Australia has undergone periods of low rainfall and high rainfall that last for decades.
The shift between such periods often appears as a step change. For example, the eastern half of Australia was drier from 1895–1948 and wetter from 1948–1976. Rainfall has been below average across much southeast Australia since 1997, with the Murray-Darling Basin experiencing below average rainfall since 2002.
The Bureau of Meteorology has found in 2009, serious to severe rainfall deficiencies occurred in a narrow band extending along the coast from southern New South Wales through Gippsland to south-central Victoria.
In addition, very long-term rainfall deficiencies persisted across parts of southern and eastern Australia.
Lower rainfall and reduced runoff in the southeast of Australia associated with the current drought is in part due to natural variability as well as to human-induced climate change. The relative contribution of each of these mechanisms remains uncertain.
The moisture deficit associated with drought is also the result of higher temperatures.
Temperatures in Australia have risen by about 0.9 °C since 1910 and there is a high level of scientific confidence that anthropogenic greenhouse gas emissions are a major driver of this increase in temperature.
The current drought is unusual in that it is associated with both an intensification of the Subtropical Ridge and a high frequency of positive Indian Ocean Dipole (IOD) events.
Both of these factors are associated with reduced rainfall over south eastern Australia.
Climate change modelling shows that an intensification of the Subtropical Ridge can only be achieved when anthropogenic greenhouse gases are included in the models.
Climate model projections for the coming decades indicate an increasing risk of below average rainfall for southern and eastern mainland Australia, higher temperatures and evaporation, and below average runoff. In particular there is a significant projected increase in frequency of extremely hot years and extremely dry years.
CSIRO research into the causes of the rainfall decrease in the Murray-Darling Basin is being conducted through the South East Australian Climate Initiative (SEACI) – a partnership involving Australian and State governments, CSIRO and the Bureau of Meteorology.
CSIRO's research is helping Australia respond to the challenges and opportunities of climate change by:
- contributing to a better understanding the science of climate change
- looking at ways to mitigate and reduce greenhouse gas emissions
- preparing for and adapting to climate change impacts that are now unavoidable.