Australia's driest September on record increases rainfall deficiencies
September rainfall was below average across the majority of Australia, and especially so across the southern mainland. It was the driest September on record nationally, and the second driest September on record for Victoria, third driest for Western Australia, and fourth driest for South Australia.
Rainfall totals were in the lowest 10% of historical rainfall totals for the month in large areas including greater southwestern Western Australia (southwest of a line between about Geraldton and Esperance), South Australia from Ceduna east across the Eyre Peninsula and agricultural districts, much of the western half of New South Wales, and nearly all of Victoria except parts of South and West Gippsland. Total rainfall for the month was the lowest on record for September at many sites in Victoria and Western Australia, and a handful of locations in New South Wales and Tasmania.
The year to date has also been exceptionally dry over the mainland southeast, with significant rainfall deficiencies continuing to affect large areas of eastern Australia at timescales out to around two years duration. Compared to other January to September periods since 1900, year-to-date rainfall has been the second lowest on record for the Murray–Darling Basin, third lowest for New South Wales, and eighth lowest for Victoria.
Deficiencies have increased in both extent and severity at each of the 6-, 9- and 18-month timescales across eastern Australia and parts of Western Australia. Deficiencies have increased for much of New South Wales, with the area of severe deficiencies now extending further into eastern and northern Victoria, eastern South Australia, inland southern Queensland, and south coast Western Australia than compared to periods ending August 2018.
Accompanying recent low rainfall have been unusually high day-time temperatures, which add to the impact of reduced rainfall, e.g. as seen through reduced soil moisture. Australian maximum temperatures for 2018 to date have been the second warmest on record with an anomaly of +1.36 °C (behind 2013 with an anomaly of +1.54 °C). Both New South Wales (+2.17 °C) and the Murray–Darling Basin (+2.10 °C) have experienced their warmest January–September period on record.
6-month rainfall deficiencies
The southern rainfall season spans April to November and corresponds to the southern agricultural cropping season. For 2018, the southern rainfall season to date has so far seen 6 consecutive months of below average rainfall across much of Australia. Serious or severe rainfall deficiencies persist across much of the eastern mainland, affecting northern and eastern Victoria, nearly all of New South Wales except along the northern coast and a pocket of the central inland north, large areas of Queensland apart from the inland northwest to Gulf Coast region, and eastern South Australia between about Adelaide and the New South Wales/Queensland border. A large area of northwestern New South Wales, and smaller pockets in the southwest New South Wales and along the ranges in the east of the State, and in southwestern Queensland, have received lowest on record total rainfall for the six months April to September 2018.
Large areas of serious or severe rainfall deficiencies are also in place for Central Australia and Western Australia's Interior District, and across an area along the south coast of Western Australia and much of the southern Goldfields District.
Compared to the 5-month period ending August 2018, deficiencies have increased in severity across southern Western Australia, eastern South Australia, northern and eastern Victoria, and much of the affected areas of New South Wales and Queensland, particularly in western New South Wales and southern Queensland.
9-month rainfall deficiencies
For the year to date, deficiencies have increased in severity across southeastern Australia to southern Queensland, and on the south coast of Western Australia. The area affected by deficiencies has expanded between Albany and Hopetoun in Western Australia, and in central southern Victoria. Across the east of South Australia (but excluding the far southeast), northern and eastern Victoria, New South Wales (excluding the northern coast), inland southern Queensland, and a pocket of Queensland adjacent to and inland of Mackay serious or severe deficiencies persist, and have generally increased in strength.
18-month rainfall deficiencies
Similar to deficiencies for other monitored periods in this Drought Statement, rainfall deficiencies have increased across nearly all affected areas for the 18 months commencing April 2017, although changes in absolute severity are smaller than for shorter periods due to the larger total accumulated rainfall deficits over the longer period.
Serious or severe rainfall deficiencies are in place across most of New South Wales except the northeast and parts of the southern border country, across eastern to central southern Victoria, much of southern, central inland, and southwestern Queensland, much of eastern South Australia except the far southeast, and along parts of the west and south coast of Western Australia.
Compared to the 17-month period ending August 2018, the area affected by deficiencies has increased in south coast Western Australia, now reaching to Busselton and inland towards Kalgoorlie, across the northern Eyre Peninsula and Murraylands and Riverland districts of South Australia, across southern New South Wales, and in central southern Victoria.
Following a very dry September, lower-layer soil moisture (from 10 cm to 100 cm deep) has decreased over much of Australia. Warmer than average maximum temperatures and high potential evapotranspiration again contributed to low soil moisture.
Soil moisture for September was below average for most of the eastern mainland States, except southwestern Victoria and parts of Queensland's northwest to central inland north. Below average soil moisture extended into eastern South Australia, affecting areas adjacent to northwest Victoria and reaching the eastern Eyre Peninsula and north to Lake Eyre / Kati Thanda, and also affected most of the Northern Territory and the Kimberley in Western Australia. Parts of the western half of Western Australia, particularly inland areas and along the south coast, also observed below average soil moisture for the month.
- September was Australia's driest on record
- Rainfall was very much below average nationally, and particularly low across the southern mainland
- Rainfall deficiencies have increased across eastern Australia and southern coastal areas of Western Australia at each of the 6-, 9- and 18-month timescales
- Lower-level soil moisture was below average for September across eastern and northern Australia, and parts of inland and southern Western Australia
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 9 October, rainfall was recorded across southern Western Australia; South Australia away from the far northwest and northeast; western and eastern Victoria; most of Tasmania, most of New South Wales; and southeast Queensland.
