Thu, Oct 10, 2019 @ 04:00 PM - 05:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Dennis Lettenmaier, Ph.D., Department of Geography, University of California, Los Angeles
Talk Title: If extreme precipitation is increasing, why are not floods?
Abstract: Despite evidence of increasing precipitation extremes, corresponding evidence for increases in flooding remains elusive. If anything, flood magnitudes are decreasing despite widespread claims by the climate community that if precipitation extremes increase, floods must also. Based on a recent 2018 WRR paper Sharma, Wasko, and Lettenmaier I suggest reasons why increases in extreme rainfall are not resulting in corresponding increases in flooding. Among them are decreases in antecedent soil moisture, decreasing storm extent, and decreases in snowmelt. I further discuss a recent analysis that investigates linkages between antecedent soil moisture and flooding along the U.S. west coast both historically 1950-present and projected into the future using downscaled global climate model output. Our analysis shows some evidence of mitigation of extreme floods in a warmer climate due to changes in antecedent soil moisture and shifts in the seasonal timing of extreme precipitation. I also discuss an ongoing analysis of flood records from 110 stream gauges for unregulated streams across the western U.S. for the period 1950-2015, where each event was classified into one of six flood-generating mechanisms. This analysis shows few trends in the mix of flood generating mechanisms over the last 50 years, of flood magnitudes, or of the seasonal timing of floods. I argue that understanding the link between changes in precipitation and changes in flooding past and future is a grand challenge for the hydrologic community and is deserving of increased attention.
Host: Dr. George Ban-Weiss
Audiences: Everyone Is Invited
Posted By: Evangeline Reyes