Climate change and Sydney's water balance
The CSIRO has advised the NSW Government that, in the future, the Hawkesbury-Nepean catchment is likely to be between 0.2°C and 1.6°C warmer and evaporation is likely to increase by between one per cent and eight per cent by 2030. Work is under way to better understand impacts on average rainfall.
This advice relates only to the Hawkesbury-Nepean catchment at a broad scale. To improve our understanding of how climate change could impact water availability and water demand in greater Sydney, additional work has been commissioned. This work is being undertaken through a major collaboration between the CSIRO, State and Commonwealth Government agencies and the University of NSW.
While the results of the research will not be available until late 2008, the evidence to date suggests there will be increased variability in rainfall patterns, placing Sydney at risk if we rely solely on rainwater stored in dams. Investing in measures such as desalination and recycling reduces our dependency on rainfall. This will provide a supply of water that is not climate dependent, to help ensure that Sydney is better able to deal with severe drought and the potential impacts of climate change on our water supply system.
Isn't it already known that climate change is going to dry up the dam catchments?
Projections of future climate change recently provided by CSIRO to the NSW Government of the Hawkesbury-Nepean catchment (which provides most of Sydney's drinking water) do not clearly indicate whether yearly rainfall across the catchment is likely to decline. However, as it is likely that evaporation will increase, CSIRO's advice indicated that the catchment will have a tendency to be drier in the future, and that rainfall is likely to be more variable, with longer dry periods followed by heavier rainfall events.
It is recognised that the impact of climate change on our stored water supplies will depend on the time of year that most rain falls in the future and whether the ground is already wet due to earlier rain. Also, the demand for water could be different under a changed climate. To better understand these questions, further work specifically targeted to Sydney has been commissioned.
The current uncertainty about the specific impacts of climate change increases the importance of ensuring that non-rainfall dependent strategies such as desalination and recycling are available to Sydney, to supplement water stored in Sydney's 11 major dams.