Issued 7 January 2008

Short-term deficiencies ease, long-term deficiencies remain

An established La Niña event contributed to above average December rainfall across much of the country, especially in the east, which eased short-term rainfall deficiencies in many areas. Whilst some deficiencies still remain, especially in South Australia and Western Australia, these are not as extensive or severe as they were at the end of November. Short-term deficiencies have eased in eastern Australia, excluding Tasmania, but long-term deficiencies remain, especially in Tasmania, southeast Queensland, the southwest coast of WA and central Victoria into southern NSW.
See December rainfall pattern

7-month rainfall deficiencies

For the 7-month period from June to December 2007 areas of serious to severe rainfall deficiencies covered parts of central and northeast SA, together with a small area in the southern NT, scattered parts of WA, western NSW and an area in eastern Tasmania. However, when compared to the end of November, the total area of severe deficiencies and lowest on record falls has greatly decreased, especially in SA, with only central SA showing small areas of lowest on record. Above to very much above average December rainfall also resulted in the easing or removal of deficits across large parts of western Victoria, WA and southwestern NSW in comparison with the situation at the end of November.

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24-month rainfall deficiencies

Rainfall deficiencies for the 24-month period from January 2006 to December 2007 were widespread across the southeastern corner and southwestern coastal parts of the continent. Southeastern Queensland and northcentral and southeastern SA were also affected. There were areas of lowest on record in WA from north of Perth to Carnarvon and in a large band from the east of Melbourne to the south of Canberra.

The worst of the long-term deficiencies are likely to remain for some time, for example, above average (decile 8-9) rainfall is needed in the rainfall deficient areas over the next twelve months to elevate totals since January 2006 out of the lowest decile.

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 Murray Darling Basin and southeastern Australia is outside the typical range of variability experienced during the previous 100 years. For more information go to a recent Special Climate Statement on the six years of widespread drought in southern and eastern Australia, November 2001 to October 2007

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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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