Issued on 3 December 2009

Poor start to the northern wet season; longer-term deficits remain in parts of SE Australia

Following a generally dry October, rainfall was below average across large parts of the Northern Territory and eastern Queensland in November 2009; a poor start to the northern wet season is common during El Niño years. Short-term rainfall deficiencies expanded as a result, especially in the NT. In contrast, above average November falls in south-central Victoria eased rainfall deficits dating from the beginning of the year.

5-month rainfall deficiencies

For the 5-month period from July to November 2009, serious to severe rainfall deficiencies are evident over large areas of the NT (especially the west), spreading into adjacent parts of eastern WA. Below to very much below average rainfall in November caused these deficiencies to expand and intensify in comparison to those which existed at the end of October. There are also scattered patches of rainfall deficits for this period in central NSW, over far north Queensland, while a more coherent region covers much of southeast Queensland.

In contrast, above to very much above average rainfall during November eased or removed pre-existing deficits in the western border regions of both Queensland and NSW, including the northeast of SA.

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11-month rainfall deficiencies

For the 11-month period from January to November 2009, serious to severe rainfall deficiencies remain evident in a narrow band extending along the coast from southern NSW through Gippsland to south-central Victoria. Above normal November rainfall eased the deficits near Melbourne and in south Gippsland. However, a dry November saw deficits expand over the southern NT. The small patch of deficits near the Arnhem Land coast reflects both a poor end to the 2008-09 wet season as well poor start to the current wet season. There are also some relatively small deficit patches in southeast Queensland.

In contrast, a large region of deficits that had existed over the SA, Queensland and NSW tri-state border region was largely removed or eased by heavy November rains.

Very long-term rainfall deficiencies outside of the drought periods discussed above persist across parts of southern and eastern Australia. Most notably, rainfall has been below average across much of southwest and southeast Australia since 1997, while the Murray-Darling Basin has experienced below average rainfall since 2002.

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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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