Short-term rainfall deficiencies continue in south-east South Australia, southern Victoria, western Tasmania

May rainfall was below average for much of Victoria away from the north-west; an area of Western Australia between the Central West and Goldfields; and parts of the Top End, central Northern Territory and Kimberley in Western Australia.

Rainfall averaged over the 6 months from December 2021 has been below average for 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. Evaporative stress remains high for the four-week window ending 31 May 2022 across the areas experiencing serious or severe rainfall deficiency for the 6-month period.

Rainfall for May was above average for most of Queensland and New South Wales. For Queensland as a whole area-average rainfall was the 5th-highest on record for May (compared to all years since 1900). May rainfall was also above average for far north-west Victoria; pockets of South Australia about the eastern border, south coast, and central north; south-east Tasmania; and in Western Australia extending from the Pilbara coast and northern Gascoyne to the south-western corner of the Northern Territory.

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 was a reduced number of active Madden Julian Oscillation (MJO) events (i.e. monsoon bursts) during the second half of the wet season, resulting in below average rainfall since January 2022. A persistent pattern of MJO events stalling in the Indian Ocean and/or weakening rapidly as they approach Australia may have been influenced by very warm waters in the Indian Ocean.

The Climate Outlook released on 2 June 2022 indicates rainfall for June to August is likely to be above median for much of Australia. However, south-western Australia, and western Tasmania are likely to have below median rainfall.

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.

6-month rainfall deficiencies

May rainfall was below average for much of Victoria away from the north-west; an area of Western Australia between the Central West and Goldfields; and parts of the Top End, central Northern Territory and Kimberley in Western Australia.

Serious and severe rainfall deficiencies for the period December 2021 to May 2022, compared to all years since national records began in 1900, are in place across western to central Tasmania, the coast of far south-east South Australia, the south-west coast of Victoria and in an area to the east of Melbourne. Compared to the 5-month period ending April 2022 the strength of these deficiencies has decreased, with areas of lowest-on-record rainfall largely disappearing. However, the strength of deficiencies to the east of Melbourne has increased following below average rainfall for much of southern Victoria in May.

Serious or severe rainfall deficiencies at the 6-month timescale are also observed in the Northern Territory across the base of the Top End and in pockets of the central Top End. The latter part of the northern wet season was 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.

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Soil moisture

Root-zone soil moisture (soil moisture in the top 100 cm) for May 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 Territory away from the western Top End and eastern border with Queensland, for part of the south-east of the Kimberley, and for areas of inland Western Australia around the Goldfields Dsitrict, and for much of the South West Land Divison.

Soil moisture was above average for part of the south coast of Western Australia; the north-eastern Kimberley and western Top End; Queensland and along the eastern border of the Northern Territory; New South Wales except part of the inland south-east; north-western Victoria and much of Gippsland; much of Pastoral South Australia away from western districts; and east coast Tasmania.

Compared to last month, soil moisture has generally increased across eastern Australia and South Australia, although decreasing from very much above average to above average along much of the New South Wales coast and Gippsland. Soil moisture has generally decreased across Western Australia and the Northern Territory.

Saturated soil conditions across eastern Australia have been a significant contributor to the severity of flooding in recent months, although they have also contributed to increased inflows into water storages.

  • May rainfall was above average for Australia as a whole, and above to very much above average for most of Queensland, New South Wales, north-west Western Australia, and south-east Tasmania
  • Rainfall was below average for much of Victoria, an area of Western Australia between the Central West and Goldfields, and parts of the Top End, central Northern Territory and Kimberley in Western Australia
  • Serious rainfall deficiencies (totals in the lowest 10% of historical observations since 1900) continue to affect 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 parts of the central Top End
  • Major flood events occurred during May in inland central and northern Queensland and inland northern New South Wales
  • High streamflows were recorded in Queensland and New South Wales and in the Murray–Darling Basin, with many sites recording the highest flow on record for May
  • At the end of May, Australia's total storage volume was 69% of full capacity
  • Urban storages in all capital cities reached above 80% of capacity, except for Adelaide and Perth
  • Many storages in the Murray–Darling Basin are at full capacity
  • Storages in northern Australia increased during the monsoon season and remain above 70% capacity
  • The Bundaberg system reached to its highest storage levels since January 2019
  • 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 Queensland and New South Wales

Widespread significant rainfall in Queensland and northern and inland areas of New South Wales resulted in widespread riverine flooding in several catchments. Extended rainfall in the Gulf Country, Northern Goldfields, Sunshine Coast, Wide Bay and Burnett, and Central West regions of Queensland resulted in major flooding along the Bremer and Logan rivers, Warrill, Laidley, Lockyer and Sandy creeks (south-east Queensland), the Laidley Creek and Cape River (north-east Queensland), the Condamine and Balonne rivers (southern Queensland) and the Culgoa River (northern New South Wales).

High streamflow in Queenland and New South Wales

In May, average to very much above average rainfall over most of eastern Australia, and some parts of the Pilbara in the west, was reflected in the streamflow conditions of these regions. In the North East Coast, from Cape York to Brisbane, most of the streamflow gauges (with records at least from 1980) recorded very much above average streamflow, many with record-high streamflow for the month of May. In Queensland and New South Wales, most of the gauges observed above average streamflow. Record-high flows were observed in many sites in the southern Murray–Darling Basin. In contrast, streamflows were mostly below average in South Australia, western Victoria, and along the South West Coast of Western Australia.

Streamflow decile rankings across Australia
Streamflow decile rankings across Australia

Overall high storage levels across the country and most capital cities

By the end of May, the total water storage volume in Australia reached 69% of full capacity; similar to the previous month. Despite most of the major storage levels being high, there are individual pockets of low storage 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

Rainfall for May for coastal south-east South Australia was below average, contributing to reduced run-off and inflows into some of Adelaide's 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 May (up from 39.3% 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

Very much above average rainfall across Queensland during May resulted in increased storage volumes. In the Bundaberg system, the storage volume sharply increased by 29% compared to the previous month, reaching 86% at the end of May, the highest levels since February 2019. In the Nogoa Mackenzie system, storage levels increased during May by 4% with the volume reaching a slightly higher level than the same time last year but still remaining low.

Northern Australia water storage levels are above 70% 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 following relatively better conditions in the preceding winter season.

In May, the storage volume in Lake Argyle decreased by 3% and the Darwin River storage remained at full capacity, similar to the previous month.

Total storage volume in the Murray–Darling Basin remains high

During May, much of the Murray–Darling Basin received above average rainfall. At the end of May, the total water storage in the Murray–Darling Basin increased slightly (up by 1%) from the previous month to 86% of capacity at the end of May. Compared to the same time last year, when the total storage volume was only 59%, the water storages are generally in a much better position.

The total storage in the northern Basin was 94% of capacity at the end of May; slightly higher than the previous month, and significantly higher than the same time last year when it was only half full.

The total storage in the southern Basin remains similar to the previous month at 84% of capacity in May. 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 full capacity. This is due to the flood waters from the New South Wales Border Rivers and southern Queensland tributaries flowing down to the Lower Darling system.

In contrast, by the end of May, the combined storages in the Wimmera–Mallee region of the Murray–Darling Basin were only 30% full, mainly due to below average rainfall over the autumn season (i.e. March to May).

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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