Issued 3 September 2007

Very dry since late autumn in parts of southern Australia

The late autumn and winter has been very dry over parts of southern Australia, particularly in Western Australia and South Australia. For some areas it is the second rainfall deficient winter in successive years, with winter rains being suppressed in 2006 by an El Niño event. At the yearly time-scale, rainfall deficiencies are evident in all states and territories, with the exception of the Northern Territory. As August 2007 was generally wetter than August 2006 in the areas with twelve-month rainfall deficiencies, there was a slight easing of these deficits compared with the situation at the end of July.

3-month rainfall deficiencies

For the 3-month period from June to August 2007, an area of serious to severe rainfall deficiencies covered much of SA, the far southwest corner of Queensland, far western NSW and parts of northwest Victoria. Also affected were parts of southwest WA, western Victoria and north-central Tasmania. Several regions had record low winter totals, the most notable being near Ceduna on SAs west coast.

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4-month rainfall deficiencies

Rainfall deficiencies for the 4-month period from May to August 2007 were widespread across the southwest of Western Australia. In South Australia they were evident along and inland of the west coast and Eyre Peninsula, as well as in a narrow zone extending from Port Pirie to near the SA/NSW/VIC tri-state border.

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12-month rainfall deficiencies

For the 12-month period from September 2006 to August 2007, zones or regions of rainfall deficits existed near the southwest and west coasts of WA (generally south of Shark Bay), along parts of coastal SA, in northern Tasmania, in a band from south-central Victoria to the tablelands and western slopes in southeastern NSW, and in southeast Queensland. Rainfall deficiencies at this time-scale were eased or removed in southeast Queensland as a result of above to very much above average August rainfall. Record low falls for this particular 12-month period were recorded just to the east and southeast of Melbourne, and along WAs west coast between Shark Bay and Geraldton.

Despite the rapid demise of the 2006 El Niño event, the Murray-Darling Basin (MDB) is still to see a sustained period of above average rainfall in the intervening period. This is the first time in the record dating from 1900 that an El Niño-drought in the MDB has not been followed by at least one three-month period with above normal rainfall (basin average) by the end of the following winter. Almost the entire basin shows well below average rainfall for periods starting in 2006.

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The deficiencies discussed above have occurred against a backdrop of multi-year rainfall deficits and record high temperatures that have severely stressed water supplies in the east and southwest of the country. Several years of above average rainfall are required to remove the very long-term deficits. Furthermore, the combination of heat and drought during the past five to ten years over the MDB and southeastern Australia, is outside the typical range of variability experienced during the previous 100 years.