Rainfall deficiencies and water availability
Below average September rainfall for the south-west; short-term deficiencies continue in WA
Rainfall during September 2020 was above average for large areas, but below average in areas of the south-west and south-east of the country, particularly in Gippsland, and also in south-east Queensland and adjacent north-east New South Wales. Rainfall deficiencies at shorter timescales (e.g. the 6 months to September 2020) have increased in parts of Western Australia, although there has been little change at longer multi-year timescales.
Daytime temperatures during September were very much warmer than average for much of the country; the maximum temperature was the second-highest on record for September for Australia as a whole.
The Climate Outlook, issued 1 October, indicates the remainder of 2020 is likely to see above average rainfall across the eastern two thirds of the country. The Bureau will continue to closely watch and report on observed rainfall and seasonal outlooks over coming months.
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 10 to 20% over southern Australia in recent decades. 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.
6-month rainfall deficiencies
Serious or severe rainfall deficiencies for the 6-month period April–September 2020 are in place in Western Australia across most of the southern half of the State, excluding parts of the coast in the Gascoyne, Central West, and South Coastal districts. Deficiencies have increased in severity in Western Australia, with some inland areas showing lowest-on-record rainfall for the period. Serious rainfall deficiencies are also affecting scattered pockets in greater south-east Queensland.
Area-averaged rainfall for the 6-month period was the eleventh-lowest on record for south-west West Australia for April–September, and the second consecutive April–September with rainfall in decile 1, and the fourth consecutive such period in one in decile 1 or 2.
At the slightly shorter 5-month timescale (May–September 2020) deficiencies still persist in northern Tasmania.
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.
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. For example, over half of the country is in severe rainfall deficiency for the 30-month period from April 2018 to September 2020. Regions affected include north-east New South Wales and the south-eastern quarter of Queensland, western New South Wales, north-western and eastern Victoria, much of South Australia, Western Australia, and the Northern Territory.
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 south-eastern Australia and parts of the inland north-west 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.
Major water storage levels remain stable in September
The water storage levels in most of the major storages in the Murray–Darling Basin remained stable in September. The total storage reached 56% at the end of the month, an increase of 1% since last month and 17% since the same time last year.
Total water storage in the northern Murray–Darling Basin remained at 25.9% of capacity (1,200 GL) at the end of September, 18.1% higher than the same time last year. With the exception of Burrendong, at 46% full, all of the larger storages in the northern Basin remain at less than 30%, with Split Rock in the Namoi valley still at only 5%.
The northern Basin does not have a defined 'winter filling season' like the southern Basin. Many of the northern storages are dominated by late spring and summer inflows, providing an opportunity for further filling in 2020. Unlike the significant and rapid recovery of the northern Basin storage levels 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 decreased by 1.3% during September to 61.5% (12,700 GL), 14.7% higher than September 2019. The irrigation season has been slow to start in the southern Basin due to widespread early spring rainfall but releases from many of the major water storages have now commenced.
The only major increase was in Lake Hume where levels increased by 5% this month to reach 65% of capacity. This surpasses the previous three winter filling seasons where there were insufficient inflows to replenish the seasonal drawdown.
Inflow to water storages in south-west Western Australia
The rain on the coastal regions of south-west Western Australia fell on already wet soils and was enough to produce runoff into the local major water storages. The total storage in the 21 major water storages in the region is at 47.6% of capacity, an increase of almost 5% during September. The small southern storages of Quickup and Glen Mervyn both increased by 20% and the largest storage in the region, Wellington, increased by 7.7 %.
Compared to last month, root-zone soil moisture (in the top 100 cm) has decreased across much of the south of Western Australia, and parts of eastern Victoria and eastern New South Wales; but has increased in the Top End and northern Kimberley.
Soils were drier than average for September across much of the south of Western Australia; coastal south-east South Australia and the Eyre Peninsula; parts of Victoria from the south-west to eastern Mallee, and from South Gippsland to the north-east; parts of the Kimberley in Western Australia, the central Northern Territory, and eastern Top End, and parts of central Queensland and Cape York Peninsula.
Soil moisture was above average for the month through much of New South Wales, pastoral areas of South Australia, and the western half of Queensland. Soil moisture was also above average in some parts of the eastern Interior District in Western Australia, the northern coastal Kimberley, and western Top End, as well as some areas elsewhere in the northern half of the Northern Territory and along the western and eastern borders of the Territory.
The influence of very low rainfall over longer timescales is still evident in the 12-month soil moisture for October 2019–September 2020, which was very much below average over large areas, predominantly in the west and south of Western Australia.
Sustained above average soil moisture through the central Murray–Darling Basin
September was the second consecutive month of average to above average rainfall across most of the Murray–Darling Basin. This steady rainfall has maintained root-zone soil moisture levels at above average throughout large areas of the central Basin. Rain in western New South Wales in the second half of the month increased soil moisture to very much above average and resulted in local surface runoff and flows in the Darling River around Wilcannia. Localised storms resulted in flooding in areas such as Broken Hill but for the most part the rain was welcome.
The soils in the upland areas of the Lachlan and Murrumbidgee river valleys did see some drying out this month but these areas were very wet at the end of August and remain above average for September. The sustained soil moisture levels during winter and at the start of spring have enabled dryland crops to be established and maintained throughout large areas of the Basin. These crops will be harvested in spring and early summer and would benefit from some dry conditions prior to harvest.
