Rainfall deficiencies persist in Western Australia, South Australia, Tasmania and eastern Victoria
Rainfall in July was below average over much of the southern half of mainland Australia away from the southern coastal fringe and southern alpine areas, although most areas were less anomalously dry than they had been in June. Rainfall was very much below average (the lowest 10% on record) across much of the same area with some small patches of lowest on record.
After the exceptionally dry June across Australia (the second-driest June on record for the country as a whole) and below average July rainfall, the first half of the southern wet season (April to November) has been very dry over large parts of eastern and southwestern Australia. Western Australia has a larger spatial area of very much below average rainfall at this April to July period than at the five-month March to July drought period. Areas that received above average rainfall in March are not showing up on the five-month drought map but are dry over the April to July period. These areas include large parts of New South Wales (25% of the State) which are showing up as very much below average for the April to July period. Shorter standard periods are also showing very much below average rainfall with areas of lowest on record at some periods, these will monitored closely for any further developments.
5-month rainfall deficiencies
Compared to the 4-month period ending June 2017, rainfall deficiencies have increased slightly in both areal extent and severity along the west coast of Western Australia, with a large area around and south of the Gascoyne coast observing lowest on record rainfall compared to similar March to July periods.
Rainfall deficiencies persist on the Eyre Peninsula in South Australia, along with the Yorke and Fleurieu peninsulas, parts of the Adelaide region and the mid-North, and on Kangaroo Island. Deficiencies also persist in West Gippsland and adjacent parts of northeastern Victoria. In Tasmania, deficiencies have decreased in spatial extent but increased slightly in severity.
Rainfall deficiencies have decreased markedly across the southern half of the NT into western Queensland following a wet July in these areas. This is a seasonally dry time of year across the region and even small rainfall totals can impact on rainfall deficiencies.
Daytime temperatures were warmer than average over large parts of the country in June and July. The clear skies and the dry, warm air have led to unusually high evaporation rates for winter in many areas, contributing to below average soil moisture in these regions.
Soil moisture in the lower layer (from 10 cm to 100 cm deep) decreased for July compared to June across most of southern Australia inland from the coastal strip and alpine areas. The only areas to observe significant increases in lower layer soil moisture during the month were through southwest Western Australia, parts of south-coastal South Australia and western Tasmania although soil moisture in these regions generally still remains below levels expected for this time of year.
Soil moisture for July was below average for the west and south of Western Australia; most of southern South Australia, except the far southeast; areas of eastern Tasmania; eastern Victoria; areas of inland eastern and northern New South Wales; and much of central Queensland.
- July rainfall below average for much of southern Australia
- Serious to severe rainfall deficiencies are present at the 5-month timescale near the west coast of Western Australia, between the Eyre Peninsula and Adelaide region in South Australia, in western and southern Tasmania, and in West Gippsland in Victoria
- Soil moisture is below average across the west and south of Western Australia, most of southern South Australia, inland New South Wales, eastern Victoria, and parts of Tasmania
Product code: IDCKGD0AR0
Soil moisture details are reported when there are periods of significant rainfall deficits.
Soil moisture data is from the Bureau's Australian Water Resources Assessment Landscape (AWRA-L) model, developed through the Water Information Research and Development Alliance between the Bureau and CSIRO.
See: Australian Landscape Water Balance.
What is drought?
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.
It is generally difficult to compare one drought to another, since each drought differs in the seasonality, location, spatial extent and duration of the associated rainfall deficiencies. Additionally, each drought is accompanied by varying temperatures and soil moisture deficits.
Rainfall averages, variability and trends
- Average rainfall: How much rain do you expect?
- Rainfall variability: How consistent is rainfall in your area?
- Rainfall history: Check tables, graphs and data from your local weather station.
- Rainfall trends: Has your rainfall changed?
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.
For the week to 22 August 2017, rainfall was recorded in the South West Land Division of Western Australia, southern South Australia, southern New South Wales, Victoria, and Tasmania.
At the start of the week, a vigorous cold front and associated cloudband over southeastern Australia connected to a complex low pressure system to the south of the Bight, producing widespread moderate falls in southern South Australia, southern New South Wales, Victoria and western Tasmania, with higher totals about the Alps. Some minor flooding resulted about the Adelaide Hills district and Onkaparinga River while there were river rises in northeastern Victoria. A cold westerly flow in the wake of the cold front continued to produce moderate falls across southeastern South Australia, much of Victoria and western Tasmania until the middle of the week.
From the middle of the week, a cut-off low pressure system and associated cold front developed and slowly tracked across southwest Western Australia and generated moderate falls about Western Australia’s southwestern coastal fringe. In the east, a weak low pressure system and associated cold front crossed southern Victoria and Tasmania, while the complex low moved across the south of Tasmania and into the Tasman Sea, producing a cold, southwesterly flow. This brought mainly light falls to southwestern Tasmania, most of Victoria and elevated areas of southeastern New South Wales. Moderate falls were recorded in parts of central southern Victoria.
At the end of the week, the cut-off low pressure system had tracked into South Australia, with the centre near Adelaide. The system produced showers and thunderstorms about the Eyre and Yorke Peninsulas, Kangaroo Mountain and the Mount Lofty Ranges. Widespread, light falls were recorded across southern South Australia and western Victoria.
Rainfall totals in excess of 100 mm were recorded elevated areas of the Victorian Alps and the Snowy Mountains in New South Wales, and in a small area in western Tasmania. The highest weekly total was 240 mm at Perisher Valley in New South Wales.
Rainfall totals between 50 mm and 100 mm were recorded in the western half of Tasmania, northeastern Victoria, elevated areas in southeastern New South Wales. Similar totals were recorded in small areas of the South Coast district in Western Australia and in southeastern South Australia.
Rainfall totals between 10 mm and 50 mm were recorded in the South West Land Division in Western Australia, in South Australia south of a line from Ceduna to Loxton, Victoria, southern parts of New South Wales, and in the remainder of Tasmania except near the East Coast.
Little or no rainfall was recorded in remaining parts of Western Australia, the northern halves of South Australia and New South Wales, Queensland, and the Northern Territory.
Impact of recent rainfall on deficits
The Drought Statement, issued on 3 August 2017, discusses rainfall deficits over Australia for the 5-month (March 2017–July 2017) period. The rainfall deficit map is available for this period as well as for standard periods.
The maps below show the percentage of mean rainfall that has been received for the rainfall deficit period for the 5-month period ending 22 August 2017.
Rainfall for the period 1 March 2017 to 22 August 2017
Serious or severe rainfall deficiencies persist along the westernmost part of Western Australia, and sections of South Australia including the Eyre Peninsula, Kangaroo Island, and areas of the Yorke Peninsula. Serious deficiencies are also present in southern Tasmania and in South and West Gippsland and adjacent parts of northeastern Victoria.
Rainfall during the last week has slightly eased deficits in South West Western Australia, although rainfall received for the period remains less than 20% of average near the Northwest Cape, rising to more than 80% of average in parts of South West Western Australia.
Recent rainfall has also moderated deficiencies in parts of southern South Australia and eastern Victoria. Rainfall totals are less than 70% of average for northern parts of the Eyre Peninsula in South Australia, and less than 70% of average for much of Gippsland in Victoria. Rainfall totals remain less than 70% in the southeast of Tasmania.
Product code: IDCKGRWAR0