Rainfall deficiencies and water availability
Deficiencies continue in Queensland and Western Australia
Rainfall deficiencies at shorter timescales such as the 10 months from April 2020 to January 2021 continue in parts of southwest to central Western Australia and greater southeastern Queensland. While most of the regions affected by serious or severe rainfall deficiencies received near average or below average rainfall, parts of inland southern Queensland received above average rainfall for January 2021, resulting in a lessening of deficiencies in that area.
Elsewhere in Australia, January rainfall was above average for much of mainland southeast Australia contributing to gradual recovery from longer term multi-year rainfall deficits. Following above average January rainfall over parts of southeast Australia some areas have seen a lessening of rainfall deficiencies for both January 2017 to present and January 2018 to present, most notably over northeastern Victoria and southern to central New South Wales for both periods.
The Annual Climate Statement 2020 reported that 2020 was the fourth warmest year on record for Australia, and that the annual total rainfall was 4% above average. Rainfall during 2020 helped relieve some of the most extreme drought conditions in parts of eastern Australia but more rainfall is needed over an extended period to fully recover from the extended extreme dry conditions of 2017 to 2019.
The Climate Outlook, issued 4 February, indicates February to April 2021 rainfall is likely to be close to or above average for much of Australia, with a greater than 70% chance of above average rainfall for much of Western Australia, northeast Queensland, and parts of southeast Australia, including eastern Tasmania.
10-month rainfall deficiencies
Serious or severe rainfall deficiencies for the 10-month period April 2020–January 2021 are in place in a large area of Western Australia, covering parts of the central South West Land Division, the eastern half of the Gascoyne, and the west of the Goldfields District. Deficiencies remain similar to the previous 9-month period, with little rain falling in January in what is a seasonally dry time of the year for the South West Land Division.
In eastern Australia, rainfall deficiencies have again contracted in Queensland, although serious or severe rainfall deficiencies continue in parts of the greater southeast of the State, covering the Wide Bay and Burnett District, extending in some areas north to around Rockhampton and inland to around Tambo and Charleville. Some areas of southern inland Queensland received above average rainfall for January.
Extended dry conditions over eastern Australia
Australia has experienced a prolonged period of below average rainfall spanning several years.
Rainfall deficiencies have affected much of Australia since January 2017. Multi-year rainfall deficiencies and their impact on the Murray–Darling Basin are discussed in Special Climate Statement 70 and the dry conditions over Eastern Australia for the period commencing January 2018 are described in Special Climate Statement 66. The strip along the west coast and south coast of Western Australia has also been affected by rainfall deficiencies for the periods commencing January 2017 and January 2018.
For periods longer than 24 months, the greatest impact of the prolonged below average rainfall has been in the cooler months of April to October. Large parts of the country remain in severe rainfall deficiency for the 34-month period from April 2018 to January 2021, though rainfall last year and in early 2021 has seen improvement across many areas. Above-average January rainfall eased longer-term deficiencies slightly in parts of the southeast, most notably over northeastern Victoria and southern to central New South Wales. However, in inland Western Australia rainfall deficiencies generally increased compared to the same period ending December 2020.
Persistent, widespread, above average rainfall is needed to lift areas out of deficiency at annual and longer timescales and provide relief from the impacts of this long period of low rainfall (such as renewing water storages). The impact of the longer dry on water resources is still evident, especially in northern parts of the Murray–Darling Basin where total storage levels remain low.
The role of climate change in rainfall reduction over southern Australia and along the Great Dividing Range is discussed in State of the Climate 2020. Parts of southwest, southeast, and eastern Australia—including parts of southeast Queensland and southern and eastern New South Wales—have seen substantial declines in cool-season rainfall in recent decades.
Compared to last month, root-zone soil moisture (in the top 100 cm) has increased across much of southeast Australia and Queensland, but has decreased across much of Western Australia, especially in the west and the north, and also across much of the Northern Territory.
Soil moisture was below average for large parts of the southern third of Western Australia, and parts of the agricultural districts of South Australia, mostly around the southeast. Soils were wetter than average for the month across much of the remainder of Australia: through the eastern interior of Western Australia, most of the Northern Territory and New South Wales, northern and far southern Queensland, southern Victoria, eastern Tasmania, northeastern and southwestern South Australia.
The influence of very low rainfall over longer timescales is still evident in the 16-month soil moisture for October 2019–January 2021, which was very much below average over large areas, predominantly in the west and south of Western Australia.
- Deficiencies continue in the southeastern quarter of Queensland and large areas of the west to central regions of Western Australia
- Accumulated rainfall deficits at multi-year timescales remain significant in many parts of Australia, and may persist for some time
- Root-zone soil moisture has decreased across Western Australia and the Northern Territory, and increased across much of the southeast and Queensland
- Major water storage levels remain low in the northern Murray–Darling Basin
- Northern Australian water storages have started to increase in response to northern rainfall onset
Major water storage levels remain low in the northern Murray–Darling Basin
The total water storage levels in the Murray–Darling Basin decreased in January but remain significantly higher than the same time last year. The total storage fell to 54.1% of capacity at the end of the month, a decrease of 3.9% of capacity since last month, but remains at a much higher level (31.7%) than for the same time last year.
The storage levels in the north differ from those in the south. Total water storage in the northern Basin increased by 3.8% to 27.4% of capacity (1,272 GL) at the end of January, which is 21.4% higher than the same time last year. Despite above average rainfall across most of the southern Basin, the total storage decreased by 5.7% to reach 60.1% (12,423 GL) of capacity; which is still significantly higher than January 2020 when it was only 37.4%.