Inland south-west Western Australia remains dry
Near average rainfall and above average temperatures has reduced soil moisture stores throughout inland south-west Western Australia. The soils remain very much drier than average throughout the wheatbelt and up into the northern agricultural region. These regions rely on dryland agriculture with the primary growing season from May to October. Despite the soil being dry, the near average rain in August and September has been sufficient to sustain the winter growing season and produce grain crops in the region.
Despite a couple of months of near average rainfall and localised rain events, the region has been experiencing dry soil conditions since April 2018. The root-zone soil moisture deciles for the 21-month period to September 2020 show a significant portion of the region has experienced record-low soil moisture over this period.
- September rainfall below average rainfall in areas of the south-west and south-east of the country, and also in south-east Queensland
- Rainfall deficiencies continue at the 6-month timescale in much of the south-western half of Western Australia
- Accumulated rainfall deficits at multi-year timescales are significant in many parts of Australia, and may persist for some time
- Root-zone soil moisture decreased across much of the south of Western Australia, and parts of eastern Victoria and eastern New South Wales
- Water storages levels have decreased in the southern Murray–Darling Basin but remain stable in the northern Basin
- Major water storages in south-west Western Australia received some inflows, but inland soils remain very dry
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 27 October 2020, rainfall was recorded in the Kimberley and along the southern coast of Western Australia; much of the Northern Territory except in the south-west; South Australia except in the north-west; most of Queensland, New South Wales, Victoria and Tasmania.
In the first part of the week, broad areas of low pressure extended across western, central and eastern parts of the continent, with thunderstorms developing over the south and north of Western Australia, north-western and southern parts of the Northern Territory, central to south-east Queensland and north-east New South Wales. A low pressure centre deepened along a trough over south-east Western Australia, and moved into western South Australia, producing a cloud band and moderate falls in south-east Western Australia, southern and eastern parts of South Australia, and triggered storms through parts of the Northern Territory and western Queensland. Showers and thunderstorms also developed near a trough along the New South Wales coast, with moderate falls reported in south-east Queensland, and north-eastern New South Wales.
By the middle of the week, the low pressure system and multiple surface troughs had moved into western New South Wales. Extensive areas of thunderstorms and showers developed across the Northern Agricultural District in South Australia; western, southern and along the Tablelands in New South Wales; southern central to north-eastern Victoria, and parts of northern Tasmania. An extensive cloud band with embedded thunderstorms also affected western, the northern and central interior, and south-east inland areas of Queensland.
In the last part of the week, the low pressure system tracked across northern New South Wales, with surface troughs extending north into Queensland, and across the base of the Top End in the Northern Territory. Thunderstorms produced moderate falls in areas of Arnhem Land and the Gulf Country, and the Cape York Peninsula. Thunderstorms also affected areas from the northern tropics, Central Highlands to south-east Queensland, much of central to eastern New South Wales, and the eastern half of Victoria. The low pressure system moved off the north-east New South Wales coast and the trough deepened over the east coast of Queensland and New South Wales. Thunderstorms developed over central to south-east Queensland, east coast New South Wales and eastern Victoria. Severe thunderstorms produced large hail, heavy rainfall and damaging winds over south-east Queensland, and areas around the Mid North Coast and Hunter districts in New South Wales reported isolated heavier falls.
At the end of the week, thunderstorms with widespread moderate falls were reported in the northern half of the Northern Territory. Thunderstorms also produced moderate falls along parts of the north tropical to central coasts of Queensland, and along the central to south-east coasts of New South Wales, with some isolated heavier falls in the Mid North Coast of that state.
Rainfall totals exceeding 200 mm were recorded in parts of the Mid North Coast and Hunter Districts in New South Wales, including the highest weekly total of 246 mm at Wyong (Mount Elliott) in the Hunter District in New South Wales. Falls in excess of 250 mm were reported from some sites with non-standard Bureau equipment.
Rainfall totals exceeding 50 mm were recorded in isolated areas of Gregory District and parts of the western Gulf Country in the Northern Territory and parts of the northern interior, Central Highlands and Darling Downs districts in Queensland. Similar totals were recorded in the Tablelands, Mid North Coast to south-east of New South Wales; in north-east and East Gippsland in Victoria; and in a small area of the Flinders District in South Australia.
Rainfall totals between 10 mm and 50 mm were recorded in the Kimberley and along the south coast of Western Australia; southern and eastern parts of South Australia; most of the northern half and southern parts of the Northern Territory; large parts of Queensland and New South Wales, most of Victoria, and northern and eastern Tasmania.
Impact of recent rainfall on deficits
Rainfall deficits over Australia for the 6-month (April–September 2020) period is discussed in the Drought Statement, which was issued on 7 October 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 6-month period, extended to the week ending 27 October 2020.
Rainfall for the period 1 April to 27 October 2020
Serious or severe rainfall deficiencies for the 6-month period April–September 2020 are in place in Western Australia across most of the southern half of the State except for parts of the coast in the Gascoyne, Central West, and South Coastal districts. Deficiencies have increased in severity in Western Australia, with some inland areas showing lowest-on-record rainfall for the period. Serious rainfall deficiencies are also affecting scattered pockets in south-east Queensland.
Rainfall in the last week has eased deficiencies very slightly in parts of south-east Queensland and south-east Western Australia, but had little impact elsewhere over this time period.
Inland areas of Western Australia have generally received less than 20% their average for the period, while remaining areas in Western Australia and areas in south-east Queensland and have generally received less than 80 % to 40% of their average for the period.
Product code: IDCKGRWAR0