Short-term rainfall deficiencies strengthen in parts of southern Australia

April rainfall was below average for western Tasmania, coastal south-eastern South Australia, south-western Victoria, and a large area of Central Australia spanning the south-west of the Northern Territory and interior of Western Australia. Those regions are experiencing high levels of evaporative stress, resulting in occurrence of flash drought.

Despite very heavy rainfall along parts of the east coast in recent months, rainfall has been average or below average for large areas of the west-facing coasts of south-eastern Australia. As a result, serious or severe rainfall deficiencies are affecting western Tasmania and parts of coastal southern Australia.

While La Niña typically leads to above average summer rainfall for much of eastern Australia, there is no strong signal south of the Dividing Range in Victoria. Below average rainfall in western Victoria, western Tasmania, and parts of south-east South Australia in recent months has been influenced by persistent anti-cyclones ("blocking highs") in the Great Australian Bight and southern Tasman Sea, which have diverted cold fronts and moist tropical air away from the region. A persistent positive phase of the Southern Annular Mode (SAM), and La Niña in the tropical Pacific have also contributed to this. The Bureau's State of the Climate 2020 reported that April to October rainfall for south-eastern Australia has declined around 12% since 2000, compared to 1900–1999 rainfall. This is due to a shift in weather patterns as a known response to global climate change.

In the tropical north, there has been a reduced number of active Madden Julian Oscillation (MJO) events (i.e. monsoon bursts), resulting in dry conditions over the past 3 months. A persistent pattern of MJO events stalling in the Indian Ocean and/or weakening rapidly as they approach Australia may have been influences by very warm waters in the Indian Ocean.

The Climate Outlook released on 5 May 2022 indicates rainfall for June to August is likely to be above median for most of Australia. However, south-western Australia, the south-east coast, and southern Tasmania which have roughly equal chances of above or below median rainfall (i.e. the chance of exceeding median rainfall is close to 50%).

Multi-year rainfall deficiencies, which originated during the 2017–2019 drought, continue to affect parts of the country. The accumulated rainfall anomalies at these longer timescales will persist for some areas for some time yet. However, for recent seasons, conditions have improved over large areas, and water storages have increased across much of the country.

5-month rainfall deficiencies

April rainfall was below average for western Tasmania, coastal south-eastern South Australia, south-western Victoria, and a large area of Central Australia spanning the south-west of the Northern Territory and interior of Western Australia. April rainfall was in the lowest 10% of historical observations for the month (decile 10) for western Tasmania and parts of coastal south-east South Australia and south-west Victoria.

5-month rainfall deficiencies are affecting western Tasmania and parts of coastal southern Australia. Compared to the 4-month period ending March 2022 the strength of these deficiencies has increased. For western Tasmania, extending into the Central Plateau and parts of the south, rainfall for December 2021 to April 2022 has been the lowest on record (compared to observations since 1900).

Serious and severe rainfall deficiencies for the period December 2021 to April 2022, compared to all years since national records began in 1900, are in place across western to central and much of southern Tasmania, coastal south-east South Australia, the south-west coast of Victoria and in an area to the east of Melbourne.

Serious or severe rainfall deficiencies at the 5-month timescale are also observed in part of Queensland's Central Coast and Capricornia districts (but have decreased in spatial extent compared to last month); in the Northern Territory across the base of the Top End and in small pockets of the central Top End; and in some pockets of northern Queensland near Townsville and Cloncurry. The latter part of the northern wet season has been particularly dry for much of northern Australia, with rainfall for the 3 months February to April 2022 in the lowest 10% of historical observations for the month (decile 10) for much of the northern half of the Northern Territory.

The evaporative stress index (ESI) is an indicator of rapid change (on the scale of weeks) into drier conditions leading to vegetation moisture stress. Sometimes called 'flash drought', this index can highlight areas that may be experiencing the impacts of a rapid intensification of drought conditions. High levels of evaporative stress are evident across large parts of the northern half of the Northern Territory; parts of northern Queensland across the base and into the Central Coast region; much of western Tasmania, and parts of far south-east South Australia and south-western Victoria. For more information on the Flash Drought index see published scientific papers.

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Soil moisture

Root-zone soil moisture (soil moisture in the top 100 cm) for April 2022 was below average for western to central Tasmania, south-west and central southern Victoria, and coastal south-east South Australia. Soil moisture was also below average for much of the northern tropics: extending along Queensland's coast from around Rockhampton north to around Cairns, across the southern half of the Cape York Peninsula; much of the Northern Territory away from the western Top End, south-west, and parts of the south-east of the Territory; and for part of the south-east of the Kimberley. Lastly, soil moisture was below average for part of the coastal Pilbara, and an area of inland south-east Western Australia.

Soil moisture was above average for most of the west of Western Australia, extending into the south coast, and for parts of the eastern Interior; across eastern Victoria, eastern to central New South Wales, and south-eastern to central southern Queensland; parts of western New South Wales, north-western Victoria, and parts of north-east South Australia and part of the northern Eyre Peninsula; and pockets of far northern Australia in the north-west coastal Kimberley and adjacent parts of the south-western Top End, and the tip of Cape York Peninsula.

Compared to last month, soil moisture has generally increased across the west of Western Australia, decreased across the Eyre Peninsula and south-eastern South Australia, western and central southern Victoria, and Tasmania.

Saturated soil conditions across eastern Australia have been a significant contributor to the severity of flooding in eastern New South Wales, south-eastern Queensland, and eastern Victoria in recent months. Further rainfall onto saturated soils may result in large inflows into water storages. Wet soils, high streamflows, and full storages increase the risk of flooding.

