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 16 October, rainfall was recorded in all States and Territories.
At the start of the week, a low to middle level cloundband over Victoria and southeastern New South Wales, associated with the passage of a cold front and pre-frontal trough, produced light to moderate falls across Victoria and southeastern New South Wales. A complex surface trough extending around the continent from southwest Western Australia to New South Wales combined with a moist, unsettled air mass and generated large areas of convection with thunderstorms over Central Australia, southern and southeastern Queensland, and much of eastern New South Wales.
By the middle of the week, showers and storms associated with the trough extended around the Gulf Country and southern parts of the Northern Territory. The surface trough interacted with an upper level trough over eastern Queensland and triggered widespread showers, thunderstorms and areas of rain. Moderate falls were reported in northeastern New South Wales, and much of eastern Queensland. Locally heavy falls were reported in the Wide Bay and Burnett District, and parts of southeast Queensland. The severe thunderstorms that developed in the Wide Bay and Burnett produced very large hail, damaging winds along with two separate tornadoes: one at Tansey and the other at Coolabunia.
In the last part of the week, the surface trough shifted offshore but continued to produce showers and moderate falls across much of eastern Queensland and coastal New South Wales. Showers were enhanced about the southern Queensland coast, due to deepening low pressure near the coast, with moderate to locally heavier falls recorded in areas of the southeast Queensland and northeastern New South Wales coasts.
From the middle of the week, a trough near the west coast produced light to moderate falls in the southwest Gascoyne in Western Australia, while a low pressure system and cold front tracked across southern parts of the State in its wake, with moderate falls across the South West Land Division and Goldfields District in Western Australia. Extensive thunderstorm activity developed to the east of the system and brought moderate falls to the southeast of Western Australia and southwest South Australia, with lighter falls recorded in southeastern South Australia and western Victoria as the system traversed eastwards at the end of the week.
Rainfall totals exceeding 100 mm were recorded in southeastern Queensland and northeastern New South Wales, with falls in excess of 200 mm recorded in parts of the Sunshine Coast, the Gold Coast Hinterland, and the Mid North Coast and Northern Rivers in New South Wales. The highest weekly total was 378 mm at Tewantin in southeast Queensland.
Rainfall totals exceeding 50 mm were recorded in areas of northern, central and southeastern Queensland; also about the northeast, central and southeast coast of New South Wales.
Rainfall totals between 10 mm and 50 mm were recorded in southern Western Australia; southern South Australia; southern and central parts of the Northern Territory, extending into the southeastern Kimberley in Western Australia and northwestern South Australia, as well as isolated areas around Darwin; about the Gulf Country; isolated areas of far western Queensland; most of eastern Queensland and New South Wales; eastern, central and western Victoria away from the south coast, and in a small area of northeastern Tasmania.
Little or no rainfall was recorded in the central interior and most of northern Western Australia; most of the Top End in the Northern Territory; northeastern South Australia; northwestern Tasmania; northwestern New South Wales and far southwest Queensland.
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 16 October 2018.
Rainfall for the period 1 April 2018 to 16 October 2018
Serious or severe rainfall deficiencies for the 6-month period persist across 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 areas of the Goldfields District in southern Western Australia; also to a lesser extent across affected areas in southeast Queensland and northeastern New South Wales, and parts of southeastern 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. The coastal south of Western Australia has now received between 80% and 60% of their average, with an area of the central Goldfields reaching 100%, but the percentage of mean rainfall received decreasing to less than 30% 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, and less than 20% of the 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 16 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.
Rainfall in the last week has only slightly eased deficiencies in an area of southeastern New South Wales and northwestern Victoria, and had little impact elsewhere.
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. Much of northwestern New South Wales, southwestern Queensland, and northeastern South Australian having received less than 30% average rainfall for the period, while 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 16 October 2018
For the 18-months starting April 2017, rainfall deficiencies are 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 made very little impact on deficiencies in affected areas.
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