Risks to Murray-Darling Basin Water Resources Program
Project Summary
Project code:
CD2B
Project title:
Modelling the impacts of climate change on aquatic ecosystems of the
Murray-Darling Basin
Project timeline:
Completed August 2010
Contractors:
Australian Rivers Institute, Griffith University
Report Authors:
Fran Sheldon, Stephen Balcombe, Samantha Capon, Wade Hadwen &
Mark Kennard, Nick Marsh, Nick Bond
Project objectives:
Climate change has been identified as having a substantial impact on water availability in the MurrayDarling Basin with a suggested decrease in future mean annual rainfall; ~2030 relative to ~1990 of
about 2 percent in the north of the MDB to 5 percent in the southern regions. This project aimed to
explore the impact of predicted climate change on key aquatic ecosystems of the Murray- Darling
Basin, and its specific objectives were to:
1. Review the broad literature on the predicted impacts of climate change drivers (temperature,
precipitation, UVB radiation) on aquatic ecosystems and on specific faunal groups (fish,
riparian vegetation and aquatic macrophytes).
2. Provide a synthesis on the predicted impacts of climate change on Australia and in particular,
the Murray-Darling Basin using the scenarios provided.
3. Provide a synthesis of environmental tolerances and predicted climate change impacts using
conceptual models for major ecosystem components in the Murray- Darling Basin, namely
fish, riparian and floodplain vegetation and other faunal groups
4. Provide example case studies for three regions within the Murray-Darling Basin (Dryland
Rivers, Northern Uplands and Darling Tributaries) outlining changes in habitat availability for
major ecosystem components modelled on the Best Climate Change Scenario of 2030.
Methods:
In this study a review of the literature on predicted impacts of climate change drivers was undertaken
with analysis provided of likely temperature, precipitation and UV-B radiation impacts on aquatic
ecosystems. The work then considered the implications of these predicted impacts for Australia and
the Murray-Darling Basin using the three Risk Assessment Program, agreed climate change scenarios:
1. A ‘most favourable 2030 scenario’ that is based on a continuation of the long-term (1895 to
2006) averages for rainfall and runoff across the MDB,
2. A ‘medium 2030 scenario’ that is based upon the medium global warming scenario and
associated rainfall and runoff described in the CSIRO report Water Availability in the
Murray–Darling Basin of October 2008, and
3. A ‘least favourable 2030 scenario’ that is based upon the actual climate of the MDB in the
period 1997–2006 (this includes 15% less rainfall and 50% less runoff in the southern MDB
when compared with the long-term average).
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CD2B Project Summary
Conceptual models were developed for key ecosystem components, namely, freshwater fish, riparian
vegetation, aquatic and emergent plants, and waterbirds. An example of one of these conceptual
models is provided below:
Conceptual models were also developed at a more detailed species level for freshwater fish, with text
only discussion of further impacts on riparian vegetation, aquatic and emergent plants, and waterbirds.
These conceptual models were used as the basis upon which more detailed quantitative modelling of
habitat availability under different watering scenarios is undertaken.
The steps in the modelling process were as follows:
1) Identifying ‘ecosystem components’: These are individual species or communities such as
vegetation communities which are heavily water dependant.
2) Building models: Defining the water requirements of each of these ecosystem components
represented as a quantitative model that relates flow, depth or area to habitat availability and
is described in terms of the magnitude, duration, timing, frequency and rate of change of the
hydrology.
3) Key Sites: Selecting key locations in the landscape which act as barometers of impact in so
much as they are areas of national or international ecological significance or are
representative of particular type of ecological community.
4) Flow scenarios: Obtaining flow scenarios that represent different climate change scenarios for
each of the key locations.
5) Data pre-processing: Transforming the flow data into equivalent area of inundation time
series to apply to water dependant ecosystem components.
6) Model running and data interpretation: Apply the flow scenarios to each of the ecosystem
components at each of the key locations.
A separate Methodology Report was used to discuss the modelling process step by step. The final
component of the work was the drawing together of the conceptual and quantitative models into three
regional case studies – Dryland Rivers, Northern Uplands and Darling Tributaries. The modelling
approach used for the case studies can be expanded to allow further expansion of the results to other
locations within the basin, and the running of new scenarios in future years when they become
available.
Summary of Key Results
There is considerable evidence provided in the Final Report for this project that demonstrates the
sensitivity of aquatic ecosystems to climate change due to the high heat capacity of water and indirect
effects through changes to catchment processes. Climate change drivers such as increases in water
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CD2B Project Summary
temperature and evaporation, as well as changes in precipitation, will influence the flow regime of
inland systems which, in turn, will impact on channel form and water chemistry. These changes flow
through to habitat availability and water chemistry changes that impact upon species distributions,
abundance and ecosystems processes. Changes in precipitation, temperature and evaporation will also
influence the stratification of many inland water bodies, with increased periods of high water
temperature potentially leading to stronger and more sustained periods of water body stratification.