During the first few days of the week, an upper level trough and associated surface trough extended from northwest and central Queensland into western New South Wales. A low pressure system developed in northern central New South Wales and moved slowly towards the northeast coast and brought isolated thunderstorms and widespread rain over almost all of New South Wales and into southeast Queensland. Moderate falls were recorded in the Lower Western and Central West Slopes districts, as well as in smaller areas along the east coast of New South Wales and through southeast Queensland. Light to moderate falls continued over coastal regions as the low lingered near the coast well into the middle of the week.
In the west, a low pressure system near the southwest coast, and associated broad surface trough, moved slowly eastward over Western Australia during the first half of the week. The systems produced thunderstorms and moderate rain over the Goldfields and Southeast Coast districts, and lighter falls across the southwest and Nullarbor regions of Western Australia.
At the end of the week, troughs extending around the northern coasts of Australia and from the Kimberley through Central Australia to far southeast South Australia, were associated with extensive cloud and embedded thunderstorms. Mostly light falls were observed along a band extending from the west of the Northern Territory to western Victoria, though isolated locations received moderate totals. In the last day of the week a cold front crossing Tasmania and areas of low pressure over the mainland southeast also contributed.
Meanwhile the eastern end of the trough and the low pressure system lingering off the New South Wales Coast, saw continued falls from southeast Queensland to central coast New South Wales.
Rainfall totals exceeding 50 mm were recorded along the coast of New South Wales from Port Macquarie to the Illawarra. Totals in excess of 100 mm were observed at several locations, including the highest weekly total of 297 mm at Careys Peak in the Upper Hunter region of New South Wales. Isolated rainfall totals in excess of 50 mm were also recorded at some locations in the Capricornia, east Darling Downs and Southeast Coast districts of Queensland.
Rainfall totals between 10 mm and 50 mm were recorded in much of the southern South West Land Division, Southeast Coastal and southern Goldfields districts in Western Australia; patches of inland southern, central northern and far southeast regions of South Australia; pockets in western and far eastern Victoria; western Tasmania; southwest, central and eastern New South Wales; and southeast Queensland. An area of Western Australia from the southern Goldfields to the coast around Esperance observed totals in excess of 25 mm for the week, as did areas in a band through inland eastern to western New South Wales, though as the falls were associated with storms and showers coverage was patchy.
Little to no rainfall was observed over northern Western Australia; almost all of the Northern Territory; northwest and northeast South Australia; the central third of Victoria; parts of eastern Tasmania; and most of Queensland away from the southeast.
Impact of recent rainfall on deficits
The Drought Statement, issued on the 3 October 2018, discussed rainfall deficits over Australia for the 6-month (April–September 2018), the 9-month (January–September 2018) and 18-month (April 2017–September 2018) periods. Rainfall deficit maps are available for these periods 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 6-month, 9-month and 18-month periods ending 9 October 2018.
Rainfall for the period 1 April 2018 to 9 October 2018
Serious or severe rainfall deficiencies for the 6-month period persist across much of the eastern mainland, affecting northern and eastern Victoria, nearly all of New South Wales, large parts of southern, western, and eastern Queensland, and much of eastern South Australia away from the far southeast.
Large areas of serious or severe rainfall deficiencies are also in place for Central Australia and areas of Western Australia's interior, south coast, and the south of the Goldfields District.
Rainfall during the last week has somewhat reduced the severity of deficiencies across southern Western Australia, and has also reduced deficiencies to a lesser extent across much southeast Queensland and New South Wales.
Affected areas of northern and eastern Victoria and agricultural South Australia have generally received between 70% and 40% of average rainfall for the period. While the coastal south of Western Australia has now received between 80% and 60% of their average, the percentage of mean rainfall received decreased further inland. Most of New South Wales, inland eastern South Australia, and southern and eastern Queensland have received less than 50% of average rainfall for the period, though large areas of these States have received less than 40% of their mean, and totals still drop to less than 20% of mean for a large area spanning northwestern New South Wales, Queensland away from the southeast quadrant, and Central Australia.
Rainfall for the period 1 January 2018 to 9 October 2018
Serious to severe rainfall deficiencies for the 9-month period are evident across nearly all of New South Wales, except the northern coast, much of northern, southern central, and eastern Victoria, large parts of southern Queensland, and much of eastern South Australia except the far southeast. Since last month, an area of rainfall deficiencies have also developed on the south coast of Western Australia, between Albany and Hopetoun.
Rainfall in the last week has slightly reduced the extent of serious deficiencies for this period through much of New South Wales, eastern South Australia, and southeastern Queensland. In Victoria away from western regions which received rainfall this week, deficiencies have generally increased slightly.
Affected parts of Victoria, eastern New South Wales, and agricultural districts of South Australia have generally received between 70% and 40% of average rainfall for the period. Percentage of average rainfall received drops further inland, with much a large area of northwestern New South Wales, southwestern Queensland, and northeastern South Australian having received less than 30% average rainfall for the period. The affected area on the south coast of Western Australia has received between 80% and 60% of the average.
Rainfall for the period 1 April 2017 to 9 October 2018
For the 18-months starting April 2017, rainfall deficiencies are still present over most of New South Wales away from the northeast coast and southern border; across eastern to central southern Victoria; southern, central, and southwestern Queensland, much of eastern South Australia except the far southeast, and along parts of the western and southern coast of Western Australia.
Recent during the past week has slightly reduced deficiencies at this timescale in the south of Western Australia, across southwestern and central New South Wales, and some parts of southeast Queensland.
Rainfall in affected areas of Western Australia, Victoria, agricultural districts of South Australia, southern New South Wales, and southeastern Queensland has generally been between 80% and 60% of average for the period. Percentages of mean rainfall have generally decreased further inland, with large areas of New South Wales away from the south and northeast, northeastern South Australia, and southwestern Queensland having received between 60% and 30% of average rainfall for the period.
Product code: IDCKGRWAR0