  • April rainfall was below average for western Tasmania, coastal south-eastern South Australia, south-western Victoria, and a large area of Central Australia spanning the south-west of the Northern Territory and interior of Western Australia
  • Serious rainfall deficiencies (totals in the lowest 10% of historical observations since 1900) are affecting parts of southern Australia for the period starting December 2021
  • Serious rainfall deficiencies are also observed in the Northern Territory across the base of the Top End and in part of Queensland's Central Coast and Capricornia districts
  • Major flooding occurred in inland southern Queensland and inland Northern New South Wales, with widespread flooding in coastal regions of New South Wales during April
  • Minor to moderate flooding occurred around the Daintree region in coastal tropical Queensland
  • High streamflows were recorded in the South-East Coast and Murray–Darling Basin
  • At the end of April, Australia's total storage volume was at 69% of full capacity
  • Urban storages reached above 80% of capacity in all capital cities except Adelaide and Perth
  • Many storages in the Murray–Darling Basin are at full capacity
  • Storages in Northern Australia increased during the monsoon season and reached above 75% of capacity
  • Low storage conditions continue in some parts of central Queensland and the Wimmera–Mallee region of the Murray–Darling Basin

Significant flooding in parts of eastern Australia

Persistent and intense rainfall that started during the last week of March and continued through the first week of April in northern, central and southern coastal areas of New South Wales, including Sydney. Widespread flash flooding and major riverine flooding resulted, particularly in the Hawkesbury–Nepean Valley.

April began with major flooding across inland southern Queensland, which continued throughout the month. Major flooding occurred for several inland river systems in northern New South Wales as water flowed downstream from Queensland.

In late April, a low-pressure trough moving northwards along the Tropical North Queensland coast brought heavy rain to coastal areas of tropical Queensland and caused minor to moderate flooding around the Daintree region.

High streamflow in the South East Coast and Murray–Darling Basin

In April, average to very much above average rainfall over the eastern half of Australia and some parts of the Pilbara in the west was reflected in the streamflow conditions of these regions. In the South East Coast and in the southern part of the North East Coast, streamflow gauges (with records at least from 1980) recorded very much above average streamflow. In many Victorian sites in the South East Coast, streamflows were the highest on record. In the Murray–Darling Basin, half of the streamflow gauges recorded very much above average or record flow. Streamflows were mostly below average in Tasmania, especially in the west of the state, and also in western Victoria and the South West Coast.

Streamflow decile rankings across Australia
Streamflow decile rankings across Australia

Overall high storage levels across the country and capital cities

By the end of April, the total water storage volume in Australia reached 69% of full capacity; slightly lower than the previous month. Despite most of the major storage levels being high, there are individual pockets of low storages volumes particularly in western Victoria, central Queensland, western Tasmania and some urban surface water storages for Adelaide and Perth.

Major storage levels across Australia
Major storage levels across Australia

Storage volumes were above 80% full capacity for all capital cities except Adelaide and Perth.

Storage levels for capital cities
Capital city storage levels

Rainfall for April for coastal south-east South Australia was below average, contributing to reduced run-off and inflows in some of Adelaide's surface water storages. In addition to surface water storages, Adelaide's water supply need is met by water transfers from the River Murray, desalinated water, and groundwater.

Perth's surface water storages were just below half capacity at the end of April (up from 38.6% at the same time the previous year). However, with the long-term decline of surface water inflows into storages, the city's water supply is generally more reliant on desalination and groundwater sources than surface water. Perth's water supply strategy involves 'banking' of groundwater and desalinated water in its surface water storages during low demand periods to buffer peak supply period requirements.

Some central Queensland water storages remain low

Despite above average rainfall along the north-east coast of the state, central Queensland received mostly average to below average rainfall during April, resulting in reduced storage volumes. In the Bundaberg system, the storage volume decreased slightly compared to the previous month, although it is higher than the same time last year. In the Nogoa Mackenzie system, storage levels continued to decline during April (by 1%) and the volume reached an even lower level than the same time last year.

Northern Australia water storage levels are above 75% of accessible capacity

Despite only receiving average rainfall during the northern Australian wet season (October–April), the volume of water in two of the major water storages in northern Australia increased. This is mainly due to the monsoon flow and associated tropical low which developed into tropical cyclone Anika in the Timor Sea producing good inflows to the storages on top of relatively better conditions in the preceding winter season. In April, the storage volume in Lake Argyle decreased by 2.6% and the Darwin River storage remained at its full capacity, similar to the previous month.

Total storage volume in the Murray–Darling Basin remains high

During April, much of the Murray–Darling Basin received average to above average rainfall. At the end of April, the total water storage in the Murray–Darling Basin decreased slightly by 1% from the previous month and fell to 85% of capacity. Compared to the same time last year, when the total storage volume was only 56%, the water storages are generally in a much better position.

The total storage in the northern Basin was 93% of capacity at the end of April, similar to the previous month but significantly higher than the same time last year when it was only half full.

The total storage in the southern Basin decreased slightly to 84% of capacity in April. This is still considerably higher than the same time last year when it was only 58%. Most of the storages in the southern Basin are at or near full capacity.

The volume in the Menindee Lakes increased slightly to reach 99% of capacity. This is due to the flood flows from the New South Wales Border Rivers and Southern Queensland tributaries flowing down to the Lower Darling system.

In contrast, by the end of April, the combined storages in the Wimmera–Mallee region of the Murray–Darling Basin are only 31% full, mainly due to the below average rainfall over the summer season.

Further detail on individual Murray–Darling Basin catchments can be found in the Murray–Darling Basin Water Information Portal.

Product code: IDCKGD0AR0

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.

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