Near-term projections of hydro-meteorological extremes over the United States

English Abstract:

We present near-term projections of hydro-meteorological extremes over the U.S. from a hierarchical high-resolution regional modeling framework that consists of the dynamical downscaling of 12 Global Climate Models (CCSM4, ACCESS1-0, NorESM1-M, MRI-CGCM3, GFDL-ESM2M, FGOALS-g2, bcc-csm1-1, MIROC5, CanESM2, MPI-ESM-MR, IPSL-ESM-MR, CMCC-CM5) from the 5th phase of Coupled Model Inter-comparison Project at 4km horizontal grid spacing. Our modeling framework uses a combination of a regional climate model (RegCM4) and a hydrological model (VIC). All models’ integrations consist of 41-years in the historic period (1965-2005) and 41-years in the near-term future period (2010-2050) under the RCP 8.5. RegCM4 domain covers the continental U.S., and the parts of Canada and Mexico at 18km horizontal grid spacing whereas VIC domain covers the continental U.S. at 4km horizontal grid spacing. We apply SOM cluster analysis technique to identify the atmospheric patterns associated with the hydro-meteorological extremes and effect of their future variations on the frequency and intensity of climatic extremes in the coming decades. The high-resolution ensemble shows substantially better skill in the simulation of hydro-meteorological extremes and associated atmospheric patterns in the historical period. Further, we find that while extreme heat waves show a significant increase in their occurrence in the coming decades, extreme cold waves are not projected to significantly decrease even when mean daily minimum temperatures are increasing. We also find an overall increase (decrease) in the inflows to the flood-controlling (hydroelectric) reservoirs across the United States. Such changes in the hydro-meteorological extremes could have substantial impacts on natural and human systems across the U.S.