According to industry-funded research by UNSW and the University of Melbourne, there could be a greater risk of exceeding the flood capacity of dams due to outdated modeling of potential peak rainfall. The study, to be published in Water Resources Research, concludes that the rainfall model that engineers use to design critical infrastructure such as large dams and nuclear power plants needs to be updated to account for climate change.
The paper calculates that ‘Probable Maximum Precipitation’ (PMP) estimates – the greatest possible depth of rainfall – for 546 large dams across Australia are expected to increase by an average of 14 to 38 per cent due to atmospheric moisture. Scientists say existing PMP models have not been updated for at least 20 years, and recent weather events already show the climate is warming and storms are becoming more intense and frequent.
Lead author Johan Visser, from UNSW Sydney’s Water Research Laboratory, said there were many risks associated with dams, given the amount of water they hold. “Some of the worst floods in the world have been caused by extreme storms that inundated a dam, causing it to fail and releasing a wall of water downstream,” Visser said. “Engineers design dams to accommodate the largest flood that can reasonably be expected at a particular location, known as the Probable Maximum Flood (PMF). To work this out, you first need to calculate what is the meteorologically greatest depth of rainfall possible in that area for a certain a time we call PMP.
The problem is that the PMP calculation is based entirely on historical data, with no regard for future climate conditions. This means that many large dams built decades ago were designed using information representing a colder climate. “The purpose of this research was to analyze whether PMP estimates have changed over the past six decades and how these estimates may change in the future, given the potential increase in atmospheric moisture due to known climate change.”
Current PMP guidance for various time frames and locations across Australia is collected and published by the Bureau of Meteorology. University of Melbourne lead researcher Professor Rory Nathan said: “No country in the world has yet updated the operational procedures used to estimate PMP to account for climate change, and this research provides the first evidence that these procedures need to be reviewed.”
“Any increase in PMP estimates will lead to a corresponding change in PMF, but it will take time to work out how best to use these findings to better inform future decision-making. There are deep uncertainties in assessing impacts.” climate change, and this research reinforces the need to consider adaptive management approaches to allocate resources incrementally as our understanding of these growing risks improves.
“We are facing a climate crisis and this research adds to the urgency with which we must reduce our carbon emissions.” Funded by 10 of Australia’s leading water suppliers and dam owners from across Australia, the new research re-analyzed existing meteorological records, added more recent data from the past 20 years not previously included, and then calculated the potential. changes in the future by incorporating the latest modeling of climate scenarios from the highly respected Coupled Model Intercomparison Project Phase 6.
These climate models are used to examine how a range of global socio-economic decisions over the next century will affect greenhouse gas emissions. The researchers say they have shown that the current method of calculating PMP is likely outdated and does not take into account the potential consequences of current changes in atmospheric conditions, let alone those predicted for the future.
UNSW’s Professor Ashish Sharma, corresponding author of the paper, said: “This is an important piece of research not only for Australia but globally. The PMP approach is developed and recommended by the World Meteorological Organization and is used more or less consistently by countries around the world. Anyone planning to build a large dam needs to think 50 to 100 years ahead, and this research clearly shows that future planning now needs to consider the future impacts of climate change on the plausible upper limit of extreme rainfall.”
