Issued 8 March 2016
February rainfall has some effect on rainfall deficiencies
Rainfall in February was well above average along the South Australian coast and in small pockets of central Queensland. Above average rainfall was also recorded in small parts of western Victoria. Consequently, rainfall deficiencies along the South Australian coast have contracted and significantly reduced in severity over all time scales. In central Queensland the February rainfall has led to some contraction in rainfall deficiencies however the severity in this region remains largely unchanged over all time scales.
February rainfall across northern Australia was well below average. The lack of rainfall recorded in these regions saw deficiencies at various timescales, as reported in the previous Drought Statement, continue in several areas: worsening in Cape York, the Top End and parts of the Kimberley. Rainfall was also below average in the northwest of Victoria, allowing existing deficiencies at shorter time scales to extend over this area. Rain was well below average over much of New South Wales during February, although this was balanced somewhat by above-average rain in January.
Rainfall in eastern Australia, especially in the southeast and over large parts of Queensland, has been very much below average for the period since the conclusion of the last La Niña in autumn 2012. The past three and a half years have 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.
10-month rainfall deficiencies
February's rainfall has resulted in the removal of deficiencies in the Yorke and Lower Eyre Peninsulas, Kangaroo Island, and a small area in the southeast of South Australia in the period starting in May 2015. In central Queensland, rainfall deficiencies have both contracted in extent and decreased in severity, while deficiencies in southwest Western Australia remain largely unchanged.
Rainfall deficiencies in the Riverland and Murraylands districts in southeastern South Australia and parts of western and central Victoria have increased in both severity and extent. Serious to severe deficiencies have remained near the tip of Cape York and northeast of Darwin, and emerged in parts of the Kimberley in Western Australia.
Although evident at the 10-month timescale, deficiencies in South Australia, Victoria and Tasmania are particularly marked for periods starting around August or September 2015.
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20-month rainfall deficiencies
February's well below average rainfall across the tropical north impacted on deficiencies in the period starting July 2014, resulting in an increase in severity and extent in deficiencies in the Cape York Peninsula, the north tropical coast and adjacent interior, parts of the Gulf Country and the Top End. Southwest Western Australia remains in serious and severe deficiencies, although the area has contracted further west since the previous Drought Statement.
The areas of severe and serious deficiencies have contracted somewhat in the Pastoral districts in South Australia, while there has been an easing in deficiencies in the Eyre and Yorke Peninsulas, Kangaroo Island and parts of the southeast of South Australia. The area of lowest on record has reduced slightly in southwest Victoria and in southeast South Australia; however, areas of lowest on record remain largely unchanged in western Tasmania. While the severity of the deficiencies in central and western Victoria has eased, the extent of the deficiencies have expanded almost to the New South Wales border. Deficiencies remain largely unchanged in Tasmania.
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41-month rainfall deficiencies
The period starting in October 2012, which now runs to 41 months, the impact of continued low rainfall is most notable in Tasmania where serious deficiencies are now apparent in the northeast and have expanded over the south of the state. Similar impacts were also evident over far northern central New South Wales where the area with lowest on record rainfall broadened.
Deficiencies in both northern Queensland and Northern Territory became more severe and slightly more extensive. Conversely, areas of serious to severe rainfall deficiencies remain largely unchanged in Queensland's central interior, Victoria, South Australia and Western Australia.
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Very long term deficiencies persist
The rainfall deficiencies in southern Australia at periods up to 41 months are also evident on much longer timescales. The map of rainfall deficiencies for the past 16 years (the period of the current millennium) 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
In southern Australia soil moisture in the lower layer (from 10 cm to 100 cm deep) for February 2016 showed marked changes from the value in January reported in the previous Drought Summary. Southern Australia generally had average to very much above average soil moisture with the exception of the western half of Tasmania, central South Australia and far southern Victoria where smaller areas of very much below average and below average soil moisture remained.
In northern Australia lower layer soil moisture was generally average to above average in most of the Northern Territory extending into western border area of Queensland, central New South Wales and central inland parts of Western Australia. Queensland's tropical north coast, central coast and adjacent inland areas were average with small areas in the central interior very much above average.
While below average and very much below average soil moisture was evident in northwest Western Australia and in the northern areas of the Top End. In the Cape York Peninsula below average and lowest on record conditions extended further south since January, and lowest on record conditions were evident at the tip.
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.
