Dam management rainfall predictors haven't been updated for two decades, researchers say

The dam, upstream from the Lachlan River, spilled 230,000 megalitres on Monday amid torrential rain and further escalated flooding to already severely impacted communities.

The spill comes as new research on prediction models for rainfall, used in the construction and management of dams, found the 'Probable Maximum Precipitation' (PMP) calculation had not been updated for at least 20 years and did not factor in a rapidly warming climate.

The industry-funded research, by the University of New South Wales (UNSW) and the University of Melbourne, showed 546 dams across Australia would see average depth of rainfall jump between 14 and 38 per cent due to increased moisture in the atmosphere.

University of Melbourne hydrology and water resources Professor Rory Nathan said climate change would increase variability of weather in the already highly volatile Australian climate.

"We don't have any evidence to say that the event we're seeing at Wyangala is a result of climate change, but what we can say very clearly is there is a strong likelihood we're going to see these large floods increasing in frequency and intensity with climate change," he said.

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University of New South Wales professor in the school of Civil and Environmental Engineering Ashish Sharma said the "horrifying" situation of a dam failing was unlikely but predictors needed to keep up with a changing climate to manage risk.

"A dam is as potentially catastrophic as a nuclear power plant ... and the risk of this failure is something that we basically keep to the barest minimum that is acceptable," he said.

"Because the temperature is warming and you're storing and so much more moisture in the atmosphere ... the risk with which such a failure could occur when the dams were constructed was much lower than the risk we are seeing now.

"The risk will increase much, much more by the end of the century."

Corrective measures, such as auxiliary spillways or raising in the height of a dam wall, were common ways to manage impacts of increased rainfall to a dam, he said

In 2019, the NSW state government committed to raising the Wyangala Dam's wall by 10 metres to increase its storage capacity by 53 per cent.

Premier Dominic Perrottet on Tuesday reiterated the promise but was unable to provide a timeline for when the project would be delivered.

University of Melbourne's Professor Nathan said bigger dams and higher flood levees were just one part of the work for dam safety and flood mitigation.

"These are all things that need to be considered but if I was to spend a dollar, it would be on how best to reduce our carbon emissions, making decisions and treating the climate change as a crisis" he said.

"We've got to make sure people making decisions and all levels of government and in all boardrooms actually recognise this and are making decisions about what's best for the long term future."

Wyangala Dam spill levels have dropped since Monday, but towns downstream, including Forbes and Eugowra, are still feeling the effects.

More rain is forecast for the region over the weekend although weather is predicted to be less severe than the weekend before.