Issued 5 November 2008

Rainfall deficiencies expand in southeastern Australia

Below average October 2008 rainfall over Victoria, Tasmania, SA, southern and western NSW, southeastern Queensland and the WA interior maintained, and in some cases increased, short and long-term deficiencies in these areas. This was particularly evident in the short-term in parts of eastern Tasmania and Victoria, with areas of lowest on record totals increasing.

8-month rainfall deficiencies

For the 8-month period from March to October 2008, areas of serious to severe rainfall deficiencies have persisted over much of Victoria (extending into southern NSW and the far southeast of SA), eastern Tasmania and central and western SA extending into the WA interior. Below average October rainfall over central and southeastern Australia resulted in a maintenance or increase of deficiencies in these areas. In particular, serious and severe deficiencies have expanded over southwestern Victoria and SA. Areas of lowest on record expanded in the far east of Victoria and adjoining south-eastern NSW between Orbost and Bombala and on the east coast of Tasmania between Hobart and St. Helens. Significant areas of lowest-on-record rainfall have developed in central Gippsland around Sale. The record dry start to spring across SA, and the third driest start to spring in Victoria, has contributed to the expansion of areas of rainfall deficiencies across these states in recent months. The timing of these below average falls has placed severe stress on farming activities in these regions.

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17-month rainfall deficiencies

Rainfall deficiencies for the 17-month period from June 2007 to October 2008 persisted over much of SA, southern NT and also in parts of southern WA, far western parts of both Queensland and NSW, western and central Victoria and northern and eastern Tasmania. The largest area of lowest on record rainfall for the period is in eastern Tasmania, with some small isolated areas of lowest on record falls evident elsewhere, especially in SA. The anomalies are all the more remarkable given that they partly coincide with a La Niña event. La Niña events are usually associated with above average rainfall across much of the eastern half of Australia rather than widespread rainfall deficiencies. The areas of long-term deficiencies generally highlight areas that failed to receive good falls during the 2007/08 La Niña event, with large areas of deficiencies through central and southern parts of the country. Although some regions, especially in the northeast, saw above average rainfall between November 2007 and February 2008, months of below average rainfall before and after this period have dominated long-term anomalies, especially in southeastern and central parts of Australia.

There were only small changes in the areas of long-term deficiencies in October, with some increase in the area of serious and severe deficiency over SA and Victoria. The area of lowest on record totals increased in number in SA and expanded in eastern Tasmania.

The deficiencies discussed above have occurred against a backdrop of decade-long rainfall deficits and record high temperatures that have severely stressed water supplies in the east and southwest of the country. The combination of record heat and widespread drought during the past five to ten years over large parts of southern and eastern Australia is without historical precedent and is, at least partly, a result of climate change.

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Definitions

Lowest on record - lowest in the historical analysis, which runs from 1900.
Severe deficiency - rainfalls in the lowest 5% of historical totals.
Serious deficiency - rainfalls in the lowest 10% of historical totals, but not in the lowest 5%.

Very much below average - rainfalls in the lowest 10% of historical totals.
Below average - rainfalls in the lowest 30% of historical totals, but not in the lowest 10%.
Average - rainfalls in the middle 40% of historical totals.
Above average - rainfalls in the highest 30% of historical totals, but not in the highest 10%.
Very much above average - rainfalls in the highest 10% of historical totals.

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