CEE Seminar: The Hydrology of the Conterminous U.S. - What’s Changing and What Isn’t?
University of California, Los Angeles
Department of Geography
Bio: Dennis P. Lettenmaier (Ph.D., University of Washington, 1975) is a Distinguished Professor with interests in hydrologic modeling and prediction, hydrology-climate interactions and hydrologic change. He is an author or co-author of more than 300 journal articles. Lettenmaier was the first chief editor of the American Meteorological Society Journal of Hydrometeorology and is a past president of the Hydrology Section of the American Geophysical Union. He is a fellow of the American Geophysical Union, the American Meteorological Society and the American Association for the Advancement of Science, and is a member of the National Academy of Engineering.
Abstract: A central premise of most hydrologic risk analysis is stationarity, the assumption that the probability distribution of hydrologic quantities (especially extremes) do not change with time. This assumption is now widely questioned as we have better documentation of the effects of land cover change, climate change and water management on hydrologic fluxes including precipitation, runoff and evapotranspiration. Long-term changes in hydrological fluxes are well documented in California, which has just emerged from a four-year drought; the Colorado River basin, which remains mired in a drought of duration more than a decade; and other Western U.S. river basins. On the other hand, the case is less clear for historical changes in hydrologic extremes, such as floods and droughts. I review evidence -- mostly from the Western U.S., but more broadly where available -- from multiple hydrological records that in some cases now exceed 100 years in duration, including long-term streamflow records, as well as precipitation extremes for over 200 of the world’s largest urban areas, snow water equivalent (SWE) and other hydrologic variables. I discuss, in particular, temperature-related changes in snow processes in the Western U.S., including recent studies of the exceptionally low-snow winter of 2015-2016 across much of the West (for which California essentially was “ground zero”) and the possible shift of droughts in the Colorado River basin from precipitation to temperature control.
Reception following seminar: 4 to 6 p.m., Colloquia Room (EH 2430)
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