Rainfall deficiencies and water availability
Above average August rainfall lessens some short-term deficiencies, but little relief in WA
Rainfall during August 2020 was above average for large areas, and very much above average through parts of the interior of the continent, south coast Western Australia, and parts of south-east New South Wales, eastern Victoria, and east coast Tasmania. This resulted in a reduction of rainfall deficiencies at shorter timescales (e.g. the 5 months to August 2020), although there has been little change at longer multi-year timescales.
Daytime temperatures during August were warmer than average for much of the country; the maximum temperature was the sixth-highest on record for August for Australia as a whole, and follows Australia's seventh-highest mean maximum temperature for July during the preceding month.
The Climate Outlook for spring, issued 3 September, indicates an increased chance of wetter than average conditions across the eastern two thirds of Australia but drier than average for west coast Tasmania, and large parts of west and north-west Western Australia. The Bureau will continue to closely watch and report on observed rainfall and seasonal outlooks over coming months.
5-month rainfall deficiencies
Above average rainfall through much of the interior of Australia during August has cleared short-term deficits from central southern and southwest Queensland, and nearly all of the pastoral areas of South Australia at the 5-month timescale. While heavy rain between Albany and Esperance in south coastal Western Australia has removed short-term deficiencies along the coastal strip but had little impact on longer-term deficiencies such as discussed in "Extended dry conditions over eastern Australia" below.
Serious or severe rainfall deficiencies for the 5-month period April–August 2020 are in place in Western Australia across most of the south-western half of the State, excluding parts of the Gascoyne, south coast and Central West District. Serious rainfall deficiencies are also affecting parts of south-east Queensland.
However, at the slightly shorter 4-month timescale (May–August 2020) deficiencies still persist in some parts of South Australia around Spencer Gulf, and also affect northern Tasmania. Much of south-eastern Australia received above average rainfall for April, keeping these areas out of deficiency at slightly longer timescales including April, but have generally received below average rainfall since then.
Most of southern Australia receives the bulk of its annual rainfall during the cooler months of the year. As outlined in State of the Climate 2018, April–October rainfall has declined by 15 to 20% over southern Australia since the 1970s. Rainfall during the past three southern wet seasons was below average, and the first half of the 2020 wet season was also drier than average (relative to 1961–1990). Consecutive poor wet seasons in agricultural regions can amplify the impact of rainfall deficiencies on economic and social systems.
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 early 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.
The greatest extent of rainfall deficiencies over periods longer than 24 months is for the period commencing April 2018. Over half of the country is in severe rainfall deficiency for the 29-month period from April 2018 to August 2020. Regions affected include south-east Queensland, pastoral South Australia, most of south-west Western Australia, and much of the Northern Territory and Central Australia.
The size of the rainfall deficit accumulated over annual and longer timescales remains very large over much of Australia. Despite above average rainfall for much of southeastern Australia and parts of the inland northwest and Northern Territory during one or more months this year, serious or severe longer-term rainfall deficiencies persist over very large areas.
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 storages are still low (see Water section of this Statement).
The role of climate change in rainfall reduction over southern Australia and along the Great Dividing Range is discussed in State of the Climate 2018. Parts of south-west, south-east, 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.
Valuable increases in storage levels in the Murray–Darling Basin
The water storage levels increased in most of the major storages in the Murray–Darling Basin. The total storage reached 55% at the end of August, an increase of 8% since last month and 13% since the same time last year.
Total water storage in the northern Murray–Darling Basin increased by 5.1% this month, but at 25.5% of capacity (1,180 GL) there is a long way to go before the water supply systems are replenished. The largest increase of 14% was seen in the Burrendong storage in the Macquarie Valley, followed by 8% in the Keepit storage in the Namoi Valley, which rose from 18 to 24%. The Keepit storage is now at 24% which is a significant increase from 1% this time last year. Unlike the significant and rapid recovery of the northern Basin storages in 2010 and 2016, the current rate of recovery is slower, and more rainfall is still needed to refill these northern Basin water storages.
