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 ending 15 August 2017, rainfall was recorded in southern and western Western Australia, Victoria and coastal South Australia, across Tasmania, and in pockets of Cape York Peninsula.
The week began with a strong cold front and associated cloud band moving across Western Australia, and a weak trough passing over Tasmania and southern Victoria. Heavy falls were recorded across the South West Land Division of Western Australia, with lighter falls in the surrounding areas as well as in eastern Victoria, southeastern New South Wales and western Tasmania. Additional light rain also fell around Cape Melville in northern Queensland in response to moist onshore airflow.
By the middle of the week, the strong cold front had moved over eastern Australia, with a low pressure system in its wake. The combination produced light falls along the coast of South Australia and western Victoria, with heavier falls in Tasmania, particularly in the west.
A series of cold fronts crossed the southwestern tip of Western Australia in quick succession towards the end of the week, delivering rain to the western as far north as Kalbarri on the Gascoyne coast and inland to the Goldfields District. As the fronts migrated to the east they also delivered small totals to southern South Australia, western Tasmania and Victoria.
Rainfall totals of more than 50 mm for the week were recorded in the highlands of western Tasmania and the west of the South West Land Division in Western Australia. Areas of higher falls in excess of 150 mm were observed around and south of Perth, including the highest weekly total of 177 mm at Huntly.
Weekly totals of between 25 and 50 mm were recorded in the remainder of the South West Land Division in Western Australia, central and northeastern Tasmania, pockets of the Alpine area of Victoria and the southern coastlines of Victoria and South Australia.
Rainfall totals between 10 and 25 mm were reported around the regions of higher totals across the Southeast Coastal, Gascoyne and Goldfields districts in Western Australia, parts of coastal South Australia, parts of eastern coastal Tasmania, isolated pockets of eastern Cape York Peninsula, and areas of Victoria in the southwest, as well as between the Alps and Mornington and Wilsons Promontory peninsulas.
Little to no rainfall was recorded in northern and eastern Western Australia, the Northern Territory, Queensland, and most of South Australia and New South Wales.
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 15 August 2017.
Rainfall for the period 1 March 2017 to 15 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 eased deficits in 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. Rainfall totals are less than 70% of average for parts of the Eyre Peninsula in South Australia, and less than 60% of average for parts of West Gippsland. Rainfall totals are less than 80% for western Tasmania, but less than 60% in the southeast of Tasmania.
Product code: IDCKGRWAR0