January rainfall was close to average across most of the northern Basin. However, localised rainfall in the Balonne River basin contributed to large increases in two storages: Lake Kajarabie (Beardmore Dam) by 39% of capacity, and Jack Taylor by 22.4%. These are the only storages in the northern Basin at greater than half of their capacity. Other storages in the north that increased include Keepit (by 14%), Copeton (by 5.5%), Split Rock (6.2%), and Chaffey (by 2%). All other storages in the northern Basin decreased by 1 to 3% in January.
For the southern Basin, the highest percentage decreases in capacity of the major storages in January were for Lake Victoria by 20%, Blowering by 14%, Burrinjuck by 13%, Hume by 12.7%, and Wyangala by 4.2%. All other storages in the southern Basin decreased by 1 to 3% of their capacity. The only exceptions with slight increases were Darthmouth and Lake Cargelligo. Despite the overall decline, some individual storages like Corin, Cotter, Googong, Lake Buffalo, Lake Pamamaroo, Lauriston, and Upper Coliban were above 90% of their capacity.
Northern Australian water storage levels remain low
The northern Australian monsoon season commenced in December and continued through January and, in response, water storages in northern Australia have started to increase. Water levels in Lake Argyle, the largest water supply storage in Australia holding up to 10,400 GL, have been decreasing since September 2017 as the past three wet seasons have not delivered significant inflows to the storage. This year's monsoon has brought some relief and in January, Lake Argyle's storage volume increased by 4.6% to reach 31.4% of its accessible capacity. Wet season filling is also reflected in the Darwin River storage which has increased by 7.4% to reach 59% of its capacity.
The largest storage in South East Queensland, Wivenhoe, has decreased significantly in the past three years and continued to decrease in January to reach to 37.6 % of capacity at the end of the month.
Product code: IDCKGD0AR0
A very dry month for the southeastern mainland increases rainfall deficiencies
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.
For the week to 23 February 2021, rainfall was recorded in northern and central Western Australia; northern parts of the Northern Territory; northern, central and the coastal south-east of Queensland, eastern New South Wales, north-east Victoria and western Tasmania.
At the beginning of the week, a surface-to-low level pressure trough extended across northern Australia to the Coral Sea, with embedded weak tropical lows located in the western Gulf of Carpentaria, and off the north tropical coast of Queensland. Moderate falls were recorded in the far northern Kimberley, in the Top End and the Carpentaria coast in the Northern Territory, and northern Queensland.
A high pressure system in the southern Tasman Sea extended a ridge over southeast Australia, and resulted in moderate falls along the east coast between south-east Queensland and the Mid North Coast in New South Wales.
In the west, an inland trough stretched down to the south coast and produced light to moderate falls in the east Pilbara, and central Western Australia.
In the first part of the week, a weak cold front and a pre-frontal trough moved across southern Western Australia and produced light to moderate falls in the state's far southwest, south coast and the Goldfields.
In the second part of the week, a trough off the east coast of Australia deepened and a low pressure system formed in the northern Tasman Sea, well off the northern New South Wales coast. Moderate falls to locally heavy falls were recorded in coastal south-east Queensland, and the northern to central coasts of New South Wales. The Tasman low moved slowly south to south-east away from Australia by the end of the week.
The trough over northern Australia persisted into the second half of the week, and the tropical low in the Gulf moved west to south-eastern Arnhem Land then across the base of the Top End in the Northern Territory. A weak tropical low formed off the Kimberley coast at the end of week. Showers and thunderstorms continued in the north streching from the Pilbara and Kimberley in Western Australia, through northern parts of the Northern Territory and Gulf country, across Cape York Peninsula to the north tropical coast in Queensland. Locally heaver falls in excess of 100 mm to 200 mm were recorded in the north tropical coast in Queensland, and the Carpentaria coast in the Northern Territory.
A high pressure system in the Great Australian Bight directed onshore flows, with light to moderate falls to in south-east Australia at the end of the week.
Rainfall totals in excess of 200 mm were reported in southern parts of the torth tropical coast in Queensland, the Carpentaria coast and along the base of the Top End in the Northern Territory. The highest weekly total was 709 mm at Tully Sugar Mill in Queensland.
Rainfall totals between 50 mm and 200 mm were reported over northern parts of the Northern Territory, across the Gulf country, Cape York Peninsula, northern Goldfields and North Tropical Coast in Queensland. Similar rainfall totals were also recorded in the Northern Rivers and Mid North Coast districts in New South Wales.
Rainfall totals between 10 mm and 50 mm were recorded in the Kimberley, Pilbara and south to the Goldfields and Southeast Coastal districts in Western Australia, across northern parts of the Northern Territory, northern, central and south-east Queensland, along the east of New South Wales, north-east Victoria and south-west Tasmania.
Impact of recent rainfall on deficits
Rainfall deficits over Australia for the 10-month (April 2020–January 2021) period are discussed in the Drought Statement, issued on 5 February 2021.
Rainfall deficit maps are available for this period as well as for standard periods. The map below shows the percentage of mean rainfall that has been received for the rainfall deficit period starting April 2020 and extended to the week ending 23 February 2021.
Rainfall for the period 1 April 2020 to 23 February 2021
Serious or severe rainfall deficiencies for the period starting 1 April 2020 are in place in Western Australia across large parts of the southern half of the State, excluding the western Gascoyne and southern parts of the South West Land Division (SWLD). Serious rainfall deficiencies are also affecting greater south-east Queensland.
Some inland areas of Western Australia have received less than 50% their average for the period, while areas in the northern SWLD have generally received less than 80% of their average for the period. Remaining areas in Western Australia have and areas in south-east Queensland and have generally received less than 60% of their average for the period.
Product code: IDCKGRWAR0