Driest September on record for Murray–Darling Basin exacerbates deficiencies in eastern Australia
Rainfall in September was below average for most of Queensland south of the Cape York Peninsula, New South Wales, northern and far eastern Victoria, South Australia south of Lake Eyre and east of Ceduna, and eastern Tasmania. Below average rainfall was also observed in the Kimberley and northern half of the Northern Territory, however much of northern Australia away from eastern Queensland is typically seasonally dry at this time of year.
Rainfall was very much below average (ranked in the lowest 10% of records) for a large area of the mainland southeast. For New South Wales as a whole September rainfall was the lowest on record, while for Queensland it was the tenth-driest September since records commenced in 1900. Rainfall deficiencies have increased in both extent and severity across eastern Australia at the 4- and 7-month timescales, most notably in New South Wales and the southern third of Queensland.
Dry conditions have been exacerbated by exceptional warmth across most of the country in September, following on from the warmest winter mean maximum temperature on record. Maxima for Queensland were the second-warmest on record for the month, and the sixth-warmest on record for September for New South Wales since records commenced in 1910.
4-month rainfall deficiencies
Serious to severe rainfall deficiencies are present across an area of South Australia extending from the top of the Great Australian Bight through northern agricultural and southern pastoral districts to the western border of New South Wales; across most of New South Wales except parts of the northwest and northeast; large parts of Queensland between the southern border, Fraser Island, and the Central Coast; an area of central Victoria and East Gippsland; and east coast Tasmania.
Serious to severe rainfall deficiencies for the 4-month period ending September 2017 are present in areas along the northwestern coast between the Gascoyne in Western Australia and the western Top End in the Northern Territory. Rainfall during September alleviated deficiencies in parts of the Gascoyne and across areas further south.
Deficiencies have increased in both areal extent and severity since last month across affected areas of South Australia, Victoria, New South Wales, and Queensland.
7-month rainfall deficiencies
Rainfall deficiencies persist along the west coast of Western Australia between about Exmouth and Perth, although rainfall during September has moderated the severity of deficiencies slightly, and reduced their extent across the southwest of the State. Unseasonal September rainfall in Central Australia has also reduced the extent of deficiencies in the south of the Northern Territory.
Compared to the 6-month period ending August 2017, deficiencies have increased in areal extent in the mainland eastern States. Rainfall deficiencies affect areas of coastal South Australia between the Nullarbor and Eyre Peninsula, East Gippsland in Victoria, the east coast of Tasmania, pockets of central to western New South Wales, and across most of central to southwestern Queensland. However, this is a seasonally dry time across inland Queensland and Central Australia, and little change is expected in these regions until the northern wet season commences in the comming weeks.
High evaporation rates associated with exceptionally warm September days, clear skies, and low rainfall have again seen a month-on-month decrease in lower-layer soil moisture across much of eastern Australia and South Australia.
Soil moisture in the lower layer (from 10 cm to 100 cm deep) for September was below average for most of South Australia (except for coastal areas from the Eyre Peninsula to southeast, and central northern areas); eastern Victoria; eastern Tasmania; nearly all of New South Wales; and most of Queensland south of the Cape York Peninsula (except for parts of the central west and some pockets in the eastern hinterland). Soil moisture was also below average for an area of the Pilbara coast in Western Australia, parts of southern Western Australia, and the far south of the Northern Territory.
Conversely, soil moisture has increased across much of Western Australia and was above average for September in much of the Gascoyne and south of the Interior District, as well as being above average in scattered pockets of Central Australia, west coast Tasmania, and coastal southwestern Victoria.
- Rainfall during September was below to very much below average over much of Australia, and lowest on record for the Murray–Darling Basin as a whole
- Serious to severe deficiencies are present at the 4-month timescale across the majority of New South Wales, parts of southern, central and east coast Queensland, a large area of central southern South Australia, coastal parts of northwest and northern Western Australia and the western Top End, eastern Victoria, and eastern coastal areas of Tasmania
- Serious to severe rainfall deficiencies are evident at the 7-month timescale near the west coast of Western Australia, west coast South Australia, eastern Tasmania, and pockets of eastern Australia from eastern Victoria to central and southwestern Queensland
- Lower-layer soil moisture for September was below average across most of South Australia, Victoria, New South Wales and Queensland, the south of the Northern Territory, eastern Tasmania, and areas of the south of 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 17 October 2017 rainfall was recorded in all States and Territories.
At the start of the week, a broad surface trough through central parts of the county was associated with thunderstorm activity, generating moderate falls in Central Australia and parts of southwestern South Australia. The surface feature interacted with an upper-level disturbance, with an extensive cloudband and embedded thunderstorms extending from the northern interior through South Australia, into southeastern Australia. Widespread moderate falls were recorded in southern Queensland, most of New South Wales, Victoria, Tasmania and eastern South Australia.
