Issued on 3 June 2010

Dry start to the year for western WA and southern Tasmania

Below average falls over much of the western half of WA since January 2010 has contributed to a continuation of serious to severe deficiencies over this area. Across the rest of the country, except for southern Tasmania and northeastern NSW, rainfall has been generally above average. For the Murray-Darling Basin (MDB) averaged as a whole, it has been the sixth wettest start to the year since records began in 1900, while Queensland has had its wettest start to the year since 1974. It was the first autumn with above average rainfall since 2000 in Victoria and the MDB. While recent rainfall has cleared a number of short-term rainfall deficiencies across eastern Australia, serious deficiencies remain on time-scales longer than two years and continue to affect water supplies; to alleviate these would require above average rainfall for a sustained period.

5-month rainfall deficiencies

For the 5-month period from January to May 2010 serious to severe deficiencies are evident over the Pilbara and Gascoyne regions in WA, and in a large area in the Central Wheat Belt district. The southwest region also shows an area of serious to severe deficiency. Elsewhere, there is a region of serious deficiency in southern Tasmania.

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14-month rainfall deficiencies

For the 14-month period from April 2009 to May 2010, below average falls over the western half of WA during May 2010 exacerbated areas of rainfall deficiency as described in the previous drought statement, with areas of lowest on record becoming more extensive in the southern Pilbara and northern Gascoyne regions. However, above average falls in the southern coastal region around Ravensthorpe and Esperance during May have cleared the deficiencies in this area. Serious to severe rainfall deficiencies remain evident over much of the central WA coast reaching inland, covering much of the Pilbara and Gascoyne districts, where they have further intensified to some extent. Serious rainfall deficiencies also remain evident over eastern parts of the Great Southern district.

Whilst recent rains in eastern Australia have provided, in many cases, short-term relief, sustained periods of above-average rainfall are needed to remove these very long-term deficiencies. This is especially true for the very long-term deficiency periods of 8 and 13 years (see the drought statement archive). Rainfall has been below average across much of southwest and southeast Australia since 1997, whilst central and southern parts of the MDB have experienced below average rainfall since 2002. These long-term deficiencies have taken place against a background of well above average temperatures including Australia's warmest decade on record. Further information on exceptional rainfall and temperature events across Australia can be found in the Special Climate Statements.

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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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