The total storage in the southern Basin increased by 8.8% during August to 62.8% (12,815 GL), 13.7% higher than August 2019. The most significant gains were seen in the southern New South Wales storages of Googong, Wyangala, and Burrinjuck; which rose by between 30 and 36% in August. This was the fourth-highest monthly increase for Burrinjuck in the past 10 years. Wyangala and Burrinjuck storages provide valuable irrigation and town water supply to the Lachlan and Murrumbidgee valleys respectively, both of which have been severely impacted by this drought. Lake Hume again rose by 12% this month to reach 61% of capacity. This surpasses the previous three winter filling seasons where there were insufficient inflows to replenish the seasonal drawdown. The filling season in the southern Basin will generally continue until the end of September.
Rivers throughout New South Wales return to average or above average flows
The Lachlan, Murrumbidgee, Castlereagh, Macquarie and Namoi rivers all received valuable inflows in August, increasing river levels to average or above average at most gauge locations.
Many of the southern Basin rivers are running at below average for August but there are still significant flows (>2,500 ML/day) in the Murray, Murrumbidgee, and Lachlan rivers. Flows down the Murray River into South Australia this season have allowed more than 200 GL of water to be released into the Coorong for environmental outcomes.
Minor flows are being maintained down the Lower Darling River with releases from the Menindee Lakes but there are no significant flows in the Darling upstream of Menindee Lakes.
Storage and river levels in south-west Western Australia remain low
The rain in August in south-west Western Australia fell on very dry soils and did not fall far enough inland to produce significant runoff and inflows to the major water storages in the region. The total storage in the 21 major water storages in the South West Coast drainage division is at 43.6% of capacity, an increase of only 2.5% in August. The largest increase resulted from rain on the south coast where the small storage of Quickup increased by 37% to 80% of capacity. However, the larger storages of Wellington and Serpentine only increased by 4% and 1.6% respectively.
The Perth water supply system relies on desalinated water and groundwater extraction to supplement natural inflows to water storages which buffer the supply system against extended dry periods. The dry conditions are more accurately reflected in the Harvey rural supply system south of Perth where water storage levels have been declining since the start of the 2018 spring irrigation season. The 2020 winter filling season has increased the storage in the system by 25,000 ML (8,000 ML in August) but a further 70,000 ML is needed to replenish the drawdown of the past two years.
Above average rainfall for August through much of the interior of Australia, New South Wales, and parts of the south-east coast has resulted in an increased in root-zone soil moisture (in the top 100 cm) across large areas, compared to July.
Soil moisture was above average for August through the interior of the continent, most of the eastern half of New South Wales and far eastern Victoria. Soil moisture was also above average in a narrow strip along the south coast of Western Australia and in south-east Tasmania.
Soils were drier than average for the month across much of the south of Western Australia except right along the south coast; much of south-east South Australia and the Eyre Peninsula, south-western Victoria, north-western Tasmania, much of the Kimberley in Western Australia, the central Northern Territory and the Top End, and parts of central Queensland and the Cape York Peninsula coast.
The influence of very low rainfall over longer timescales is still evident in the 12-month soil moisture for September 2019–August 2020, which was very much below average over large areas, predominantly in the west and south of Western Australia.
Soil moisture increases across most of the Murray–Darling Basin
The above average rainfall in August has led to valuable increases in root-zone soil moisture in the Murray–Darling Basin. Areas in western New South Wales have increased from very much below average in July to above average in August. The soils in the upland areas of the Macquarie and Castlereagh river valleys, near Dubbo, did experience some drying out this month but these areas were very wet at the end of July and remain above average for August. Sustained soil moisture levels during winter have enabled dryland crops to grow through large areas of the Basin in readiness for a spring harvest.
Inland south-west Western Australia remains dry
Coastal rain contributed to significant increases in soil moisture on the coast, but most of southwest Western Australia remained dry in August. Small areas around Albany moved from lowest on record in July to very much above average in August. However, root-zone soil moisture across most of the wheatbelt remained very much below average this month.
