Projections of Midwestern Warm-Season Rainfall Extremes from Dynamical Downscaling

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Tuesday, 4 February 2014: 11:15 AM
Room C102 (The Georgia World Congress Center )
Keith J. Harding, University of Minnesota, St. Paul, MN; and P. K. Snyder

Handout (26.9 MB)

The Central United States contains some of the most productive farmland in the world despite significant vulnerability to precipitation extremes. Climate change is expected to enhance hydrological extremes, producing more droughts and heavy rainfall events globally. How precipitation extremes might change over the Central U.S. is unclear because GCMs, with coarse spatial resolution, often struggle to adequately simulate hydrological extremes regionally. However, the higher spatial resolution of dynamically downscaled climate model projections can allow for investigation of future changes in extreme rainfall events and the possible mechanisms contributing to their intensification. In this study, we downscaled two models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) using the Weather Research and Forecasting (WRF) model for one historical period (1990-1999) and two future periods (2040-2049, 2090-2099) in a mid-range emissions scenario (RCP4.5). The diurnal cycle, extremes, and averages of precipitation in historical simulations are reasonably estimated. This enables us to examine how extreme rainfall events and the character of convective precipitation may be altered by climate change and to investigate possible dynamical mechanisms. In future simulations, more heavy rainfall events occur at the expense of lighter rainfall events, resulting in fewer total days with warm-season precipitation and more extended dry periods. Large increases in heavy rainfall events occur throughout the Central U.S., with the greatest change in the South Central region. Longer dry periods are present throughout most of the model domain, but the greatest increase in drought length occurs in the western Plains. Changes in environmental variables near the center of extreme rainfall events were examined to determine physical processes that may contribute to the increase in extreme rainfall events simulated by WRF. Possible mechanisms that contribute to the intensification of rainfall extremes in the region will be discussed.