Issued on 6 September 2011

Winter brings no relief to long-term rainfall deficiencies in southwest WA

Rainfall across Australia was mixed during winter 2011. Much of NSW and Victoria recorded below average rainfall over winter. Averaged across the Murray Darling Basin it has been the driest winter since 2002. In contrast, very much above average rainfall was recorded in a large band across southern parts of WA from inland of Geraldton to the SA border, though missing the main areas of rainfall deficiencies.

20-month rainfall deficiencies

For the 20-month period from January 2010 to August 2011, rainfall deficiencies remain in place through much of southwestern WA. Much of the region experienced average to below average rainfall over winter. This has maintained areas of long-term rainfall deficiency which 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.

Parts of northern inland NSW, which missed the heaviest of the summer rains, have had below-average rainfall since January, with localised 8-month rainfall deficiencies emerging along a narrow strip extending from Mudgee to Walgett. Furthermore, after the very wet March, rainfall in inland parts of southeastern Australia has also 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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