Issued 6 August 2008

Rainfall deficiencies persist over much of Australia

Near-normal rainfall in July 2008 over large parts of southern Australia, along with unseasonable winter rains in eastern tropical and subtropical Queensland, brought some relief to short-term rainfall deficiencies. However, these rains made little impact on longer-term deficiencies at the 14-month timescale. These highlight areas that received little rainfall relief from the previous year's La Niña event, with large areas of deficiencies through central and southern parts of Australia.

5-month rainfall deficiencies

For the 5-month period from March 2008 to July 2008, areas of serious to severe rainfall deficiencies covered much of the southern interior of WA and adjoining areas of north-western SA and the south-western NT; far western Queensland and the Barkly region of the NT; eastern Tasmania; and southern Victoria from Geelong eastwards, extending into the far south-east of NSW. There were also isolated areas of serious to severe rainfall deficiencies scattered through inland NSW, especially the south, and southern inland Queensland. In northern Australia this was indicative of an early end to the wet season, whilst southern Australia has generally experienced a poor start to the southern wet season. Unseasonable winter rains, with widespread falls of 50 to 200 millimetres in the second half of July, have removed short-term rainfall deficiencies through most of eastern Queensland, whilst near-normal July rains have eased the situation in Victoria, especially in the north and west, and good July rains have also eased or removed rainfall deficiencies around Esperance and Norseman in WA.

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14-month rainfall deficiencies

Rainfall deficiencies for the 14-month period from June 2007 to July 2008 remain evident over much of SA, including most of the agricultural districts, and the 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. Over the 14-month period, much of eastern Australia had some benefit from above average rainfall associated with the 2007/08 La Niña event. However, this was mainly over late 2007 to around February 2008, with typically below average rainfall since. Although Victoria received average to above average falls over summer, the combination of very much below average rainfall since the start of autumn and a dry winter in 2007, has resulted in central and western parts of the state being in decile 1 for the 14-month period. Tasmania, central areas of Australia and some southern parts of WA, which did not receive as much relief from the La Niña event, have also seen typically below average falls in recent months, leading to a continuation of rainfall deficiencies over the 14-month period. Patches of lowest on record rainfall for the period are seen in eastern Tasmania north of Hobart, around Tarcoola and Leigh Creek in SA, and the NT to the east of Alice Springs, extending into the far west of Queensland. There were only marginal changes in the areas of longer-term deficiencies in July, although average to above average rains on the Eyre Peninsula in SA lifted 14-month rainfalls above the lowest-on-record levels at which they had been over the period ending in June.

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. Several years of above average rainfall are required to remove the very long-term deficits. 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. For more information go to a 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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