Above average rainfall continues in the Northern Territory

December rainfall was above average for Australia as a whole, with the national area-average 33% above long-term mean. Rainfall was very much above average for the Northern Territory where area-averaged rainfall was the eighth-highest on record for December (compared with all Decembers since 1900) for the Northern Territory.

December rainfall was below average in north-eastern New South Wales and south-eastern Queensland, the western half of Tasmania, the southern region of Western Australia, and in some scattered parts of Victoria and South Australia. Rainfall was close to average in most parts of South Australia and Victoria, parts of Western Australia, eastern Tasmania, and much of the inland areas of New South Wales and Queensland. Rainfall was above average or very much above average (highest 10% of all Decembers since 1900) for most of the Northern Territory and Pilbara region in Western Australia.

The wet conditions during November in the north of the Northern Territory significantly eased rainfall deficiencies in that region. Above average rainfall continues in much of northern Australia during December, with the onset of monsoon (on 22 December at Darwin), and ex-tropical cyclone Ellie during the last week of December.

For the 13-month period starting December 2021, serious rainfall deficiencies (totals in the lowest 10% since 1900) remain in western Tasmania, and part of south-west Western Australia which slightly eased despite below average December rainfall in those regions.

Multi-year rainfall deficiencies, which originated during the 2017–2019 drought, have been almost entirely removed from the eastern states. The largest area of remaining multi-year rainfall deficiencies is in the Goldfields District of Western Australia, with smaller pockets in south-west Western Australia, north of the Northern Territory and northwest of Tasmania.

The long-range forecast released on 05 January 2023 indicates rainfall for January to March is likely to be above median in eastern parts of eastern states especially eastern Tasmania, southeastern New South Wales into eastern Victoria and parts of northern Queensland. Below median rainfall is likely for parts of the Top End, the Tiwi Islands, south-west Western Australia and isolated parts of Western Australia into the south-west corner of the Northern Territory and extending over western South Australia and the Eyre Peninsula.

Deficiencies for the 13 months since December 2021

Rainfall for December was above average for Australia with the national area-average 33% above long-term mean and it was amongst the eight highest on record for the Northern Territory. December rainfall was below average in north-eastern New South Wales and south-eastern Queensland, the western half of Tasmania, the southern region of Western Australia and in some scattered parts of Victoria and South Australia. Rainfall was close to average in most parts of South Australia and Victoria, parts for Western Australia, eastern Tasmania and much of inland New South Wales and Queensland. Rainfall was above average or very much above average (highest 10% of all Decembers since 1900) for most of the Northern Territory and Pilbara region in Western Australia.

For the 13-month period ending in December 2022, serious rainfall deficiencies (in the lowest 10% since 1900) are in place for a small pocket of western Tasmania, south-west Western Australia and in the north of Northern Territory. Compared with the 12-month period ending in November 2022, rainfall deficiencies have slightly increased in western Tasmania and slightly decreased in the Northern Territory.

December rainfall for the Northern Territory overall was the eighth-highest on record since 1900, most of which came from ex-tropical cyclone Ellie during the last week of the month. The first half of the month was dry, but the last half saw significant rainfall because of an active monsoon period and tropical cyclone Ellie which produced heavy rainfall over northern and central parts of the Territory, after falling to tropical low strength on making landfall on the western Top End coast early in the morning of 23 December. Total rainfall in these areas were very much above average (highest 10%) in November and December. As a result of the rain, deficiencies in the 13-month period ending in December 2022 were significantly decreased. This has almost removed the deficiencies accumulated during the poor end to the 2021–22 wet season. A small pocket of serious rainfall deficiencies remains near Elliott in the Barkly district.

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Soil moisture

Despite below average rainfall during December, root-zone soil moisture (soil moisture in the top 100 cm) was higher than average for most of Australia except south-west Western Australia which had average to below average soil moisture. Soil moisture was very much above average (highest 10% of all Decembers since 1900) in most parts of Victoria, inland New South Wales, and across parts of the tropics from the south-eastern Kimberley and western parts of Northern Territory, as well as parts of eastern Queensland.

In recent months, saturated soil conditions across south-eastern Australia have been a significant contributor to the severity of flooding and have also contributed to increased inflows into inland water storages.

