Precipitation and Snowpack Dynamics over Mountains in the Interior Western US in a Changing Global Climate

This work first examines the performance of a regional climate model in capturing orographic precipitation and snowpack dynamics in interior western US. The Weather Research and Forecasting (WRF) model is run at a sufficiently fine resolution (4-km horizontal grid spacing), over a sub-continental domain driven by the Climate Forecast System Reanalysis (CFSR), to examine WRF's ability to simulate the observed seasonal precipitation and snowpack dynamics. WRF retrospective simulations are being run over a 30-year period from 1980 to 2010. Observations from Snow Telemetry (SNOTEL, providing precipitation rate and snowpack snow water equivalent (SWE)) and the Parameter-elevation Regressions on Independent Slopes Model (PRISM, providing fine-scale monthly mean values of precipitation and temperature) are used for validation. The results show that WRF captures observed seasonal precipitation and snowpack build-up reasonably well. The second part of this work assesses the future changes of orographic precipitation and snowpack. A pseudo-global warming (PGW) technique is used to perturb the retrospective reanalysis with the anticipated change according to the consensus global model guidance under the CMIP5 “high emissions” (RCP8.5) scenario produced by CMIP5 multiple model ensemble mean climate. This technique preserves low-frequency general circulation patterns and the characteristics of storms entering the domain. The WRF model is rerun over 30 years centered on 2050 with perturbed initial and boundary conditions. The results are used to examine the effect of climate variability and projected global warming on the statistical distributions of precipitation amounts and SWE in the studied domain