Issued 4 April 2005

Rainfall deficiencies expand in northwestern and central Australia

The Bureau of Meteorology announced today that the total area of rainfall deficiencies has expanded, and now extends across the continent in a band from Port Hedland/Broome in the northwest of WA, to Bourke in northwestern NSW. This broad region of deficiencies is largely the result of very low wet season rainfall for much of the northern half of the continent. This has been due to both the sporadic nature of the northern monsoon during the 2004-05 wet season, as well as its failure to penetrate far southward. March rainfall totals saw a continuation of this pattern, with much of northern Australia receiving only 20% or less of their mean monthly rainfall, however some areas in the far northwest did receive above average falls for the month and hence serious deficiencies have been erased in some areas.

The impact of the low rainfall totals in northern Australia has been further affected by very high temperatures for the wet season so far. For October to March, the mean temperature for northern Australia has been +0.9°C above normal, 0.1°C warmer than the previous hottest wet season in 1997-98. Likewise maximum temperatures have been nearly 1.3°C above normal for the same period, 0.3°C above the previous record for northern Australia set in 1979-80.

9-month rainfall deficiencies

For the 9-month period from July to March, a large area of severe rainfall deficiencies extends from far western WA and western central NT to just north of Marree in SA. This area includes some regions of lowest on record rainfall, notably near Alice Springs, Giles and west of Tenant Creek. Other areas of severe deficiency exist between Dampier and Broome (WA), north of Bourke (NSW) and west of Charleville (QLD) as well as localised pockets in northeastern Tasmania and southwestern WA (though early April rains in southwest WA should remove most deficienies). Lowest on record falls extend inland from Port Hedland.

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Large regions in southern and eastern Australia continue to experience deficiencies for periods longer than two years indicating that there is still to be a full recovery from the very dry conditions experienced during the 2002-03 El Niño event.

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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