The rainfall model that engineers use to help them design critical infrastructure such as large dams and nuclear power plants needs to be updated to take into account climate change.
That is the conclusion of a study paper to published in Water Resources Research, which calculates that the ‘Probable Maximum Precipitation’ estimates for 546 large dams across Australia is expected to increase between 14 and 38 percent 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.
“There are a lot of risks involved with dams given the amount of water they are holding back. Some of the worst floods around the world were due to extreme storms overwhelming a dam, causing it to fail and release a wall of water downstream,” says Johan Visser from UNSW Sydney’s Water Research Centre, who was lead author on the paper in collaboration with academics from the University of Melbourne.
“Engineers design dams to accommodate the largest flood event that could reasonably be expected to occur at a particular location, known as the Probable Maximum Flood (PMF). To work that out, you first need to calculate what is the greatest depth of rainfall meteorologically possible over that area in a certain amount of time, which we call the Probable Maximum Precipitation (PMP).
“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.
“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 current probable maximum precipitation guidelines for various timeframes and locations across Australia is collated and published by the Bureau of Meteorology.
The new research – which was funded by 10 of Australia’s leading water providers and dam owners from across Australia – 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 in 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.