Outdated rainfall modelling could risk critical failures in large infrastructure projects, including dams, for failing to accommodate climate change, according to new research from the University of New South Wales (UNSW) and the University of Melbourne.

Researchers found that ‘Probable Maximum Precipitation’ (PMP) estimates for 546 large dams across Australia are expected to increase between 14 and 38 per cent on average due to increasing atmospheric moisture.

The research suggests that existing dams will be at greater risk under climate change than what is currently assumed.

The academics say existing models of probable maximum precipitation have not been updated for at least 20 years, and more recent meteorological events already show that the climate is warming and making storms more intense and more frequent.

The lead author for the soon to be published paper, Johan Visser, said some of the world’s largest and most dangerous floods have been caused by dam failures.

“The problem is that PMP calculation is based solely on historical data with no consideration for future climate conditions. This means that many large dams constructed decades ago were designed using information representative of a cooler climate,” Mr Visser said.

“The purpose of this research was to analyse whether PMP estimates have changed over the last six decades and how these estimates might change in the future if we take into consideration a potential increase in atmospheric moisture due to known climate change.”

The new research – which was funded by ten of Australia’s leading water providers and dam owners – reanalysed existing meteorological records, added in more up-to-date data from the last 20 years that was not previously included, and then calculated potential changes in the future by incorporating the latest climate scenario modelling from the highly-respected Coupled Model Intercomparison Project Phase 6 (CMIP6).

These climate models are used to explore how a range of global socioeconomic choices over the next century will affect greenhouse gas emissions.

The results of the paper published in Water Resources Research show that PMP estimates have increased across Australia over the past 60 years and are expected to increase further due to predicted increases in atmospheric moisture.

Based on the trajectory of the observed data, it was evident that there would be a systematic increase in the PMP. This was confirmed using climate model simulations, indicating further increases for every climate scenario analysed.

For the worst-case future scenario, where green policies are not implemented and carbon emissions remain highest through to the year 2100, PMP estimates over large dam locations in Australia could increase by 38 percent on average.

Even using the most conservative (low) estimates regarding emissions and subsequent climate change, the modelling suggests an average increase in PMP of 13 per cent across Australia.

The researchers say they have shown the current method of calculating PMP is likely outdated and does not take into consideration the potential consequences of current changes in atmospheric conditions, let alone those predicted into the future.

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