into the
atmosphere. In Australia, the minimum wind speed required to generate dust storms is around 30
km/h. Dust storms have been detected to a height of 4.5 km into the atmosphere and average 1-2 km
in height, being transported by lower level climate winds locally and then upper level wind climate
systems over longer distances.
Large areas of Australia experience frequent sand and dust storms, and these events are a feature of
desert and arid soil zones globally. There is evidence that dust storms influence global processes of
marine and freshwater nutrient flux and ecosystem processes such as seasonal oceanic algal blooms.
In Australia, the availability of dust for wind erosion transport is related to soil dryness, and
vegetative ground cover. Prolonged droughts, which dry surface soils and the associated reduction in
ground cover experienced in the arid zone, can combine with dry and unstable air to create conditions
likely to generate dust storms. These conditions may be created by global weather systems such as El
Nino climate cycles and will therefore be affected by climate change. Seasonally, summer and spring
produce the conditions of both dry and unstable air conditions at ground level most likely to create
major dust storms that can travel over sufficient distance to reach coastal areas and major cities. The
arid zone areas centring around the Simpson Desert and the Channel Country experience the largest
number dust storms per annum, with summer and spring dryness and wind creating the best
conditions for dust storms during the year.
The frequency of dust storms under climate change scenarios for the MDB will be related to the
predicted change in drought frequency (temperature and rainfall) and wind speed, as these are the key
variables related to the likelihood of dust storms occurring. The risk of dust-storm related water
quality impacts is highest in the low rainfall areas in the arid zone within the MDB. This includes the
northern Paroo, Warrego and lower Barwon-Darling regions and parts of the lower Murray region. In
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CD2A Project Summary
these regions the rainfall is low and variable and the vegetation cover is poor. The soil types are also
conducive to dust-storms. The risk to water quality is during the first flush rainfall event post-dust
storm. The dust storms can affect 100’s of kilometres and therefore the impacts to water quality may
be far reaching. The lowest risk areas are the southern high rainfall areas within the MDB. This
includes regions such as the Ovens, Goulburn-Broken and Upper Murray. In these areas the
landscape is well-vegetated, either with native forests or pasture and as a result, has a low likelihood
of generating dust storms.
The Final Report concludes with a table summarising the high and low risk areas within the MDB for
extreme events and their key drivers.
Comparisons with other projects
This work complements that of Project CD2B Impacts of Water Quality on Aquatic Health, with
findings from both pieces of work building an interesting picture of the future in the MDB in different
regions. The social and economic studies conducted as part of Projects CD1 and CDC2 can also be
added to this project to discuss wider societal impacts of climate change. Impacts of fire on catchment
water yield are considered also in projects CP1 and CP2.
Knowledge gaps identified:
This study is based on a number of quite recent research findings and predictions from organisations
such as the CSIRO and the BoM. While this research is well regarded, a commonly acknowledged
issue for those working in climate change prediction is that there is considerable uncertainty in the
climate change predictions of Global Climate Models (GCMs) particularly at the scale of the MDB.
This uncertainty arises from the different processes incorporated in the GCMs and the different ways
in which the processes are modelled. Best estimates of future climate change (OZClim 2010 CSIRO )
under a high Greenhouse Gas emissions scenario (IPCC 2000) (currently being tracked globally), for
2030 and 2100 are listed and illustrated for Australia and interpreted for the MDB in the Final Report.
Implications for Policy:
Both the Literature Review and Final Report offer excellent summaries of current knowledge and
thinking about likely climate change impacts in the MDB. It would be useful to draw the findings
from this work together with the other Risk Assessment projects to provide a policy briefing for
Commonwealth and State decision makers.
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CD2A Project Summary
Recommended Communication Approach:
It would be useful for the Literature Review and Final Report to be published and made widely
available as they are good platforms to start discussions around the impacts of climate change in the
MDB and the many different parts of the community, both ecological and human, that these impacts
can affect.
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CD2A Project Summary