Evaporative stress

Evaporative stress for the 4 weeks ending 4 January 2023 increased over much of inland Queensland and New South Wales and along the south and coast of Western Australia. Evaporative stress remains elevated for much of the Gascoyne and Goldfields districts, and for the South West, districts in Western Australia.

See the journal publication for further details on calculation and use of evaporative stress index in drought monitoring.

  • December Rainfall was below average in south-eastern New South Wales and south-eastern Queensland, and in seasonally dry areas of the south-west of Western Australia.
  • Serious rainfall deficiencies (totals in the lowest 10% of observations since 1900) for the period starting December 2021 remain for pockets in Northern Territory, western Tasmania and part of south-west Western Australia.
  • Rainfall was mostly average across much of the rest of the country except part of the northern tropics and the Northern Territory which was eighth-highest on record for December (national rainfall records start in 1900).
  • Soil moisture was above average for most of Australia except for parts of south-west Western Australia.
  • Low streamflows were observed mostly in south-west Western Australia and inland Queensland, and high streamflows at many southern Murray—Darling Basin sites.
  • At the end of December, Australia's total storage volume was 77.3% of full capacity with urban storages in all capital cities except for Perth (55.9%) sitting above 80%.
  • The combined storages in the Murray–Darling Basin were 100% full. This is up from 91% at the end of December 2021.
  • Australia's largest rural storage - Lake Argyle - has increased 5.3% in December.
  • Low storage levels continue in some parts of central Queensland, western Tasmania, south-east New South Wales, western Victoria and some urban storages for Perth and Western Australia.

Streamflows high in the south-east and low in south-west Western Australia

In December, above to very much above average streamflows (based on records since 1975) were observed in 37% of sites, mainly in the Murray—Darling Basin, southeast coast (Victoria), eastern Tasmania, north-west Western Australia, the Top End of the Northern Territory, and wet tropics of Queensland. In the Murray—Darling Basin, despite average to below average rainfall, streamflows were high because of the downstream movement of floodwater. Numerous flood warnings were issued for catchments across New South Wales and northern Victoria. High streamflows in the Northern Territory and Kimberly region were associated with the high rainfall from ex-tropical cyclone Ellie.

In December, streamflows were average at 33% of sites, mainly in north-east and western Australia. Lower than average streamflows were observed at 7% of the 879 sites, mostly associated with below average rainfall and drier catchment conditions in south-west Western Australia, southern Tasmania, inland Queensland, and at some scattered sites in south-eastern Australia.

Streamflow decile rankings across Australia
Streamflow decile rankings across Australia

Overall high storage levels across the country with a few pockets of low storages

In December, most of Australia except the Northern Territory, received average to below average rainfall. These resulted in a slight decrease in some storage levels from November, particularly in south-eastern and western Australia. By the end of December, the total water storage volume in Australia (across Australia's 306 public storages) was 77.3% of full capacity; slightly higher than the previous month and higher than at the same time last year. The combined storages in the Murray—Darling Basin were 100% full, up from 91% at the same time last year. Despite most of the major storages being at high levels, there remain several pockets of low storage volumes: particularly in central Queensland, Tasmania, and western Victoria.

Major storage levels across Australia
Major storage levels across Australia

Perth's surface water storages were just above half capacity at the end of December at 55.9% (down from 56.4% at the same time last 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.

Water storage in the Harding in the Pilbara region in Western Australia was just above half capacity at the end of December at 55.5% (up from 48.2% at the same time last year).

With above average rainfall in December, the storage volume in Lake Argyle increased by 5.3% and reached 66.7% of capacity (higher than 58.5% at the same time last year).

With drier catchment conditions across western Tasmania in previous months, storages volume in Tasmania remain around half of full capacity (55.3%) which is slightly lower (0.6%) than last month and also lower than at the same time last year.

Water levels in the Nogoa–Mackenzie system in central Queensland remain low despite increasing to 40.2% by the end of December (up from 28% at the same time last year). In central Queensland, water storage in Fairbairn was below half capacity at the end of December at 39.4% (up from 26.8% at the same time last year).

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

An overview of streamflow, stream salinity, and storage levels for Drainage Divisions across Australia can be found in the Monthly Water Update.

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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