Drought Statement - Issued 6th May 2009

For the 23-month period ending 30th April 2009
Issued on 6th May 2009 by the National Climate Centre

Long-term rainfall deficiencies persist over southeastern Australia

Rainfall deficiencies definition
23-month rainfall deficiencies

A dry start to the year across southeastern Australia has been followed by generally average to above average rainfall in March and April. In contrast, a wet start to the year across northern Australia has been followed by generally below to very much below average March and April rainfall in many areas, and there has been a dry start to the rainfall season in the south-west of Western Australia.

Significant areas of rainfall deficiencies are evident when periods greater than 12 months are considered, but vary in location and intensity depending on the period selected. The 23-month period has been chosen for this statement as it shows some of the largest areal extent of deficits across the country. The period starting in January 2008, which has been included in recent statements, is no longer being reported on as the areas affected by deficits at the 16- and 23-month timescale are very similar. Some parts of the country are also affected by longer-term deficiencies, extending out to several years.

For drought periods of 4 months or less short-term deficiencies are evident over parts of Victoria, due to the dry start to 2009 mentioned above, and for the 3-month period deficiencies have emerged in parts of central Australia. Drought periods greater than 4 months and less than 12 months generally show only small and isolated areas of rainfall totals in the lowest 10% of historical records.

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

For the 23-month period from June 2007 to April 2009, serious to severe rainfall deficiencies are evident across much of southeast Australia and parts of central Australia. These deficiencies cover most of the agricultural areas of SA, central and western Victoria, eastern and northern Tasmania and some southern border areas of NSW. A small area of lowest of record is evident in the Wimmera district of Victoria. Although deficits for periods of three or more years linger in parts of southeast Queensland and northeast NSW, for the 23-month period to April 2009 these areas benefited from above average rainfall associated with the 2007/08 La Niña. However, in southeastern and central Australia, apart from wet November-December periods in both 2007 and 2008, rainfall was generally below to very much below average.

The Indian Ocean Dipole (IOD) is a pattern of sea surface variability across the Indian Ocean that is associated with lower than normal rainfall over central and southern Australia when it is in a positive phase (see IOD). Both 2007 and 2008 were consecutive years of sustained positive IOD, which partly explains rainfall deficits through the 23-month period in these areas. The IOD usually has its greatest impacts between June and November.

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 twelve 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 recent Special Climate Statement on the long-term drought in southern Australia 'Long-term rainfall deficiencies continue in southern Australia while wet conditions dominate the north', issued 10 October 2008. Despite the generally wet conditions in November and December, dry conditions in October and since the start of 2009 have resulted in these long-term deficiencies remaining fairly stable over the last few months.

More information on the climate of Australia during 2008 can be obtained from the Annual Australian Climate Statement.

Note: The terms used to describe rainfall in these Drought Statements have the following meanings -

Serious deficiency - rainfalls in the lowest 10% of historical totals, but not in the lowest 5%
Severe deficiency - rainfalls in the lowest 5% of historical totals
Lowest on record - lowest since at least 1900 when the data analysed begin

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

For more information regarding this rainfall deficiencies statement, please contact the following climate meteorologists in the National Climate Centre:

Blair Trewin on (03) 9669 4623
Grant Beard on (03) 9669 4527
Andrew Watkins on (03) 9669 4360

External Sites Relating to Drought

The Bureau of Meteorology does not make formal drought declarations as these are done by either the relevant State Governments or by the Australian Government. The Australian Government Program is called Exceptional Circumstances and it is administered by the Federal Department of Agriculture, Fisheries and Forestry (DAFF). General information about Australian Government drought assistance is available at http://www.daff.gov.au/droughtassist.

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