Recent declines in southern Australian rainfall: a review of recent science

Australia's rainfall is highly variable, and has been characterised by extended periods of drought, interspersed by very wet years, over the last 100 years of climate records. The presence of such high rainfall variability makes the detection and attribution of longer term changes to regional rainfall a difficult task.

Currently, seasonal rainfall deficiencies have existed in south-western Australia (SWWA) for the past 30 years and in south-eastern Australia (SEA) for the past 14 years. In both regions, long term rainfall deficiencies equate to a 15% reduction in autumn and winter season rainfall. While recent drought in the Murray Darling Basin region of the continent has been comparable to the so-called World War II and Federation (circa 1900) droughts, the prolonged decline of autumn rainfall in SEA is perhaps without historical precedent. For SWWA, the last 30 year period of reduced winter rainfall is unprecedented in the historical record.

To date, a number of studies have investigated the significance and potential causes of drought in southern Australia. In general, this body of work points to naturally occurring drought superimposed on longer term rainfall declines, potentially associated with climate change. However the partitioning of such attribution has proved difficult.

We present a summary of relevant research in this area, including the evidence for potential proximate and ultimate causes of the current rainfall declines. These include the influence of the El Nino Southern Oscillation and the Indian Ocean Dipole, changes to local tropical sea surface temperatures, changes in local pressure and the sub-tropical ridge, and changes in southern hemisphere autumn and winter storm activity and prevailing weather systems.