Issued on 7 September 2009

Short-term deficits worsen over the south coast of NSW and over central and eastern Victoria

August 2009 was generally a dry month over mainland Australia, particularly over NSW and Queensland. Conversely, it was a very wet month over Tasmania. More information about Australia’s rainfall in August is available here.

8-month rainfall deficiencies

For the 8-month period from January to August 2009, serious to severe rainfall deficiencies remain evident over the south coast of NSW and over central and eastern Victoria. A few very isolated areas of serious to severe deficiencies also remain evident across central Australia and in parts of southwest WA, including an area of the Great Southern district centered on Lake Grace. Several stations near Melbourne and in Gippsland have recorded lowest on record rainfall for the period. Low August rainfall across all of these regions has resulted in a slight worsening of the short-term deficits compared with those that existed for the 7-month period ending July 2009.

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24-month rainfall deficiencies

For the 24-month period from September 2007 to August 2009, serious to severe rainfall deficiencies remain evident across large areas of mainland southeastern Australia (mainly in Victoria) and parts of central Australia. Given that August 2009 was much wetter than August 2007 in Tasmania, 24-month deficits that were apparent in that state at the end of July 2009 had almost disappeared by the end of August.

The regions affected by deficits experienced some average to above average rainfall during the final months of both 2007 and 2008, as well as during autumn and winter this year. However, most months through the period were drier than the long-term mean, especially during the growing seasons of 2007 and 2008. Both 2007 and 2008 were classified as positive Indian Ocean Dipole (IOD) years, which is likely to have partly contributed to the low winter and spring rainfall recorded across parts of southern Australia during both these years.

Rainfall deficiency maps for standard periods out to three years are available here.

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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