Issued on 6 June 2011

Dry conditions continue in southwest WA

Rainfall across Australia was below average during May 2011, the first below average month since June 2010, the start of the 2010-2011 La Niņa event. The largest areas of below average rainfall were in the north of the country. Much of Tasmania, northern and western parts of Victoria and southwest WA were also dryer than usual.

17-month rainfall deficiencies

For the 17-month period from January 2010 to May 2011, rainfall deficiencies remained in place through much of southwestern WA. Despite some rain at the end of the month, below average total rainfall during May 2011 over much of the southwest region reinforced deficiencies. Areas of rainfall deficiency are very similar to those reported in the previous drought statement, with a large area of lowest on record rainfall covering much of the southwest corner, and severe deficiencies over most areas southwest of a Geraldton-Esperance line, except near the south coast from Albany eastwards. To relieve most areas in southwest WA, i.e. just to get out of the "serious deficiency" (or lowest 10%) category, rainfall for the next three months will have to be in the "above average" category. For parts of the Lower West, Southwest, southern Central Wheat Belt and northern Great Southern, the coming three months rainfall would have to be in the "very much above average" category, i.e. the highest 10% of such periods on record.

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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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