An increase in UVB-radiation is also a potential driver of change, owing to its unknown impacts,
particularly in places of high irradiance in floodplains and inland rivers.
In the Final Report a discussion is provided of the ecological tolerances and broad climate change
implications for the key species that occur within the Basin. Amongst the fish of the Murray-Darling
Basin, some are predicted to increase their range and abundance under climate change scenarios while
others will be disadvantaged. Based on the available literature and studies to date, it is likely that the
Murray Cod, Flathead Gudgeon, Hardyhead, Australian Smelt, Macquarie Perch, Southern Pygmy
Perch Trout Cod, Two-spined Blackfish and River Blackfish will be negatively impacted as a result of
increase water temperature, disruptions to life cycle and loss of habitat. Those fish predicted to
expand and increase are Carp Gudgeons, Bony Bream, Hyrtl’s Tandan, Eel Tailed Catfish and
Yellowbelly. The predicted increase is based on the ability of these fish to cope with higher
temperatures, dry spells and altered flow regimes. The Final Report provides a full page discussion
on each of these fish with conceptual models also provided of key responses to climate change drivers
species by species.
Climate change impacts on river red gum are most likely to manifest themselves through changes in
the frequency and magnitude of floodplain inundation events. In areas where trees and forests are
already stressed by water resource development, the increased stress associated with further
reductions in flooding may be enough to cause mass death of red gums. Increased duration of dry
spells along with higher temperatures may also reduce survivorship amongst recruiting seedlings.
In contrast, climate change as depicted by the current scenarios, is unlikely to have major impacts on
black box woodland. In fact a decrease in the frequency and duration of flooding across floodplains
in the MDB, combined with higher air temperatures, may well allow an increase in the range of black
box, it being already well adapted to higher air temperatures and reduced flooding. Like black box,
lignum stands are unlikely to be negatively impacted by climate change, although, there is a greater
likelihood of negative impacts in the less frequently flooded regions of the MDB, where higher air
temperatures combined with reduced rainfall may cause declines in health and habitat value of the
species.
Grasslands, rushes, cumbungi and sedges are all likely to be impacted by reduced frequency and
duration of flooding, combined with lower soil moisture affecting seed / rhizome germination and
survival rates. Typha stands may extend in certain regions of the MDB as warm, nutrient rich
conditions may result in maximum growth. However, where water levels and soil moisture are
reduced and the periods between flooding extended, Typha stands will disappear.
Zooplankton and freshwater mussels are the other faunal groups considered in the study, with both
being adversely impacted by higher temperatures placing them at thermal risk. For zooplankton the
reduced floodplain inundation associated with water abstraction is likely to have reduced diversity and
reproductive capacity and, as a result, reduced the productivity of floodplains when flooding does
occur.
The predicted impacts of climate change form the basis for the development of quantitative models.
These models are used to provide a ‘picture’ of three case study regions in the MDB: dryland regions,
northern uplands and Darling tributaries. A brief overview of these case studies is provided:
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CD2B Project Summary
Dryland Rivers
The Dryland rivers region includes the Paroo River and Warrego Rivers and their associated
tributaries in the northwest of the Murray-Darling basin. These rivers are essentially unregulated with
no major water abstractions. On the Warrego there are some low level weirs and minor levels of water
abstraction, the Paroo is “free flowing” with no formal structural barriers and only minor water
abstractions for stock and domestic supply.
The predicted consequences of the considered climate change scenarios for the dryland rivers are
relatively mild. The median of the predicted daily maximum temperature change is 1.50C and the
change in flow volume for the best estimate 2030 climate is 6.7%. The frequency of flooding of the
lower Warrego area including Yantabulla swamp is not predicted to change significantly under the
considered climate change scenario. For the best estimate climate change scenario, models predict an
18% decline in the mean annual habitat score for River Red Gum Woodland maintenance conditions
and smaller reductions (13-16%) in the annual habitat availability for bird breeding events. The interannual variability in habitat availability is high under the current climate, and would be likely to
increase under a future warmer climate, although the project was unable to test this hypothesis with
the current data sets.
In the absence of flow regulation or water abstraction the predicted climate change impacts on these
rivers are probably within the response capacity of the fauna and flora, and therefore there is likely to
be no major changes in distribution and abundance.
Northern Uplands
The Northern Uplands region includes upper reaches of the Condamine River to St George and the
upper reaches of the Border Rivers, including the Macintyre River, Weir River and Moonie River.
The predicted consequences of the considered climate change scenarios for the Northern Upland
rivers are relatively mild. The median of the predicted daily maximum temperature change is 1.50C
and the change in flow volume for the best estimate 2030 climate is 11%. The frequency of flooding
of the Condamine at St George is not predicted to change significantly under the considered climate
change scenarios.
