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Highlights in this update

  • December was warmer and wetter than average
  • Blue-green algae alerts remain in place for much of the River Murray in the southern Basin
  • Water storage levels across the Basin were steady through December
  • Spotlight story: A tale of two Basins
Rainfall deciles for previous 36 month period, showing rainfall was well below average throughout the Basin

Drought

Despite drought-breaking rain in some parts of the Murray–Darling Basin over the past couple of months, the northern Basin continues to endure prolonged drought conditions.

According to the Bureau of Meteorology (BoM), December rainfall was the fourth highest on record for Australia, however it was only slightly above average for the entire Murray-Darling Basin.

In the northern Basin rainfall in the Paroo, Moonie, Gwydir, Namoi, Peel and Castlereagh catchments resulted in minor to moderate inflows. Despite this, NSW northern Basin catchments are at Stage 2 Drought (except for the Macquarie – Stage 1) and cease-to-flow conditions are occurring along the Darling River below Bourke. All Queensland Murray–Darling Basin catchments remain drought declared.

A further look at how drought is affecting the northern Basin is provided in this month’s spotlight story.

Rainfall totals for December 2020, showing rainfall across the entire Basin.

Rainfall

December 2020 was warmer and wetter than average, with mean temperatures across the Basin 0.5 °C above the long-term average and rainfall above the long-term average for nearly 70% of the Basin. Rainfall over the month was very patchy, with some areas experiencing heavy rainfall and flash flooding while others received very little.

While rainfall was average for most parts of the Basin, it was above average to well above average in the Paroo, NSW Border Rivers, Namoi, Gwydir and Macquarie-Castlereagh catchments.

The Bureau of Meteorology continues to advise persistent and widespread above average rainfall is needed to turn around long-term rainfall deficiencies especially in northern parts of the Basin where total storage levels remain low.

Water storage levels across the Basin for December 2020

Water storages and streamflow

Public water storages across the Basin were holding 12,098 GL (54%) as at 6 January 2021. This was down from 67% in November but 29% more than the same time last year. Public storages in the northern Basin were holding 1,281 GL (27%). This was steady from 1 December 2020 but up 6% compared to 1 January 2020.

Many public storages in the northern Basin remain below 30% with the exceptions of storages in the Namoi (Chaffey Dam at 44%, Burrendong Dam at 42%) and the smaller storages in the Condamine-Balonne (Chinchilla Weir at 44% and Jack Taylor Weir at 62%).

As of 6 January 2021, southern Basin storages are holding 10,049 GL (62%). This is up from 37% at the beginning of 2020 but down from 69% in early November 2020.

In the northern Basin heavy but patchy rainfall has provided unregulated flows into the Barwon-Darling system. As of 5 January 2021, 27 GL of unregulated flows passed Walgett. WaterNSW says these minor flows are not expected to reach much further than Louth.

In the River Murray, the December flow to South Australia comprised of water for South Australia’s entitlement, as well as traded volumes and water for the environment.

Climate outlook for summer and autumn

The BoM forecasts that the 2020-21 La Niña is likely to have peaked but will continue to bring wetter than average conditions into early autumn. The BoM predicts that between February and April there is a 60% to 75% chance of exceedng median rainfall in the Basin, with the highest chance in Queensland catchments.

The Southern Annular Mode (SAM) that was strongly positive over previous months has decreased towards neutral where it is expected to stay until the start of February. This decreases the chance of above average rainfall for eastern Australia.

In light of recent rainfall and the positive seasonal rainfall forecasts, WaterNSW continues to work with BoM to assess the likelihood of NSW storages filling over the coming months, particularly Burrinjuck Dam, and prepare for pre-releases and potential flood operations, if necessary. WaterNSW warns that floods and floodplain flows that occur in the coming months may trigger poor water quality, particularly low dissolved oxygen for fish, as floodwaters may pick up significant amounts of accumulated leaf litter and other organic material.

Summary of threats to water quality in the Basin - January 2020

Water quality and salinity

Water quality issues continue to be assessed, with some risk of hypoxic blackwater due to forecast wet conditions in the southern Basin and an increase in blue-green algae occurrence in line with seasonal expectations.

The MDBA and state authorities continue to monitor water quality across the Basin. For more information on water quality, and a map of threats, see the water quality page of our website.

Summary of key water quality issues

  • Blue-green algae: Many locations throughout the Basin are at risk of algal blooms. Conditions have the potential to change rapidly. For the latest information on blue-green algae alerts, contact the relevant state government contacts via the Getting information about current algal blooms page of our website.
  • Blackwater threats are possible in several southern Basin rivers, including the potential for hypoxic blackwater in the Murray, Murrumbidgee and Lachlan Rivers. State governments and the MDBA are monitoring and considering these threats.
  • Low dissolved oxygen threat levels range from possible to likely for several locations in the Basin, including the Lachlan and Barwon–Darling Rivers.
  • Bushfire contamination remains a possible threat in the upper Murrumbidgee, upper Murray and Ovens catchments. This risk will lower as areas recover from bushfire damage.

Spotlight: A tale of two Basins

Despite drought-breaking rain in some parts of the Murray–Darling Basin over the past couple of months, the northern region continues to endure prolonged drought conditions. In fact, the whole of the Queensland part of the Basin is still drought declared.

The upper reaches of the northern Basin are less resilient to drought than the southern Basin, having highly variable rainfall influenced by tropical weather patterns and fewer large storages to control flow through the river systems.

Northern Basin storage levels remain low. As at 6 January 2021 the Condamine catchment’s Beardmore Dam was at 15% and Leslie Dam at 12%. In the Border Rivers area, Coolmunda Dam was at 21% and Glenlyon Dam 15%.

Much of the rain has fallen downstream of the dams and is therefore not captured in public storage for future use.

Having received a healthy flow early last year, areas such as the Darling River are once again struggling with no-flow or disconnected river reaches south of Bourke.

To help support river ecosystems, the Commonwealth Environmental Water Holder is delivering water into the upper Barwon River system as part of the Northern Waterhole Top-up. Up to 6 gigalitres of water for the environment is being released, with 5.1 gigalitres from the Gwydir catchment and up to 0.9 gigalitres from the Macintyre River.  The New South Wales Government has provided an additional 2 gigalitres from the Macintyre River. At the beginning of January 2021, both these river systems received the most rainfall for months.

In contrast with the north, most of the southern Basin has benefited from reasonable rainfall in the past few months, and the La Niña weather system is forecast to deliver further follow-up rain. This rainfall has delivered healthy increases in allocations for some licence holders. For example, as of 15 January 2021, water allocations against general security and high security entitlements in the Murrumbidgee have reached 100%. In the previous two years water allocations only reached 11% and 7%.

Both dryland and irrigated annual crops have done well from steady rain, with farmers in the Murrumbidgee experiencing their strongest wheat, barley and canola yields in several years. Rice growing in the Murray region has also picked up again after a couple of years of no water allocations.


Image: The junction of the Namoi and Barwon Rivers, near Walgett in New South Wales (2020)