Rainfall deficiencies and water availability
Little change to rainfall deficiencies in Queensland; April rainfall low for south-east Australia
Rainfall for April 2021 was below average for most of mainland Australia, and for New South Wales it was the equal-eighth-driest April on record and for South Australia it was the seventh-driest April on record. Rainfall for the month was above average for Queensland's Cape York Peninsula and adjacent northern Queensland, and around most of the west and north-west coast of Western Australia. For the areas of Queensland's Capricornia and Wide Bay and Burnett districts, where serious or severe rainfall deficiencies exist, April rainfall was mostly close to average resulting in little change in existing deficiencies.
Deficiencies for the periods January 2017 to present and January 2018 to present still exist over very large parts of the country. More rainfall is needed over an extended period to continue the recovery from the extended dry conditions of 2017 to 2019.
The Climate Outlook, issued 6 May 2021, indicates that June to August rainfall is likely to be above average for much of the eastern two-thirds of mainland Australia. Areas in the west, north and far south-east of Australia have roughly equal chances of above or below average rainfall. Winter is generally a drier time of the year for northern Australia.
At the 3-month timescale, February–April 2021 rainfall was below average for large areas of western Victoria, south-west New South Wales, and south-east South Australia although, as mentioned, these months typically see low rainfall totals in areas such as Victoria's Mallee and South Australia's Mid North.
The Bureau will continue to monitor rainfall over the coming month and season, particularly in parts of south-east Australia which typically see their transition from the climatologically driest part of the year during January to April to wetter conditions in the cool season, from May.
13-month rainfall deficiencies
Serious or severe rainfall deficiencies for the 13-month period April 2020 to April 2021 persist in the Capricornia and Wide Bay and Burnett districts in Queensland. While areas further north largely received above average rainfall for the month, for areas of Queensland with serious or severe rainfall deficiencies, rainfall was mostly close to average. Compared to the previous Drought Statement, deficiencies have increased in the south of the region, extend further inland in the north, and have lessened around the south-west of the Capricornia District.
Extended dry conditions over eastern Australia
Australia has experienced a prolonged period of below average rainfall spanning several years. Persistent, widespread, above average rainfall is needed to further lift areas out of deficiency at the multi-year timescales and provide relief from the impacts of this long period of low rainfall, such as by further recharging water storages.
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 and south coasts 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. Rainfall in 2020 and in early 2021 saw improvement across many areas, though April was drier than average across much of mainland Australia and particularly the south-east.
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 rainfall in recent decades.
Compared to last month, root-zone soil moisture (in the top 100 cm) has decreased for much of southern mainland Australia.
Soil moisture was below average for western Victoria, south-west New South Wales, and south-east South Australia, and for a large area stretching from south-east Western Australia into the interior of that state.
Soils were wetter than average for the month across much of New South Wales except in the south-west, southern parts of Queensland, the northern parts of South Australia, the south and west of the Northern Territory, and the Kimberley and parts of the west coast of Western Australia.
The influence of very low rainfall over longer timescales is still evident in the 19-month soil moisture for October 2019 to April 2021, which was very much below average over large areas, predominantly in the southern half of Western Australia, but also in parts of Queensland extending from the east coast through central and northern Queensland to the Northern Territory border, and in western Victoria.
- Rainfall deficiencies in Queensland similar to those for the period to March 2021
- Accumulated rainfall deficits at multi-year timescales remain significant in many parts of Australia, and may persist for some time
- Water storage levels in the northern Murray–Darling Basin continued to increase during April
- Northern Australia water storage levels remained above 80% of accessible capacity during April
- South East Queensland water storage levels remain low
- Groundwater levels have improved in the Murray–Darling Basin and northern Australia
Storage levels in the northern Murray–Darling Basin continued to increase
In response to heavy rainfall that fell over the northern Murray–Darling Basin during the second half of March, soil moisture levels remain above average to very much above average in April. This has brought great relief to the drought affected areas in the New South Wales Border Rivers, Namoi and Gwydir catchments. In contrast, soil moisture levels were below average to very much below average in the southern Murray–Darling Basin due to the below average to very much below average rainfall in April.
