Understand the Effects of Climate on Probable Maximum Precipitation and Flood

The Science

A high-resolution, numerical modeling framework was established and used by researchers from Oak Ridge National Laboratory (ORNL) to simulate the probable maximum precipitation (PMP) and flood (PMF) in a changing environment.  An increase in the deterministic PMP storm upper bound is projected through two different modeling approaches, suggesting a high likelihood of PMP enhancement in a warming climatic environment.

The Impact

PMP is the largest rainfall depth that could physically occur under a series of adverse atmospheric conditions.  It is the design standard of highly important energy-water infrastructures such as dams and nuclear power plants.  The increase of PMP has significant implications for our coupled energy-water security. New techniques developed here can help inform our understanding of PMP.


Probable maximum precipitation (PMP) and flood (PMF), defined as the largest rainfall depth and flood event that could physically occur under a series of adverse atmospheric and hydrologic conditions, have been an important design criterion for critical infrastructures such as dams and nuclear power plants in the United States. To understand how PMP and PMF may respond to projected future climate forcings, we used a physics-based numerical weather simulation model to estimate PMP across various durations and areas over the Alabama-Coosa-Tallapoosa river basin in the southeastern United States. Six sets of Weather Research and Forecasting model experiments driven by both reanalysis and global climate model projections, with a total of 120 storms, were conducted. ORNL results showed that PMP driven by projected future climate forcings is higher than 1981-2010 baseline values by around 20% in the 2021-2050 near-future and 44% in the 2071-2100 far-future periods. The additional sensitivity simulations of background air temperature warming also showed an enhancement of PMP, suggesting that atmospheric warming could be one important factor controlling the increase in PMP. In light of the projected increase in precipitation extremes under a warming environment, the reasonableness and role of PMP deserves more in-depth examination.

Principal Investigator(s)

Shih-Chieh Kao
Oak Ridge National Laboratory


This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Integrated Assessment Program, and Oak Ridge National Laboratory (ORNL) Laboratory Directed Research and Development Program. ORNL is managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05- 00OR22725.


Rastogi, D., S.-C. Kao, M. Ashfaq, R. Mei, E. D. Kabela, S. Gangrade, B. S. Naz, B. L. Preston, N. Singh, and V. G. Anantharaj. 2017. “Effects of Climate Change on Probable Maximum Precipitation: A Sensitivity Study over the Alabama-Coosa-Tallapoosa River Basin,” J. Geophys. Res.-Atmos. 122:4808-4828. DOI: 10.1002/2016JD026001.