Issued 7 June 2016

Rainfall deficiencies continue in some areas

After many months of mostly below-average rainfall, the start of the northern dry season saw very much above-average rainfall during May over much of northern Australia and central parts of the country. May rainfall was up to four times the climatological average over the Kimberley, the Top End, the western two-thirds of Cape York and the Corner Country. This included record-breaking daily rainfall totals over parts of northern and central Australia. Above-average rainfall also fell across the southeast away from the coast. All States and Territories had above average May rainfall, with Tasmania recording its third-wettest May on record.

May's rainfall has reduced many of the deficiencies evident at the 12-month timescale in the previous Drought Statement. This includes the removal of deficiencies in much of Tasmania, along with improvements in southeast South Australia and western Victoria. Deficiencies in northern Australia, central Queensland and southwest Western Australia have contracted though remain severe in some areas.

In many parts of the country, rainfall has been below average for much of the last four years, and in some areas for most of the last sixteen years or more. The rainfall deficits that have accumulated in these areas are very large, and their removal will require above average rainfall over a sustained period.

13-month rainfall deficiencies

May's rainfall has reduced many of the deficiencies evident at the 12-month timescale in the previous Drought Statement. This includes a significant contraction of the deficiency affecting Tasmania, with only a small area in the northwest now affected by severe deficiency. In Victoria, the severity in the Mallee has reduced to serious deficiency and the deficiency on the Yorke Peninsula in South Australia has been removed. Large parts of southwestern Victoria and far southeast South Australia exhibit serious to severe deficiency at the 13-month timescale.

The area of deficiency in southwest Western Australia has contracted. In the Pilbara and Kimberley only pockets of deficiency are evident near the coast. In the Gascoyne, the area of deficiency has extended further inland and the severity has increased from serious to severe near the coast.

Deficiencies in northern Australia have contracted substantially, although areas of severe deficiency remain near the coast in the Top End. The severe deficiency areas in Cape York Peninsula have shown an improvement and the area affected has contracted.

In Queensland's Central West, areas of severe deficiency still exist at the 13-month timescale, but have eased slightly. There are other patches of serious deficiency scattered through Queensland and near the Gulf of Carpentaria.

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Longer-term deficits in Victoria, Tasmania, Queensland and northern New South Wales

Since the most recent La Niña concluded in autumn 2012, rainfall has generally been much below average over large parts of Queensland and into northern New South Wales, and also over western Victoria and Tasmania. The most recent wet season provided rain to some, though not all, parts of the affected areas of Queensland. There was late autumn rain in Victoria and western Tasmania.

The rainfall deficits that have accumulated over the past four years in these areas are now very large, and it will take at least one season with near-average rainfall to remove them. Rainfall analyses for standard periods out to 36 months are available on our web site.

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Very long-term deficits in southern and eastern Australia

Rainfall in much of southern and eastern Australia has been generally below the long-term average since at least the beginning of this century. The period starting in January 2000 has been the driest such period on record in large parts of southwest Western Australia, and very much below average over much of southeast South Australia, Victoria, Tasmania, southern New South Wales and southeast Queensland. It has also been the warmest such period on record in these areas. Conversely, rainfall in northwestern Australia has been very high during the same period.

Southern Australia typically gets significant rainfall from autumn through spring from cold fronts and low pressure systems. However, this activity has substantially decreased in Australia over recent decades, as high pressure systems have become more dominant. This suggests the tendency for recurrent dry conditions is less related to natural climate drivers such as El Niño, and increasingly due to changes in the climate. Research suggests that long-term drying trends over southern Australia cannot be explained by natural variability alone. Comprehensive reports on changes in Australia's climate are available at the Climate Change in Australia website.

These very long-term deficiencies are most significant for slow processes such as the recharge of surface and groundwater storages, and the drying of forests and other parts of the landscape. When rainfall deficiencies are seen over such long timescales they are usually associated with marked impacts on water availability. A near-average season may provide enough rainfall for some agricultural applications but would not be enough to relieve the impacts of these long-term deficiencies on water supplies.

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Soil moisture

A wetter than average May in many parts of the country has increased the relative amount of available soil moisture in the lower layer (from 10 cm to 100 cm deep) in those areas. Soil moisture is now above average in a broad band extending from northwestern Western Australia, through the southern Northern Territory and northern South Australia into southwest Queensland, western and central New South Wales. In that band some areas of very much above average soil moisture are apparent, especially in Western Australia and South Australia. Soil moisture for May was also above average in parts of southwest Western Australia. In Victoria and Tasmania, soil moisture has increased to be near average in most areas, although pockets of below average remain.

Soil moisture remains below average in an area extending from the Central West of Queensland and south into coastal and adjacent inland areas of New South Wales, with well below average soil moisture in parts of some parts. Below average soil moisture is also evident in Western Australia's Gascoyne district, with western areas very much below average. Patches of below average soil moisture are also evident in patches through southeastern Western Australia, southern South Australia, southern Victoria and western Tasmania. Parts of the Top End and Cape York Peninsula also had below or very much below average soil moisture for May.

Soil moisture information presented here is from the Bureau's operational Australian Water Resources Assessment Landscape (AWRA-L) model.

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Definitions

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%.

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.

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