Issued on 4 May 2011

Mixed rainfall for April 2011

Rainfall across Australia was mixed during April 2011. All states and territories showed some areas of below average rainfall and some areas of above average rainfall. The largest areas of above average rainfall were in the north of the country, mainly over the Kimberley and northern parts of the NT, while the largest areas of below average rainfall occurred in the centre of the continent, with smaller areas along the southern coast and in western parts of WA.

16-month rainfall deficiencies

For the 16-month period from January 2010 to April 2011, rainfall deficiencies remained in place through much of southwestern WA; above average rainfall during April 2011 in some near-coastal areas between Perth and Albany was insufficient to have any significant impact on the situation. 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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