The total water storage in the Murray–Darling Basin decreased slightly in April. Total storage was 56% of capacity at the end of the month, a decrease of 1% of capacity since the last month. Compared to the same time last year when the total storage volume was only 35%, the water storages are in a significantly better position.
Total water storage in the northern Basin increased by 1.5% to 48.9% of capacity (2, 271 GL) at the end of April, which is much higher than the same time last year when it was only 16.7%. The greatest increase was for Chinchilla which reached 99% of accessible capacity. Coolmunda and Lake Kajarabie (Beardmore Dam) remained close to their full accessible capacities at the end of April. Other storages observing increases in volume are Glenlyon (+5%) and Keepit (+5%). Despite the general increase, some storages like Split Rock, Windamere, Leslie and Cooby Creek were less than 35% full and other storage such as Copeton and Pindari are less than 50%.
Although above to very much above average rainfall fell across the New South Wales part of the southern Basin in late March, the total storage in the southern Basin (where the major storages are located) dropped by 1.2% to 57.6% of capacity at the end of April. This is, however, significantly higher than the storage situation at the same time last year when it was only 39.8%. The highest percentage decrease in the storage volumes in April were for Lake Buffalo (−9%), Upper Coliban (−9%), Burrinjuck (−8%), Hume (−6%), Lake Nillahcootie (−6%) and Lake Eildon (−4%). However, despite the overall decline, some individual storages like Bendora, Googong, Corin and Cotter, were close to their full capacities.
Floodwaters from record rainfall in the northern Murray–Darling Basin at the end of March have started to reach the Menindee Lakes and the storage volume has increased by 13.5% to 30.7% of capacity at the end of April. Significant increases in storage volumes were also observed in Lake Wetherell (+40%) and Lake Pamamaroo (+28%).
Further detail on individual Murray–Darling Basin catchments can be found in the fortnightly Water Reporting Summaries for MDB Catchments.
Northern Australia water storage levels recovered during the wet season and remained above 80% of accessible capacity in April
The northern Australian monsoon season commenced in December and officially finished in April bringing above average rainfall in northern parts of Northern Territory and northeastern Western Australia. In response, the volume of water in two of the major water storages in northern Australia has increased significantly during this wet season.
Water levels in Lake Argyle, the largest water supply storage in Australia (10,400 GL) had been decreasing since September 2017 as the past three wet seasons had not delivered significant inflows to the storage. Lake Argyle was at 25% of accessible capacity by the end of November 2020, the lowest level in almost 30 years. This year's monsoon brought relief and the Lake Argyle's storage volume reached 82.1% of accessible capacity by the end of March. Total water storage in the Lake Argyle decreased by 1.6% to 80.5% of capacity (8,398 GL) at the end of April, but is still 37.1% of capacity higher than the same time last year.
The normal filling and spilling of the Darwin River storage did not occur for the past two wet seasons (2018–19 and 2019–20). The accessible volume dropped to 50 per cent of capacity in December 2020, the lowest level in more than 10 years. Due to above average rainfall during the wet season the storage volume reached 94.3% of capacity at the end of March and remains at 93.5% at the end of April. This is significantly higher than the storage situation same time last year when it was only 72%.
South East Queensland storages remain low
In South East Queensland, the largest storage, Wivenhoe, which has decreased significantly in the past three years, increased by 4.4% in April to reach to 41.3% of capacity, but is significantly lower than the same time last year when it was 51.2%.
Groundwater levels are showing signs of recovery in the Murray–Darling Basin and have recovered in northern Australia
The drought in the Murray–Darling Basin (MDB) since 2017 resulted in widespread declines in groundwater levels in the MDB due to increased pumping and reduced or no recharge. In 2020–21 groundwater levels started to show signs of the usual annual recovery, although the response is still mixed. However, the full impact of the floods on groundwater levels the northern part of the Basin (e.g. Lower Namoi bore) will not be fully observed for a while due to the delayed response of groundwater.
