Issued 8 April 2016
March rainfall reduces deficiencies in some areas
Rainfall in March was above average to well above average in the southwest of Western Australia. Much of South Australia recorded well above average rainfall with areas of highest on record in parts of the Western Agricultural district. Consequently rainfall deficiencies reported in the southwest of Western Australia in the previous drought statement have contracted toward the western coast and reduced in severity. Similarly deficiencies in South Australia have been removed from all areas over all time scales with the exception of the far southeast and some coastal regions.
Above average rainfall was recorded in parts of northern and western Queensland, giving a significant reduction in shorter-term deficiencies near the coast, but long-term deficiencies in the interior of Queensland only weakened and contracted marginally. Southern parts of the Northern Territory observed above average rainfall but this has had little impact on the deficiencies in the north of the Territory. In the northwest of the country, the Pilbara and far northern coastal parts of the Western Australia and the Top End received less than average rainfall during March and as a result short term deficiencies in these areas have expanded and become more severe.
Rainfall in eastern Australia, especially in the southeast and over large parts of Queensland, has generally been very much below average for the period since the conclusion of the last La Niña in autumn 2012. The past 48 months has also been the warmest such period on record, which is likely to have added to the impact of the rainfall deficiencies. Long-term deficiencies also exist in southeastern and southwestern Australia over the 16 years since 2000, which has also been the warmest such period on record.
11-month rainfall deficiencies
The rainfall in March has somewhat reduced the deficiencies about the central coast of Queensland and has led to contraction of the affected areas around northern Cape York Peninsula. In contrast the area affected northeast of Darwin has expanded and increased in severity.
Rainfall deficiencies in South Australia's Pastoral district have been removed. Deficiencies in the southeast of the State have contracted towards the south but remain serious to severe. Serious to severe deficiencies persist in western and central Victoria and in western Tasmania.
Areas of serious to severe deficiency continue in southwest Western Australia however, they have contracted to the west significantly. In northern parts of Western Australia deficiencies persist and there has been an expansion of a serious deficiency in the eastern Pilbara.
21-month rainfall deficiencies
The rainfall in March had an impact on deficiencies over the period starting July 2014. Above average rainfall recorded in western and northern Queensland led to significant easing and contraction of deficiencies in those areas. While Queensland saw a general reduction of the extent and severity of rainfall deficiencies, they persist along the northern coast and central interior. Some areas of serious deficiency remain around the Gulf of Carpentaria. Previously serious to severe deficiencies in the Pastoral districts of South Australia have significantly contracted to the southern coast of the State. In addition, deficiencies eased about the southern coastal parts of South Australia and the Eyre Peninsula.
The area of lowest on record and significant areas of serious deficiency remain in place about the southeast of South Australia and western and central Victoria. Serious to severe deficiencies have eased over northeastern Tasmania, but remain in the west of the State and there has been a slight broadening of the serious deficiencies across southern Tasmania. There has been a substantial contraction and easing of the area affected in the southwest of Western Australia, due in part to well above average March rainfall.
42-month rainfall deficiencies
The period starting in October 2012, which now runs to 42 months, show serious to severe rainfall deficiencies have slightly eased or contracted in Queensland over the last month.
Areas of serious to severe deficiency remain through the far south of Cape York Peninsula extending southward through inland Queensland and into northern central New South Wales. Serious to severe deficiencies expanded westward over the Northern Slopes and Tablelands of New South Wales. Serious to severe deficiencies are also evident at the 42-month scale in a zone from southeastern South Australia, across the western half of Victoria, and in parts of western and southeast Tasmania.
Areas of serious deficiency have contracted but still remain in southwest Western Australia, and on the far northern coasts of the Top End and the Kimberley.
Very long term deficiencies persist
The rainfall deficiencies in southern Australia at periods up to 42 months are also evident on much longer timescales. The map of rainfall deficiencies for the past 16 years shows record low rainfall over most of southwest Western Australia, with serious to severe deficiencies widespread in northern and central Victoria, neighbouring parts of South Australia and New South Wales, and northern and western Tasmania. Patchy deficiencies are also evident in Queensland, most notably in western parts of the Darling Downs.
The affected regions typically receive significant rainfall during the period from autumn through spring from cold fronts and low pressure systems. However, Australia has experienced a substantial decrease in this activity over recent decades, as high pressure systems have become more dominant. This suggests the tendency for recurrent dry conditions is less related to variations such as El Niño, and more due to other changes in the climate system. Research suggests that long-term drying trends over southern Australia cannot be explained by natural variability alone.
These very long term deficiencies are most significant for long-term processes, though recurrent dry seasons may have direct agricultural impacts. These longer-term processes include recharge of surface and ground water storages, and the drying of forest fuels. It is noteworthy that rainfall in northern Australia has been very high during the same period, and particularly so in northwest Australia.
Soil moisture for March 2016 in the lower layer (from 10 cm to 100 cm deep) continued to be very much below average over western Tasmania, in areas of the far northwest of the country, in northern and central parts of Cape York Peninsula and in patches of the far northern Queensland coast. An area of very much below average soil moisture emerged in northeastern New South Wales. Soil moisture was below average over the western half of Tasmania, central southern Victoria, all but the far west and south of New South Wales, southern Queensland, and large areas of the northwest and north of the country.
Lower layer soil moisture was above average in the southwest of Western Australia and through much of South Australia. Well above average soil moisture exists in the southeast of Western Australia, through Pastoral districts and coastal areas of South Australia. Above average lower layer moisture is evident in southern parts of the Northern Territory, Queensland's central interior and far southwest, and in the southwest of Cape York Peninsula.
Soil moisture information presented here is from the Bureau's operational Australian Water Resources Assessment Landscape (AWRA-L) model, developed through the Water Information Research and Development Alliance between the Bureau and CSIRO. More information on the model used and the totals that the decile ranges represent can be found at the new Australian Landscape Water Balance website.
Product Code IDCKGD0AR0
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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.
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Rainfall averages, variability and trends
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%.
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Very much above average – rainfalls in the highest 10% of historical totals.