Rainfall deficiencies and water availability
Rainfall deficiencies persist in Queensland
Rainfall for August 2021 was below average for much of southern Australia excluding southern parts of the east coast which saw above average rainfall. Northern parts of Queensland also saw above average rainfall with more southern parts of Queensland seeing average to below average rainfall. This area has seen deficiencies for the period commencing April 2020 persist in areas of Queensland's Capricornia, Wide Bay and Burnett districts, extending west into the Central Highlands District. Rainfall deficiencies established during the drought of 2017–2019 remain over very large parts of the country, and may persist for some time.
Serious rainfall deficiency means an area has received rainfall in the lowest 10% of historical observations for a specified period, compared to all similar periods since 1900 spanning the same calendar months, while severe rainfall deficiency means rainfall totals in the lowest 5% of historical observations.
The Climate Outlook released on 2 September 2021 indicates September to November rainfall is likely to be above median for the eastern two-thirds of Australia, however, some western parts of WA and western Tasmania are likely to see below median rainfall.
17-month rainfall deficiencies
Rainfall for much of the larger quarter of southeast Queensland was average to below average during August 2021, seeing deficiencies persist in the east of the state.
Serious or severe rainfall deficiencies for the period commencing April 2020 persist in the Capricornia and Wide Bay and Burnett districts and extend west into the Central Highlands District in Queensland, and in a pocket of the west of the state near Boulia.
Some isolated areas of deficiencies persist in central regions of Western Australia that missed out on above average winter rain that fell further to the south.
Extended dry conditions over eastern Australia
Multi-year rainfall deficiencies, which originated during the 2017–2019 drought, remain over large parts of the country due to the extremely low rainfall totals experienced over this extended period. The long-term drought and the impact on the Murray–Darling Basin is discussed in Special Climate Statement 70. Seasonal conditions have improved since this point over large areas and water storages across the country, especially in the Murray–Darling Basin have increased.
The 2020–21 La Niña saw improvement of conditions over parts of eastern Australia, although the end of La Niña saw April and May 2021 drier than average across much of mainland Australia, particularly in the south-east. The development of a negative Indian Ocean Dipole during June 2021 led to above average June and July rainfall for much of the coast of the southern mainland and across the south-eastern mainland away from the east coast. Further periods of above average rainfall are needed to continue the recovery, especially in parts of Queensland, parts of South Australia and far west New South Wales, and East Gippsland in Victoria.
Many areas experiencing rainfall deficiencies for periods longer than 24 months have typically experienced below average rainfall between April and October. 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 south-west, south-east, and eastern Australia—including parts of south-east Queensland and southern and eastern New South Wales—have seen substantial declines in cool-season (April to October) rainfall in recent decades.
Root-zone soil moisture (soil moisture in the top 100 cm) was mixed, despite below average August rainfall over much of southern Australia. Soil moisture in more northern parts of South Australia into north-western New South Wales, southwestern Queensland and the Northern Territory is now below average. Soil moisture remained below average for parts of central inland Western Australia. Above average soil moisture was seen in parts of eastern New South Wales inland of the Divide, western Tasmania southern South Australia and south-western Western Australia.
In the northern Murray–Darling Basin soil moisture levels were above average in the east in response to above average winter season rainfall, but below average in the west. Soil moisture was very much above average in many northern Basin catchments including the Namoi, Gwydir and Border Rivers. In the southern Murray–Darling Basin, soil moisture was average or above in most of the areas. Where soils are saturated further rainfall during the spring season may lead to large inflows into water storages.
- Rainfall deficiencies for the period commencing April 2020 persist in Queensland
- Accumulated rainfall deficits at multi-year timescales remain in many parts of Australia
- Water storages continued to fill in the Murray–Darling Basin during the winter season.
- Menindee Lakes water storage levels reached the highest level in eight years.
- Hume dam storage is at its highest level in four years.
- South East and Central Queensland storages remain low.
Storage levels in the Murray–Darling Basin continued to increase significantly
The total water storage (accessible) in the Murray–Darling Basin increased to 82.4% of capacity at the end of the winter filling season, an increase of 6.2% of capacity over the past month. Compared to the same time last year, when the total storage volume was only 56%, water storages are in a significantly better position.
In the northern Basin, the winter filling season has been unusually wet, and the total storage increased by 31% since 1 June, the highest increase during the season (June to August) since January 2010. This was in response to the above average winter rainfall that occurred in the north east of the Murray–Darling Basin. The total storage in the northern Basin increased by 9% to 80.4% of capacity (3 735 GL) at the end of August. This is the highest level since March 2012 and is significantly higher than the same time last year when it was only 25.4%.
