Issued 4 October 2006

Rainfall deficiencies intensify in SA, NSW & Vic, but ease in WA

September 2006 saw continued below average rainfall across southern and central parts of the mainland, with deficiencies generally expanding or intensifying over South Australia, New South Wales and Victoria. Furthermore, the dryness was exacerbated by temperatures that were well above normal. In contrast, deficiencies eased in WA as a result of very much above average September rain. Near-average totals over much of Tasmania were welcome, but had only a small impact on deficiencies for various periods extending back to the start of the year.

4-month rainfall deficiencies

For the 4-month period from June to September, generally severe rainfall deficiencies covered most of the area south of a line from Exmouth (WA) to Eucla (WA) to Tarcoola (SA) to Mildura (Vic) to Albury (NSW) to Canberra (ACT) to Sale (Vic), as well as northern, central and eastern Tasmania. Record low totals occurred in scattered patches over WA (these were much less extensive than those at the end of August), in parts of southern Victoria and in a few patches across Tasmania. Multi-year rainfall deficits in the southeast have been exacerbated by the most recent period of suppressed rainfall.

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7-month rainfall deficiencies

For the 7-month period from March to September, serious to severe rainfall deficiencies extend in a band from southeast SA to central Victoria to the central-west of NSW. Record low falls have occurred in a band extending southwest from Orange (NSW) to the far northeast of Victoria. An area to the east of Melbourne and another region on the SA/Vic border have also had their driest March-September on record. The zone from north of Carnarvon to Albany in western WA is also affected, with patches of lowest on record falls along the coast (less extensive than at the end of August).

There were only minor changes to the patterns of deficits over Tasmania and southeast Queensland for this period.

Rainfall deficiency maps for longer periods indicate that deficiencies at the three year time-scale, which are particularly relevant to water supplies, remain prevalent in parts of eastern Australia, especially in Queensland.

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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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