The major impacts on the fauna and flora of the rivers in this region of the Murray-Darling Basin are
associated with water resource development, namely reduced flooding frequency due to water
abstraction. In the absence of flow regulation or water abstraction the predicted climate change
impacts on these rivers are probably within the response capacity of the fauna and flora, and therefore
there is likely to be no major changes in distribution and abundance related specifically to climate
change. However, the combined impact of reduced flooding as a result of water resource development
and higher air temperature, higher evaporation, lower local rainfall and lower humidity associated
with climate change may have severe impacts on the productivity potential of the associated lowland
floodplains of the Condamine-Balonne system (eg. Culgoa floodplain, Narran Lakes complex).
Reductions in the viability of zooplankton resistant stages and also the seedbanks of floodplain plants
could have drastic foodweb impacts on the fauna associated with rivers and reliant on the “boom”
capacity of floods for long term population survival (fish and waterbirds).
Darling Tributaries
The Lowland sections of the northern Darling tributaries (Gwydir River, Namoi River, Macquarie
River, Mehi River, Castlereagh River and Bogan River) are influenced by some headwater storages,
small scale regulating structures (in-channel low level weirs) and large scale water abstraction for
irrigation.
The predicted consequences of the considered climate change scenarios for the Darling Tributaries are
relatively mild. The median of the predicted daily maximum temperature change is 1.50 and the
change in flow volume for the best estimate 2030 climate is 8.2%. The frequency of flooding of the
Darling Tributaries area including Macquarie Marshes is not predicted to change significantly under
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CD2B Project Summary
the considered climate change scenario. For the best estimate climate change scenario the project
predicted a 27% decline in the mean annual habitat score for River Red Gum Woodland maintenance
conditions and even larger reductions (33-36%) in the annual habitat availability for bird breeding
events. The inter-annual variability in habitat availability is high under the current climate, and would
be likely to increase under a future warmer climate, although the study was unable to test this
hypothesis with the current data sets.
The major impacts on the fauna and flora of the rivers in this region of the Murray-Darling Basin are
again associated with water resource development, namely reduced flooding frequency due to water
abstraction. In the absence of flow regulation or water abstraction the predicted climate change
impacts on these rivers are probably within the response capacity of the fauna and flora, and therefore
there is likely to be no major changes in distribution and abundance related specifically to climate
change. However, the combined impact of reduced flooding as a result of water resource development
and higher air temperature, higher evaporation, lower local rainfall and lower humidity associated
with climate change may have severe impacts on the productivity potential of the associated
floodplains and terminal wetlands. Reductions in the viability of zooplankton resistant stages and also
the seedbanks of floodplain plants could have drastic foodweb impacts on the fauna associated with
rivers and reliant on the “boom” capacity of floods for long term population survival.
These three case studies provide useful insights into likely climate change impacts at a broad regional
level. The case studies were chosen because hydrological data was available to input into the models.
Seven case studies remain to be completed once the researchers have access to hydrological
modelling data for those regions.
Comparisons with other Projects:
The important interaction between climate effects and water resource development, described by this
project, is also identified by project CS1. Even small in-stream or floodplain structures, as well as
significant water abstraction, when combined with climate effects, can have significant and
cumulative impacts on floodplain and aquatic ecosystems. Project CS1 provides a thorough discussion
of the management implications and steps needed to assess the potential effects of such development.
Knowledge Gaps Identified
The key knowledge gap identified through this research is the lack of easy-to-access hydrological
data. The failure to access this information has significantly hindered this project as the hydrological
data is a vital input for the quantitative models. It is also worth noting that the discussion throughout
this report is quite broad and general. Long-term studies will be required of the different fish, plant
and waterbird species discussed in the Report to assess the true extent and impact of climate change.
Implications for Policy
The Final Report for this project is easy to read and the conceptual models provide useful
diagrammatic representations of the likely impacts of climate change on predicted species. This
means that the Report could be used to inform policy makers about the latest thinking on climate
change and how it will impact on different parts of the Basin. A note of caution, however, as many of
the predictions are for relatively little change in many areas and this could downplay the need for
resources to be allocated to communities (both ecological and human) to be able to adapt to ongoing
climate change impacts.
Recommended Communication Approach:
Two reports have been submitted for this project, both incomplete as a result of the lack of access to
hydrological data. The first is the Methodology Report and the second the Final Report. In the Final
Report the literature review and discussion about climate change impacts is informative and worthy of
being made widely available. This could be done in combination with those parts of the Final Report
that cover the discussion of the predicted impacts on species and the associated conceptual models.
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CD2B Project Summary
In terms of the Methodology Report, it would be sensible to hold off on publishing this until the full
modelling has been done with the recent hydrological data for all regions of the Basin. This is
because it is far better to provide a complete picture of the results rather than a smaller subset of the
three case studies currently provided. It would also be interesting to put the results of the modelling
work out to further peer review to see if there is any further insights or information about the fish,
plant, waterbird and other faunal species, that could be added to the knowledge gathered to date.
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CD2B Project Summary