The greatest increases during the month were for Jack Taylor Weir (+31%), Burrendong (+17%) and Copeton (+16%) which are all above 80% capacity at the end of August. Other storages, including Pindari, Chaffey, Chinchilla, Keepit and Coolmunda are at or near their full accessible capacities. Despite this, some storages including Split Rock, Windamere and Cooby Creek are less than 50% full.
The total storage in the southern Basin increased by 5.5% to 82.8% (17 097 GL) in August. This is considerably higher than the same time last year when it was only 62.3%. Several storages in the southern Basin are at or near full accessible capacity (Lake Nillahcootie, Googong, Wyangala, Bendora, Corin, Cotter, Lauriston, Malmsbury and Upper Coliban). All three of the very large storages in the southern Basin (Hume, Dartmouth, and Eildon) increased this month. Hume again had the most significant increase of 12.5%, bringing it to 93.1% of capacity, the highest level since November 2016. With the predictions of above median rainfall in spring, there is a high likelihood of Hume dam spilling in coming weeks
The Menindee Lakes system has seen a period of rapid filling since April 2021 to reach 84.6% of accessible capacity in August. Flood waters resulting from above average rainfall in the northern Murray–Darling basin moving down the Darling-Barka River have resulted in the highest water levels in the Lakes since December 2012; significantly higher than the same time last year when it was only 24.8% full.
Further detail on individual Murray–Darling Basin catchments can be found in the Murray–Darling Basin Information Portal.
South East Queensland storages continue to remain low
In South East Queensland, the largest storage, Wivenhoe, decreased in August to reach to 41.7% of capacity, due to the below average rainfall in August. This is lower than the same time last year when it was 45.4% and continues the significant decreases of the past three years.
The water levels of the two large rural systems in South East and Central Queensland, Bundaberg and Nogoa Mackenzie, remained low. The accessible volume of the Bundaberg system dropped further in August to 31.6% of capacity, the lowest level in more than ten years, and significantly lower than the same time last year when it was 51.3%. By the end of August 2021, the storage levels in the Nogoa Mackenzie system dropped to 15.8%, slightly higher than 11.4% storage of same time last year.
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 21 September 2021, rainfall was recorded in south-west Western Australia, in north-western and southern parts of the Northern Territory, far south-east South Australia, southern and north-eastern Victoria, northern and western Tasmania, and eastern New South Wales.
At the start of the week, a low pressure system well off the New South Wales north coast generated moderate falls over the Mid North Coast and Hunter districts. Isolated thunderstorms developed near a surface trough, and produced moderate falls over some parts of the north-west Top End in the Northern Territory.
A cold front tracked across south-west Western Australia, generating showers and thunderstorms, with moderate falls over the west coast of Western Australia, and light falls over the South West Land Division. A cloudband extended from northern Western Australia, through Central Australia to south-east Australia, with showers and thunderstorms producing light to moderate falls in parts of the Kimberley and southern parts of the Northern Territory.
The cold front, a pre-frontal trough and associated cloudband moved over eastern Australia, and generated moderate falls over western Tasmania, north-east Victoria and inland south-eastern New South Wales, while elevated parts of the Snowy Mountains recorded daily falls of 40-50 mm. Light falls were recorded across eastern New South Wales and southern Victoria.
In the last part of the week, another cold front brushed the southern coast of Western Australia, generating light falls in south-west Western Australia. The cold front tracked eastwards across south-east Australia, and generated moderate falls in western Tasmania, southern and north-eastern Victoria, and the Snowy Mountains in New South Wales, with light falls across south-east South Australia and remaining parts of Victoria and Tasmania.
Rainfall totals in excess of 50 mm were recorded in western Tasmania, north-eastern Victoria, and the Snowy Mountains and central coast in New South Wales. Perisher Valley in the Snowy Mountains recorded the highest weekly rainfall total of 132 mm.
Rainfall totals between 10 mm and 50 mm were recorded in south-west Western Australia; north-western and southern parts of the Northern Territory; far south-east South Australia; southern, central and north-east Victoria. Similar totals were recorded in much of eastern New South Wales, and in northern and western Tasmania.
Impact of recent rainfall on deficits
Rainfall deficits over Australia for the 17-month (April 2020–August 2021) period are discussed in the Drought Statement, issued on 6 September 2021.
Rainfall deficit maps are available for the period as well as for standard periods. The maps to the right shows the percentage of mean rainfall that has been received for the period starting April 2020, and extended to the week ending 21 September 2021.
Rainfall for the period 1 April 2020 to 21 September 2021
Serious or severe rainfall deficiencies for the period commencing April 2020 persist in the Capricornia, and Wide Bay and Burnett districts and extend west into the Central Highlands District in Queensland.
Areas around Boulia has received less than 50% of their average for the period, and affected areas in Queensland's Capricornia, and Wide Bay and Burnett districts have generally received between 50% and 80% of their average for the period.
Product code: IDCKGRWAR0