High-resolution ensemble projections of near-term regional climate over the continental United States

We present high-resolution near-term ensemble projections of hydroclimatic changes over the contiguous U.S. using a regional climate model (RegCM4) that dynamically downscales 11 global climate models from the fifth phase of Coupled Model Intercomparison Project at 18km horizontal grid spacing. All model integrations span 41years in the historical period (1965-2005) and 41years in the near-term future period (2010-2050) under Representative Concentration Pathway 8.5 and cover a domain that includes the contiguous U.S. and parts of Canada and Mexico. Should emissions continue to rise, surface temperatures in every region within the U.S. will reach a new climate norm well before mid 21st century regardless of the magnitudes of regional warming. Significant warming will likely intensify the regional hydrological cycle through the acceleration of the historical trends in cold, warm, and wet extremes. The future temperature response will be partly regulated by changes in snow hydrology over the regions that historically receive a major portion of cold season precipitation in the form of snow. Our results indicate the existence of the Clausius-Clapeyron scaling at regional scales where per degree centigrade rise in surface temperature will lead to a 7.4% increase in precipitation from extremes. More importantly, both winter (snow) and summer (liquid) extremes are projected to increase across the U.S. These changes in precipitation characteristics will be driven by a shift toward shorter and wetter seasons. Overall, projected changes in the regional hydroclimate can have substantial impacts on the natural and human systems across the U.S.