Issued on 6 November 2014
Rainfall deficiencies worsen in southeast Australia
October was a dry month with below-average to very-much-below-average rainfall affecting most of Australia with the notable exception of inland Western Australia. Nationally, it was the seventh-driest October on record (with area-averaged rainfall 59% below mean). It was especially dry across South Australia, which recorded its driest October on record with low totals affecting adjacent parts of Victoria and New South Wales. Recent below-average rainfall across southern Australia has contributed to widespread rainfall deficiencies in the second half of the southern growing season (July to October). Rainfall deficiencies have persisted at both longer (25-month) and shorter (11-month) timescales.
4-month rainfall deficiencies
Below-average October rainfall across much of eastern Australia has increased the area of serious and severe rainfall deficiencies in southern New South Wales, western and northern Victoria and much of southern South Australia. Areas of short-term rainfall deficiencies are also present in western Queensland and the Northern Territory, although this is typically a dry time of year for the region. Smaller areas of short-term deficiencies are also present between Carnarvon and Exmouth in Western Australia and from southeast Queensland across the border into New South Wales.
11-month rainfall deficiencies
Below-average October rainfall has increased the extent and severity of deficiencies for the 11-month period over much of southeast Queensland and northeastern New South Wales. Further south, a very dry month for western Victoria and southeastern South Australia has led to an increase in deficiencies in the region, with small areas of severe deficiency (lowest 5% of records) emerging. Serious and severe deficiencies in eastern Tasmania have also worsened.
25-month rainfall deficiencies
At the longer 25-month (October 2012 to October 2014) timescale, rainfall deficiencies persist across central to western Queensland and inland northeastern New South Wales. Rainfall deficiencies have again increased in spatial extent and severity in inland western Victoria.
Serious and severe deficiencies (lowest 10% and 5% of records) remain in an area spanning much of Queensland away from the eastern coast and also in smaller areas in adjacent parts of the Northern Territory and South Australia, and in an area inland of the Great Dividing Range extending from southern Queensland into northern New South Wales. Deficiencies are also present across much of inland western Victoria, extending across the border into part of southeastern South Australia, and in an area of the southern coastal Gascoyne around Shark Bay in Western Australia.
The deficiencies in Queensland at this 25-month period are largely the result of below-average rainfall over two wet seasons. Over the coming six months, rainfall will have to be average to above average over much of this area to lift the total rainfall out of deficiency, i.e. above the tenth percentile.
Upper layer weekly soil moisture for the week ending 2 November was very much below average across the majority of Australia excluding the west and south of Western Australia and Tasmania, where soil moisture was generally above average. The broad area of elevated soil moisture in Western Australia and western Tasmania is a result of recent rainfall. Small areas of above-average soil moisture are also evident at the weekly scale in far eastern Victoria and West Gippsland.
Compared to last month, lower layer weekly soil moisture for the week ending 2 November has increased in an arc across much of northern Australia, the inland west and coastal South Australia through to Tasmania. Soil moisture has decreased across southeastern Queensland and northeastern New South Wales. Soil moisture is below average across parts of inland central and southeastern Queensland, northeastern New South Wales extending inland of the Great Dividing Range into western Victoria, in parts of eastern Tasmania, along the west coast of Western Australia extending from the Pilbara to the Central Wheat Belt and in the central Top End. Soil moisture is above average across the central Cape York Peninsula, central Northern Territory and much of the western half of Western Australia as well as pockets of the coastal Top End. Soil moisture is also above average in southwest Western Australia, across the Nullarbor Plain and much of southern South Australia and also in northern Tasmania and an area of far eastern Victoria.
Product Code IDCKGD0AR0
The Weekly Rainfall Update describes rainfall over the previous week. It includes a map and a summary table of the highest weekly totals. A discussion of the impact of recent rains on rainfall deficiencies is also presented.
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Drought is a prolonged, abnormally dry period when the amount of available water is insufficient to meet our normal use. Drought is not simply low rainfall; if it was, much of inland Australia would be in almost perpetual drought. Because people use water in so many different ways, there is no universal definition of drought. Meteorologists monitor the extent and severity of drought in terms of rainfall deficiencies. Agriculturalists rate the impact on primary industries, hydrologists compare ground water levels, and sociologists define it by social expectations and perceptions.
Rainfall averages, variability and trends
Lowest on record - lowest since at least 1900 when the data analysed begin.
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.