In contrast, groundwater levels in the more responsive limestone aquifers in northern Australia have recovered due to the increased recharge during this wet season. Groundwater levels in the Tindall Limestone aquifer near Katherine peaked in late-February 2021 (increased by 5 metres) and again in March 2021 following very high rainfall during those months, before starting to drop in April. Prior to the 2020–21 wet season, groundwater levels were the lowest in more than 20 years as almost no recharge occurred during the 2018–19 and 2019–20 wet seasons due to the low rainfall received.
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 11 May 2021, rainfall was recorded in western parts of Western Australia, agricultural districts and parts of eastern and central South Australia, Victoria, Tasmania, southern and eastern New South Wales, and south-east and southern inland Queensland.
At the start of the week, a deep trough was located over the central Pilbara, and moisture streamed in from the Indian Ocean to generate a large cloudband over much of Western Australia. Isolated thunderstorm occurred along the coast of Western Australia from the Pilbara though to the South West District, and widespread moderate falls were recorded across the west of Western Australia.
In the east, a cold front and low pressure system located over southern New South Wales interacted with a surface trough extending along the south-east Queensland and New South Wales coasts. The systems generated widespread moderate to locally heavy falls in south-east Queensland, along the east coast of New South Wales, and eastern Victoria. The low pressure system and trough moved off the coast of New South Wales, but continued to generate moderate to heavy falls across the central to south-east coast of that state until the middle of the week.
In the middle of the week, surface troughs produced light falls over the south-west coast of Western Australia. The troughs moved eastwards, and brought light falls to the interior of Western Australia and across agricultural and central and eastern districts in South Australia, then western New South Wales and north-west Victoria. A series of cold front tracked across the Southern Ocean, and across western Tasmania, generating mainly light falls in the west of that state.
At the end of the week, isolated thunderstorms developed near a pre-frontal surface trough t over north-eastern New South Wales and south-east Queensland. A vigorous southerly flow associated with the passage of a complex low and cold fronts brought widespread light falls to the south-east, with moderate falls in southern, central and north-eastern Victoria, western Tasmania, and elevated areas of the Snowy Mountains in New South Wales. Light falls were also reported along the southern coastline of mainland Australia.
Rainfall totals in excess of 200 mm were recorded along the South Coast District of New South Wales, including the highest weekly rainfall total of 426 mm at Braidwood.
Rainfall totals in excess of 100 mm were recorded in small areas of the Pilbara coast in Western Australia, and in the Illawarra and South Coast districts of New South Wales.
Rainfall totals between 50 mm and 100 mm were recorded in the western Pilbara and an area of south-west Western Australia, a pocket in western Tasmania, areas of eastern Victoria, and the South Coast District in New South Wales.
Rainfall totals between 10 mm and 50 mm were recorded in the west of Western Australia, in agricultural and parts of eastern and central South Australia, and northern and western Tasmania. Similar totals were recorded in southern, central, eastern and north-eastern Victoria, eastern New South Wales, and south-east and southern inland parts of Queensland.
Impact of recent rainfall on deficits
Rainfall deficits over Australia for the 13-month (April 2020–April 2021) period are discussed in the Drought Statement, issued on 6 May 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 11 May 2021.
Rainfall for the period 1 April 2020 to 11 May 2021
Serious or severe rainfall deficiencies for the 13-month period April 2020 to April 2021 remain in the Capricornia and Wide Bay and Burnett districts in Queensland, and in an area of the Goldfields District in Western Australia.
Rainfall in the past week has had little effect on existing rainfall deficiencies.
Affected areas in the Goldfields in Western Australia have received less than 50% of their average for the period. Queensland's Capricornia and Wide Bay and Burnett districts have generally received less than 70% of their average for the period.
Product code: IDCKGRWAR0