Despite monthly fluctuations and localised rain events, the region has been experiencing dry soil conditions since April 2018. The root-zone soil moisture deciles for the 29-month period to August 2020 show a significant portion of the South West Coast drainage division has experienced record-low soil moisture over this period.
- Above average August rainfall through much of the interior of Australia has decreased deficiencies at the 5-month timescale, although deficiencies persist in much of the south-western half of Western Australia and south-east Queensland
- Accumulated rainfall deficits at multi-year timescales are significant in many parts of Australia, and may persist for some time
- Root-zone soil moisture increased across large areas, but remains below average in parts of the southern coast and south-west Australia, and areas of the northern tropics
- Water storages continue to fill in the southern Murray–Darling Basin though levels remain low in the northern Basin
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 15 September 2020, rainfall was recorded in the far south-west Western Australia, south-east South Australia, Victoria, Tasmania, eastern New South Wales, and east coast and south-east inland Queensland. Little or no rainfall was recorded elsewhere.
At the start of the week, a high pressure system in the Tasman Sea extended a firm ridge along the east coast, and moist onshore flow produced showers along parts of Queensland's north tropical, central and south-east coasts
In the first part of the week, a cold front moved away from the south-east, and a broad trough stretched from Central Australia to New South Wales to the west of Tasmania, and tracked eastwards over south-east Australia. The systems tracked eastward and generated widespread light falls over Tasmania, the eastern half of Victoria and south-east New South Wales. Moderate falls were reported in south-west Tasmania.
The surface tough tracked over northern New South Wales and southern Queensland and produced widespread moderate falls in the north-east, and adjacent inland districts in New South Wales. Thunderstorms developed over south-east inland Queensland.
In the west, a cold front brushed the south-west of Western Australia then slipped into the Bight, generating moderate falls in far south-west, and light falls in the far south-east of the state.
During the middle of the week, the cold front stretched across the far south-east of the country, and the associated slow-moving cloudband tracked across south-east Australia. Moderate falls were recorded in south-east South Australia, and in south-west, central and north-eastern Victoria, and Tasmania. At the end of the week, another fast-moving cold front embedded in a westerly flow, tracked across Tasmania and generated moderate falls in that state's west and north-east.
Onshore flow continued along parts of the east coast of Queensland for the rest of the week, with heavier showers affecting the north tropical Queensland coast.
Rainfall totals in excess of 100 mm were recorded in parts of the north tropical and south-east coasts of Queensland; also in an area in north-east New South Wales, including the highest weekly totals of 119 mm at Meldrum (Coolawarrah).
Rainfall totals between 10 mm and 50 mm were recorded in far south-west Western Australia; south-east South Australia; most of Victoria except in the north-west and east, and in western and north-eastern Tasmania. Similar totals were recorded in elevated areas of the Snowy Mountains, and from the central to north coasts, and adjacent inland districts of New South Wales; and across south-east inland Queensland and along the north tropical, central and south-east coasts of that state.
Impact of recent rainfall on deficits
Rainfall deficits over Australia for the 5-month (April–August 2020) period is discussed in the Drought Statement, issued on 8 September 2020.
Rainfall deficit maps are available for this period as well as for standard periods. The map below show the percentage of mean rainfall that has been received for the rainfall deficit period for the 5-month period, extended to the week ending 15 September 2020.
Rainfall for the period 1 April to 15 September 2020
Serious or severe rainfall deficiencies for the 4-month period are in place in Western Australia across most of the southwestern half of the State. Serious rainfall deficiencies are also in place across parts of central southern and southeast Queensland. Other small areas experiencing serious rainfall deficiencies include the southwest of the Alice Springs District in the Northern Territory, and pockets of southwest South Australia.
The rain that fell over the past week eased deficiencies very slightly in areas of south-east inland Queensland.
Inland areas of Western Australia have received less than 40% of average for the period. Remaining areas in Western Australia, South Australia and parts of central Queensland have generally received less than 80% to 60% of their average for the period.
Product code: IDCKGRWAR0