The surface trough migrated eastwards and deepened, extending across inland Queensland through the middle of the week while a series of upper level troughs maintained instability over much of the State. Moderate to locally heavy falls resulted in central to southeast Queensland, and in the north central coast of New South Wales.
A broad area of low pressure also produced convective cloud with thunderstorms developing about the northern Kimberley, western areas of the Northern Territory, and around Alice Springs in the middle of the week.
A surface trough then rapidly deepened near the west coast of Western Australia, with thunderstorms and showers developing near the trough. Isolated, moderate to locally heavy falls were recorded in the northern South West Land Division, through the central interior, eastern parts of the Pilbara, and the northern Kimberley.
During the last part of the week, the surface trough stretching across Queensland’s interior shifted west, extending a moist air mass through most of the State. An upper level low over the southern interior combined with the air mass, resulting in showers and storms over most of eastern Queensland and northeastern New South Wales. The upper level disturbance shifted slowly northwards and into the northeast tropics, while a low level trough moved westwards across the Coral Sea towards the east tropical and Capricornia coasts. Moderate to heavy falls were recorded about the Sunshine Coast and Wide Bay and Burnett District. Further moderate to locally heavy falls were recorded between Cape York Peninsula and northeastern New South Wales, as well as lighter falls about the Gulf and Top End. In the west, a strong cold front produced moderate rainfall in southwest Western Australia
Rainfall totals exceeding 200 mm were recorded in parts of the Wide Bay and Sunshine Coast areas in southeast Queensland. The highest weekly total was 304 mm at Eumundi in southeast Queensland. Rainfall totals in excess of 150 mm were recorded between Seventeen Seventy and Caloundra in southeast Queensland, and around Murwillumbah in the Northern Rivers District, and about Coffs Harbour in the Mid North Coast District of New South Wales.
Rainfall totals between 50 mm and 150 mm were recorded in parts of Queensland around Cooktown in the eastern Cape York Peninsula, in pockets from the north tropical coast to central Queensland, and a large area from central Queensland down to northeastern New South Wales. Similar totals were recorded in isolated locations in Queensland’s Gulf Country, the Central Wheat Belt in Western Australia, southwest South Australia and western Tasmania.
Rainfall totals between 10 mm and 50 mm were recorded in parts of the Kimberley, central and southwest Western Australia; in the Top End and the west of the Northern Territory; in southwestern and parts of eastern South Australia; western, central and much of northern Victoria, and western and northern Tasmania. Similar totals were recorded in southern and northeastern New South Wales, and surrounding higher falls in eastern and northern Queensland.
Little or no rainfall was recorded in the northwest and east of Western Australia, south of the Kimberley, western and most of northern South Australia, much of the eastern half of the Northern Territory, western Queensland, northwest and southeast New South Wales, and a small area of eastern Victoria.
Impact of recent rainfall on deficits
The Drought Statement, issued on 4 October 2017, discusses rainfall deficits over Australia for the 7-month (March 2017–September 2017) and 4-month (June 2017–September 2017) periods. 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 4- and 7-month periods ending 17 October 2017.
Rainfall for the period 1 March to 17 October 2017
Serious to severe deficiencies are present at the 4-month timescale across northern agricultural and southern pastoral districts of South Australia; most of New South Wales except parts of the northwest and northeast; large parts of the southeastern half of Queensland; an area of central Victoria and East Gippsland; and east coast Tasmania. Deficiencies are also present in areas along the northwestern coast between the Gascoyne in Western Australia and the western Top End in the Northern Territory.
Rainfall in the past week has done little to relieve deficiencies in these affected areas.
The affected area in the Gascoyne has received between 30% and 50% of average rainfall for the period, while seasonally dry areas further north have received less than 30% of average. Affected areas of South Australia less than 60% of average, and in western New South Wales less than 50% of average. Rainfall less than 60% of average was also observed in affected parts of Victoria and Tasmania. In Queensland affected areas in the north and west recorded less than 30% of average, and up to around 60% of average in areas towards the southeast.
Rainfall for the period 1 June 2017 to 17 October 2017
Serious to severe rainfall deficiencies persist at the 7-month timescale near the west coast of Western Australia between about Exmouth and Perth, areas of coastal South Australia between the Nullarbor and Eyre Peninsula, east coast Tasmania, and pockets of eastern Australia between East Gippsland in Victoria and central to southwestern Queensland.
Rainfall in the past week has eased deficiencies in some affected areas, including the eastern Pilbara in Western Australia, southern and eastern Queensland and parts of western New South Wales. Many areas along the eastern coast, adjacent inland districts, and the southern interior of Queensland have now received at least 100% of their average rainfall for the period.
The west coast of Western Australia has received between 30% and 60% of average rainfall for the period, with the higher percentages in the areas further south and lower in much of the seasonally dry north. Affected parts of South Australia, eastern Victoria, and the southeast of Tasmania have received less than 60% of average. Rainfall in affected parts of New South Wales has generally been less than 50% of average, but below 40% of average in many regions.
Product code: IDCKGRWAR0