Issued 5 February 2016

January rainfall has some effect on rainfall deficiencies

Rainfall in January was above average for most of the southern half of the country, with totals well above average in southwest Western Australia, central and south coastal New South Wales, and eastern and northern Tasmania. Rainfall deficiencies eased in areas that received significant rain, but deficiencies at various timescales, as reported in the previous Drought Statement, continue in several areas. Below-average rain was recorded in the tropical north, resulting in the emergence of some areas of rainfall deficiency there. Rain from ex-tropical cyclone Stan in the first few days of Feburary may have eased deficiencies in parts of southern South Australia; this will be reported in next month's drought statement.

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.

9-month rainfall deficiencies

January's rain has seen some contraction of the areas affected by rainfall deficiencies in the period starting in May 2015. The area affected in southwest Western Australia has contracted toward the west, eastern Tasmania is no longer experiencing severe deficiencies, northwestern Victoria is no longer experiencing serious deficiencies, and deficiencies previously present in northwest Western Australia have been removed completely. There have been some changes around the margins of areas of deficiency in Queensland and South Australia.

However, serious to severe deficiencies have emerged near the tip of Cape York and northeast of Darwin. Areas of serious to severe deficiency remain in southwest Western Australia, southeast South Australia into southwest Victoria, western Tasmania, and inland from Queensland's Central Coast. Although evident at the 9-month timescale, deficiencies in South Australia, Victoria and Tasmania are particularly marked in the 6-month period starting in August 2015.

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19-month rainfall deficiencies

January's rain had some impact on deficiencies in the period starting July 2014, though not enough to remove them with serious to severe deficiencies (lowest 5% to lowest 10% of records) remaining in parts of southwest Western Australia, southern South Australia, western Victoria and into Tasmania, and in Queensland from the Central Coast inland toward Longreach.

In southwest Western Australia, the area affected by severe deficiency over this period contracted, with significant areas of serious deficiency remaining established. A similar story holds in northwestern Victoria, and in Queensland. Serious to severe deficiencies have eased over eastern Tasmania, but remain in the west. Some areas of serious deficiency have emerged around the Gulf of Carpentaria.

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40-month rainfall deficiencies

The period starting in October 2012, which now runs to 40 months, show serious to severe rainfall deficiencies have slightly eased or contracted over the last month.

Areas of serious to severe deficiency remain across much of Queensland south of Cape York and away from the southeast, in a zone from southeastern South Australia across the western half of Victoria, and in parts of western and southeast Tasmania. The area affected in southwest Western Australia has seen an easing and contraction of deficiencies but they still remain in place along coastal areas.

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Very long term deficiencies persist

The rainfall deficiencies in southern Australia at periods up to 40 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

Soil moisture for January 2016 in the lower layer (from 10 cm to 100 cm deep) was very much below average over Tasmania and southwestern Victoria, with some areas lowest on record. Below-average soil moisture was evident across southern South Australia, in northwest Western Australia, in the northern parts of the Northern Territory, and in parts of eastern Queensland.

Lower layer soil moisture was generally above average in a broad band from southwest Western Australia, through northern South Australia and most of the Northern Territory, and into western Queensland and much of Cape York. Above-average soil moisture was also evident near the Central and far southern coasts of New South Wales.

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.