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Highlights in this update

•    The impact of drought continues to ease across the Murray–Darling Basin 
•    Total rainfall decreased across the Basin with some areas experiencing below average rain
•    A negative Indian Ocean Dipole (IOD) event is likely to continue into spring  
•    Spotlight story: Hume Dam water releases increase to create airspace and reduce future flood impacts

Rainfall deficiency for the Murray-Darling Basin, 12 months to August 2021

Drought

Water storages in the Basin have continued to fill despite a decline in rainfall during August. As of 1 September 2021, the Hume Dam was sitting at 95% capacity while several smaller storages in the northern Basin reached 100% capacity.

Although the drought persists, the increase in storages across the Basin is a positive sign and the risk of flooding downstream of the Hume Dam is being monitored closely by the MDBA and its partner agencies.

According to the Bureau of Meteorology rainfall deficiencies in the Murray–Darling Basin have continued to ease. Between 1 September 2020 and 31 August 2021, rainfall deficiencies were no longer appearing as severe or the lowest on record across the Basin. However, some parts of South Australia and Victoria are continuing to display serious deficiency across this 12-month period. Serious rainfall deficiency means an area has received rainfall in the lowest 10% of historical observations for a specified period.

The Bureau maintains that persistent and above average rainfall is still needed for the Basin to recover fully from drought, especially in South Australia, Queensland and far west New South Wales.

Rainfall across the Basin for August 2021.

Rainfall and temperature

August brought with it average to below average rainfall across the Murray–Darling Basin.

While most of the northern Basin experienced average rainfall, areas of the southern Basin saw mostly below average rainfall, particularly in the western catchments.

As seen in the graphic to the left, the western and northern catchments received 5–10 mm of rainfall during August, while falls in the eastern ranges ranged from 10–50 mm. Meanwhile, central areas of the Basin experienced rainfall totals of 5–10 mm. This is a contrast from June and July 2021 when rainfall totals were higher across much of the Basin.

In the northern Basin, average August rainfall  was experienced in St George (15.2 mm), Toowoomba (15 mm), Warwick (21. 8 mm), and Applethorpe (30.8 mm). Applethorpe experienced the coldest August day in Queensland at 9.8 °C on 24 August and the coolest on average overall at 10 °C. Meanwhile, St George experienced the strongest wind gust in Queensland at 78 km/h on 24 August.

In the southern Basin, the Victorian towns of Mildura (11.8 mm), Nhill (16.8 mm), and Kyabram (26.6 mm) experienced low rainfall. Mildura also experienced the hottest August day for Victoria at 27.6 °C on 31 August.

In South Australia, Loxton (15 mm) and Meningie (45.2 mm) experienced average rainfall. While in New South Wales, Broken Hill (9.4 mm) and Wilcannia (11.4 mm) also experienced average rainfall.

Water storage levels across the Basin as at 1 September 2021

Water storages and streamflow

Public water storages across the Murray–Darling Basin continued to increase across August and were holding 18,556 GL (83%) as of 1 September 2021. This was an increase from 77% in July 2021.

Public storages in the northern Basin increased significantly and were holding 3,812 GL (81%). This was an 8% increase from July 2021 when the northern Basin was holding 3,433 GL (73%).

This increase saw some public storages in the northern Basin increase to 100%, as of 1 September 2021. In the Border Rivers catchment, Pindari Lake was at 100% capacity while Lake Coolmunda was at 101%. In the Condamine–Balonne catchment, Chinchilla Weir was at 100%, while in the Namoi catchment, Chaffey Dam was at 103%. With several of these dams exceeding 100% they are now above their capacity and are surcharging.

Meanwhile, storages in the southern Basin have continued to steadily increase. As of 1 September 2021, southern Basin storages were holding 13,538 GL (83%). This is a 5% increase from 4 August when storages in the southern Basin were 12,640 GL (78%) and an increase from the end of June when storages were 10,316 GL (63%).

Although rainfall reduced during August, storage volume at Hume Dam continued to increase, rising to 95% as of 1 September 2021. Meanwhile, Menindee Lakes increased to 89%.

Climate outlook – negative Indian Ocean Dipole event likely to persist through spring

The negative Indian Ocean Dipole (IOD) event is likely to persist into November. The negative IOD will increase the chance of above average spring rainfall for the Murray–Darling Basin. This will see high streamflows for most of the northern and southern Basin leading into October.

Where soils in catchments are wet and streamflows are high further rainfall will increase the risk of flooding, particularly in parts of the southern Basin.

Meanwhile, night-time spring minimum temperatures are likely to be above average across the Basin while daytime minimum temperatures are likely to range from average to below average.

According to the Bureau of Meteorology, the tropical Pacific Ocean is likely to cool in the coming months. But this cooling may increase the chances of above average spring rainfall for much of the Basin.

Summary of threats to water quality in the Basin - September 2021

Water quality

Water quality issues continue to be assessed, with an overall lower risk 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.
  • Bushfire contamination remains a possible threat in the upper Murrumbidgee, upper Murray and Ovens catchments following rainfall. This risk will reduce as areas recover from bushfire damage.

Spotlight: Hume Dam water releases recommence to create airspace and reduce future flood impacts

Video: The Hume Dam is now effectively full and the MDBA increased releases to 31GL a day from Tuesday 7 September. (Source: WaterNSW)


With the Hume Dam at 98% capacity as of 7 September, the Murray–Darling Basin has increased daily releases to 31GL to create airspace within the dam.

This flow rate will keep River Murray levels a little above channel capacity but below minor flood level at Albury. The release rate is likely to change in response to changing conditions in the catchment.

As of Tuesday 7 September, the Hume Dam was effectively full. The MDBA is actively managing the storage and river operators are working around the clock to assess new inflow and weather information and manage releases in close consultation with the Bureau of Meteorology and WaterNSW.

Due to the limited airspace, there is now a high chance of flooding downstream of Hume Dam if future heavy rainfall events occur.

The MDBA operates the Hume Dam in accordance with the rules set by state governments.

To keep the local community informed the MDBA has been hosting weekly briefings with downstream stakeholders. Hume Dam river operations video updates have also been published either weekly or when conditions have changed and are available through the MDBA website or Weekly report.

Hume Dam’s primary purpose is water security – it plays a crucial role in managing flows and securing water along the River Murray, including to Adelaide. The MDBA needs to fill Hume Dam before irrigation demands start to exceed inflows, and the level starts to drop. This ensures water allocations are maximised.

The MDBA’s priority is to keep the dam safe, capture and store water, and where it can, mitigate floods.

If you live or work on the floodplain, you need to be prepared for potential floods by:

For more information about how dams are managed to reduce the impact of flooding visit the MDBA website.