Issued on 3 August 2011

Long-term rainfall deficiencies persist in southwest WA

Rainfall across Australia was mixed during July 2011. The largest areas of below average rainfall were in inland NSW and northwestern Victoria, leading to a continuation of short term dry conditions in these areas. Much of central WA and northern and western parts of SA experienced above average rainfall.

19-month rainfall deficiencies

For the 19-month period from January 2010 to July 2011, rainfall deficiencies remain in place through much of southwestern WA. Although much of southwestern WA recorded rainfall totals above 50mm for the month, this was typically average to below average for July. Areas of long-term rainfall deficiency remain 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.

After the very wet March, rainfall in inland parts of southeastern Australia has been below average. This continues a trend in recent decades of unusually dry mid-autumn to early-winter conditions to recur in most years (for example Victoria has experienced below average April-July rainfall in 10 of the last 11 years). This is a topic of active research, and climate scientists will be closely monitoring rainfall in this region.

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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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