Rainfall deficiencies and water availability
Little change to deficiencies in southern coastal Queensland
Rainfall for September 2021 was below average for the southern half of Western Australia, much of South Australia, much of the east coast between the Central Tablelands in New South Wales and the Wide Bay and Burnett District in Queensland, and for north-east Tasmania. For much of coastal South Australia rainfall for the month was very much below average (amongst the lowest 10% of historical observations for the month).
Areas of Queensland's Capricornia, Wide Bay and Burnett districts, extending west into the Central Highlands District have been experiencing deficiencies for the period commencing April 2020. Average or below average rainfall over these areas during September has seen little change in these deficiencies.
Elsewhere, rainfall deficiencies established during the drought of 2017–2019 remain over very large parts of the country, also with little change, 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 30 September 2021 indicates October to December rainfall is likely to be above median for most areas of Australia, with a greater than 80% chance of above median rainfall over much of the south-east mainland. However, western Tasmania is likely to see below median rainfall.
18-month rainfall deficiencies
Rainfall for south-eastern Queensland and the Wide Bay and Burnett District was below average during September 2021, and generally near average for the remainder of the south-eastern quarter of Queensland. As a result there has been little change to existing rainfall deficiencies.
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 accumulated rainfall totals experienced over this extended period. Over the past two years, seasonal conditions have improved over large areas, and water storages have increased across much of the country, especially in the Murray–Darling Basin.
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 weak 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, with September also wetter than average for much of inland New South Wales and eastern Victoria.
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) for September 2021 was generally above average across the north of Australia, and below average for parts of southern to central Queensland, much of the southern two thirds of Western Australia, and most of South Australia.
Soil moisture was above average in eastern Victoria following a very wet September, and also above average in parts of eastern New South Wales inland of the Divide, around the border of New South Wales–South Australia–Queensland, and in parts of western Tasmania, and the South Coast to Great Southern districts of Western Australia.
The northern Murray–Darling Basin soil moisture levels were mostly average in the east in response to the above average winter season rainfall, but below average in the west. Soil moisture was very much above average in some parts of the Namoi and Gwydir catchments. In the southern Murray–Darling Basin, soil moisture was average in most areas and above average in some areas in the east. 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
- 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 continued to increase and reached 86.1% of capacity at the beginning of the spring season; an increase of 3.7% of capacity over the last month. Compared to the same time last year, when the total storage volume was only 57.6%, the water storages are in a significantly better position.
In the New South Wales part of the northern Basin, the winter filling season was relatively wet. However, that filling rate has slowed down during the first month of spring but continued. The total storage in the northern Basin increased by 1.4% to 81.8% of capacity (3 800 GL) at the end of September. This is the highest level since March 2012 and is significantly higher than the same time last year when it was only 26%.
In the northern Basin, the biggest change in storage during the month were for Chinchilla Weir (−12%), Lake Fyans (−9.5%), and Jack Taylor Weir (−9.5%). In the northern Basin, some storages (Pindari, Chaffey, Keepit, and Coolmunda) are at or near their full accessible capacities. Despite this, other storages including Split Rock, Windamere, and Cooby Creek are less than 50% full.
The total storage in the southern Basin increased by 4.3% to 87.1% (20 662 GL) in September. This is considerably higher than the same time last year when it was only 64.6%. 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) continued to increase this month. Hume has increased by a further 2.8%, bringing it to 96% of capacity, the highest level since November 2016. In September, the dam was operated in controlled release mode to create airspace and prevent the dam from spilling. With predictions of above median rainfall in spring, there is a possibility of Hume dam spilling in coming weeks.
The Menindee Lakes system has seen a period of rapid filling since April 2021 to reach 113% of accessible capacity (spilling) in September. 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 27.2% 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 September, falling to 40.5% of capacity, due to below average rainfall during the month. This is lower than the same time last year when it was 43. 9% 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 September to 29.8% of capacity, the lowest level in more than ten years, and significantly lower than the same time last year when it was 49.2%. By the end of September 2021, the storage levels in the Nogoa Mackenzie system dropped to 14.5%, slightly higher than 10.3% of storage at the 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 19 October 2021, rainfall was recorded along the west coast of Western Australia, in the north of the Northern Territory, eastern Queensland, and across south-eastern Australia including Tasmania.
At the start of the week, a surface trough extended from north-west to south-east Queensland, and combined with moist onshore flow to produce thunderstorms and moderate falls across south-east Queensland and the north-eastern quarter of New South Wales. A cold front was located over eastern South Australia, with an associated low pressure system in the Great Australian Bight. The system moved eastwards into central New South Wales and Victoria, and generated a cloud band with isolated thunderstorms. Moderate falls were recorded in southern South Australia, Victoria, northern Tasmania, eastern New South Wales and south-east Queensland. Thunderstorms developed in the Top End of the Northern Territory and parts of the Gulf Country, along a surface trough across northern Australia.
The low pressure system moved over eastern South Australia, with an associated pair of cold fronts located over western and eastern New South Wales. Secondary lows were also in the western and eastern Bass Strait. The complex low pressure system brought severe storms, damaging to destructive winds, and widespread rain with moderate to locally heavy falls across the east and south-east, including Tasmania. A tornado was confirmed at Armidale in New South Wales on the 14th. A surface trough also extended from south-east to north-west Queensland and across the Top End, with showers and thunderstorms generating moderate falls in north-east and south-east Queensland and the north-east Top End.
Isolated showers brought light falls to parts of the north and south of the country in the middle of the week.
At the end of the week, a surface and upper-level trough produced thunderstorms from the Capricornia to south-east coasts, and adjacent inland districts, and in north-east New South Wales, with giant hail and heavy rainfall associated with the storms. A weak cold front crossed Tasmania and a pre-frontal trough tracked through Victoria, generating moderate falls in north-east Tasmania and East Gippsland in Victoria. In the west, a cold front brought moderate falls along the west coast between Shark Bay and Bunbury in Western Australia. Isolated thunderstorms developed in the Top End.
Rainfall totals in excess of 100 mm were recorded in small areas of south-east Queensland, north-east New South Wales, and north-east Tasmania. The highest weekly total was 241 mm at Gray (Dalmayne Road) in Tasmania.
Rainfall totals in excess of 50 mm were recorded northern and southern Tasmania, parts of southern and eastern Victoria, south-east and north-east New South Wales, and south-east Queensland.
Rainfall totals between 10 mm and 50 mm were recorded along the west coast of Western Australia, southern South Australia, most of Victoria except the north-west corner, Tasmania, the south and eastern half of New South Wales, parts of eastern Queensland, and in the north of the Northern Territory.
Impact of recent rainfall on deficits
Rainfall deficits over Australia for the 18-month (April 2020–September 2021) period are discussed in the Drought Statement, which issued on 6 October 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 19 October 2021.
Rainfall for the period 1 April 2020 to 19 October 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, 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.
Rainfall in the past week eased deficiencies slightly in small areas of the Wide Bay and Burnett District in Queensland, but had little impact on deficiencies elsewhere.
Areas around Boulia have 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