Research within EPA’s National Exposure Research Laboratory has been conducted for more than eight years to develop and refine a methodology to dynamically downscale the Weather Research and Forecasting (WRF) model at 36-km grid spacing. Those studies included a focus on simulating extreme events, methods of constraining WRF to the GCM, improving the representation of convective cloud cover, and improving the representation of inland water bodies in downscaled simulations. That research led to several dynamically downscaled climate change simulations that were used for air quality and human health studies.
In this study, dynamical downscaling using the WRF model is extended to a 12-km grid covering the contiguous U.S. The 12-km simulations are updated to use a current version of WRF and several scientific advances that have been made within the WRF model. Sensitivity to the use of mosaic land use information with the Noah land surface model is investigated, as is the sensitivity to the use of an alternative planetary boundary layer scheme. A global reanalysis dataset, the 0.75° × 0.75° ERA Interim, is used as a proxy GCM for evaluation of historical WRF simulations conducted with a 36- and 12-km nested grid configuration over a 1-year period. The added value of the 12-km grid will be assessed based upon whether its results are more accurate than those of the coarser parent grid. The ability of the simulations to accurately simulate extremes in minimum and maximum daily 2-m temperatures, as well as heavy rainfall events, will be investigated.