think climate. think change.
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|Australian landscapes, biodiversity and agriculture reflect one of the most variable rainfall and stream flow patterns in the world.
Growing water demand and climate change present major water resource management challenges for Australians. Impacts of climate change on water are of particular significance, given that Australia is a naturally dry continent and because water is essential for survival, for the economy and for our way of life. This is exacerbated by major spatial differences in runoff and water demand that mean that water resources are currently fully or over-utilised in several important regions.
| Potential Direct impacts | Potential Indirect impacts |
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| Increases in temperature and reduced rainfall (in most of southern and eastern Australia) | |
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| Increases in temperature and increased rainfall (over much of north-western Australia) | |
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| Sea level rise | |
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| Altered frequency of extreme weather events | |
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Changes in rainfall combined with increased potential evaporation are expected to result in reduced runoff across most of Australia. In some cases reductions could be be severe. For example by 2050 average streamflow is projected to drop 7-35% in Melbourne, 10-25% in the Murray-Darling Basin and 31% in the Stirling catchment (WA).
These estimates of future impacts are consistent with regional observations in recent decades. In southwest WA, mean rainfall has declined dramatically from the late 1960s, in a series of steps. However reduction in river flows, and hence dam inflows, has been magnified nearly threefold from the reduction in mean rainfall. An average rainfall decline of 10-20% caused a 40-60% decline in dam inflow (Fig. 1).
Figure 1: Stepwise changes to dam inflows, Perth
Source: WA Water Corporation www.watercorporation.com.au/D/dams_streamflow.cfm
Both rainfall deficits and droughts are projected to become more extreme due to climate change. Climate models suggest that drought could be as much as 20% more common by 2030 over much of Australia and up to 80% more common in south-western Australia by 2070. The economic impact of these climatic conditions is significant. The cost to the Australian economy from the 2002-2003 drought was estimated as $6.6 billion.
Climate change is likely to increase the stress on rivers already under pressure from salinity, over-allocation and declining water quality. Higher water temperatures and reduced stream flows will tend to adversely affect water quality - water temperature, oxygenation, nutrient and pollution loads, salinity and other water chemistry - affecting habitat values for aquatic and riparian species and affecting human uses. Drought conditions are likely to exacerbate erosion and downstream sedimentation. Higher sediment loads enter rivers following extreme rainfall events or extreme bushfire events, both of which are projected to increase with climate change. Changed climatic conditions are also likely to produce conditions that favour riparian and aquatic weeds and algal blooms.
Increases in extreme rainfall events are projected for many regions, although the impacts are spatially variable. Increased extreme rainfall events are likely to result in more flash flooding, strains on sewerage and drainage systems, and challenges for emergency services.
