Issued on 6 October 2014 by the National Climate Centre
Rainfall deficiencies worsen in Victoria and Tasmania
September rainfall was below to very much below average across most of southeastern Australia, especially in western Victoria, southeastern South Australia and parts of Tasmania. Below average rainfall across southern Australia, especially in August and September, has contributed to widespread rainfall deficiencies across southeastern Australia in the second half of the southern growing season to date (July - September). Rainfall deficiencies have increased in severity and extent at long (24-month) timescales in western Victoria and for shorter (10-month) timescales near Tasmania's East Coast.
September rainfall was also below average for much of central and northern Australia, although September is typically a dry-season month in those regions. Above-average rainfall along the western and southern coast of Western Australia brought some relief from deficiencies, especially at the shorter timescale, with above-average rainfall in central eastern Queensland also easing deficiencies somewhat in that region.
10-month rainfall deficiencies
Above-average September rainfall has significantly eased deficiencies for the 10-month period along the western coast of Western Australia and in eastern Queensland north of Bundaberg. In contrast, much of southeast Queensland and eastern New South Wales received below-average monthly totals leading to a slight increase in deficiencies. Further south, a very dry month for western Victoria and eastern Tasmania, with monthly totals in the lowest 10% of records, saw deficiencies expand to cover much of inland western Victoria from Port Phillip Bay to just across the South Australian border, in pockets of Tasmania's west coast, and in eastern Tasmania, with Tasmania's lower East Coast in the lowest 5% of records. Serious and severe deficiencies (lowest 10% and 5% of records) are also present in a large area of northeastern New South Wales and southeastern Queensland and small areas of the southern coast of Western Australia.
Much of western Victoria, southeastern South Australia and southern New South Wales are also experiencing serious or severe deficiencies at short timescales such as the 3 months to September 2014 as a result of particularly poor late winter/early spring rainfall in 2014.
24-month rainfall deficiencies
At the longer 24-month (October 2012 to September 2014) timescale, rainfall deficiencies have been reduced by September rainfall on the west coast near Shark Bay and decreased slightly in part of inland eastern Queensland although generally remaining similar across most parts of Queensland when compared to the 23-month period ending September. 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.
More generally, rainfall for the 24-month period ending September 2014 has continued to be below average over the eastern mainland and Tasmania and along the west coast of Western Australia. There are large areas of Australia which have seen rainfall which is below-average but above the lowest 10% of records, highlighting that the spatial extent of below-average rainfall in the coastal west and eastern Australia is widespread on this timescale.
Longer-term multi-year deficiencies (greater than two years) stretch back to the termination of the 2011–12 La Niña are evident across scattered parts of eastern Australia and parts of the far southwest. These currently cover more than 40% of Victoria, 30% of Queensland and nearly 20% of New South Wales. These longer-term deficiencies will be described in more detail at the end of October which marks the last month of the winter rainfall 'season'.
Upper layer weekly soil moisture for the week ending 28 September was below to very much below average across much of Victoria and the mainland south coast, Tasmania, the Northern Territory and central Australia. Soil moisture was above average in Western Australia from the western coast through to the Eucla District, in northwestern New South Wales and adjacent South Australia and in a large area of central eastern Queensland. The broad area of elevated soil moisture in eastern Queensland is a result of recent rainfall, as is the region in Western Australia.
Lower layer weekly soil moisture for the week ending 28 September remains similar to last month apart from extensive drying seen across Victoria, and to a lesser extent, Tasmania. Soil moisture was below average across parts of inland 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 along the south coast from the Nullarbor Plain through to eastern South Australia and in 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.