THE NATIONAL ACADEMIES OF SCIENCES, ENGINEERING, AND MEDICINE
Division on Earth and Life Studies
Board on Atmospheric Sciences and Climate and Water Science and Technology Board
Committee on Modernizing Probable Maximum Precipitation Estimation
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Congressional Briefing
Tuesday, June 18, 2024 – 11:00 a.m.
via Zoom
on
Modernizing Probable Maximum Precipitation Estimation
For more than 75 years, high-hazard structures in the U.S., including dams and nuclear power plants, have been engineered to withstand floods resulting from the most unlikely but possible precipitation, termed Probable Maximum Precipitation (PMP).
Requested by Congress in P.L. 117-229, Further Continuing Appropriations and Extensions Act, 2023, this new report, from the National Academies of Sciences, Engineering, and Medicine, recommends a new definition of PMP and presents a vision for a methodology relevant for design, operation, and regulation of critical infrastructure. The new definition targets precipitation depths with an extremely low exceedance probability instead of assuming rainfall is bounded and considers specified climate periods so that PMP estimates can change as the climate changes. Near-term enhancements to PMP include improved data collection, model-based storm reconstructions, and strengthened scientific grounding for PMP methods. Long-term model-based PMP estimation will employ kilometer-scale climate models capable of resolving PMP storms and producing PMP-magnitude precipitation. A Model Evaluation Project will provide scientific grounding for model-based PMP estimation and determine when transition to a model-based PMP estimation should occur. Scientific and modeling advances along this front will contribute to addressing the societal challenges linked to the changes in extreme storms and precipitation in a warming climate, which are critical steps to ensuring the safety of our infrastructure and society.