Sensitivity of Present and Future Seasonal Precipitation over Central United States to the Representation of Rocky Mountain Topography

Precipitation change across the Central United States is of great interest to the research community. Studies using global climate simulations, suggest that the “100^th-Meridian”, which separates the “dry west” from the “moist east” will shift to the east as the climate responds to future emissions pathways. However, these simulations are run at relatively coarse resolutions which do not accurately represent topography. Here we perform regional simulations using the Weather Research and Forecasting (WRF) model to explore the sensitivity of present and future precipitation patterns across the Central US to the representation of the Rocky Mountains. We first perform 20 km control simulations for both historical (1980-2009) and end-of-century (2070-2099) periods across the Continental US. These simulations are forced using the mean of a bias corrected ensemble of CMIP6 models at 1.25 degree horizontal resolution and six-hourly intervals. The end-of-the century runs use the SSP585 emissions scenario. We then run simulations where we decrease the height of the Rocky Mountains to 80% and 90% of the height in the control simulation. This emulates the “effective” height of the Rocky Mountains in coarser (1 – 2 degree resolution) global simulations. The results from these experiments will be shown with emphasis on the seasonality of changes in precipitation patterns, the impact of moisture transport, and the importance of properly representing Rocky Mountain topography in understanding projections of precipitation change across the Central US.