Issued 3 August 2007
Most states still affected by rainfall deficiencies
At the yearly time-scale, rainfall deficiencies are evident in all states and territories, with the exception of the Northern Territory. As July 2007 was wetter than July 2006 in western WA, Victoria and southeast SA, there was a slight easing of 12-month deficits in those regions compared with the situation at the end of June. However, southeast Queensland, Tasmania and the Eyre Peninsula experienced a drier July this year thereby causing 12-month rainfall deficiencies to expand and intensify.
12-month rainfall deficiencies
For the 12-month period from August 2006 to July 2007, there were serious to severe rainfall deficiencies over southern and eastern Australia in an arc extending across the Eyre Peninsula and southeastern SA, southwest, south-central and northeast Victoria, and the tablelands and western slopes in southeastern NSW. A large part of southeast Queensland was also affected, as were Tasmania (except for the southwest), and parts of western WA between Carnarvon and Perth as well as areas between Wagin and Albany.
Record low falls for this particular 12-month period were recorded southeast of Melbourne, in much of northern and central Tasmania, in the far southeast of SA and along WA’s west coast between Shark Bay and districts to the south of Geraldton.
Over the past three months (May to July), rainfall deficiencies have developed in southwest WA between Geraldton and Kalgoorlie and between Kalgoorlie and Esperance, these being areas largely unaffected by 12-month deficiencies.
The worst of the long-term deficiencies are likely to remain for some time. For them to be removed by the end of October, for example, falls over the next three months would need to be in the highest 10% of the historical record in some areas, especially near Melbourne, in northern Tasmania, western WA and southeast Queensland.
The deficiencies discussed above have occurred against a backdrop of multi-year rainfall deficits that have severely stressed water supplies in the east and southwest of the country.
An important consideration in the recovery from drought is the different rate at which systems respond to rainfall deficiencies. At the current time, many catchments in eastern Australia are excessively dry from a very protracted period of below average rainfall and above average temperatures. This means that it will take above average rainfall just to produce average runoff, and very considerable rainfall to make a material difference to water storages.
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.
Product Code IDCKGD0AR0