Issued 3 October 2008

Long and short-term rainfall deficiencies persist

Below average September 2008 rainfall over Victoria, southern NSW, SA and the WA interior maintained short and long-term deficiencies in these areas. In contrast, average to above average September falls over much of the remainder of the country gave some minor relief to short-term deficits over southwest WA, northeast NSW, southwest NT and Queensland. It should be noted that only a small amount of rainfall was needed to reduce deficits over southwest NT, as rainfall is climatologically low at this time of the year for this area.

7-month rainfall deficiencies

For the 7-month period from March 2008 to September 2008, areas of serious to severe rainfall deficiencies have persisted over parts of western Queensland, the NT, southern NSW, central and eastern Victoria, eastern Tasmania, the SA pastoral districts and most of the WA interior. Above average September rainfall over northern NSW, most of Queensland, Tasmania, the NT and southwest WA contributed to a reduction in the area of land affected by short-term rainfall deficiencies in these regions. In particular, severe deficiencies observed in the 6 months ending 31 August 2008 over northeast NSW and southeast Queensland have eased significantly.

In contrast, below average September rainfall across SA, the interior of WA, Victoria and southern NSW maintained short-term deficiencies, with some intensification of deficiencies observed in SA. In northern Australia, short-term deficiencies are generally a result of a poor end to the 2007/2008 wet season, whereas, in southern Australia a drier than normal 2008 wet season has been the main contributor to deficiencies. Lowest on record September rainfall over parts of Victoria, southern NSW, SA and the WA interior has placed severe stress on farming activities in these regions.

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16-month rainfall deficiencies

Rainfall deficiencies for the 16-month period from June 2007 to September 2008 persist over much of SA, 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. The largest area of lowest on record rainfall for the period is in eastern Tasmania, north of Hobart, with only a couple of small isolated record dry areas elsewhere. The anomalies are remarkable given that they partly coincide with a La Niña event. La Niña events are usually associated with above average rainfall rather than widespread rainfall deficiencies. Although some parts of the country 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.

There were only marginal changes in the areas of long-term deficiencies in September, with a small reduction in area of severe deficiency over the southwest WA coastal district, but a slight increase in area of the serious deficiency over the WA interior. The area of severe deficiency over SA and Victoria has slightly increased in size, with a few more isolated lowest on record areas now evident in SA. Deficiencies also slightly eased in Tasmania, due to above average September rainfall in the region. The areas of long-term deficiencies generally highlight areas that failed to receive good falls during the 2007 La Niña event, with large areas of deficiencies through central and southern parts of the country.

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.

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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