Ten-year U.S. regional climate simulations for impact assessments

We have used two nested regional climate models, RegCM2 and the Danish Meteorological Center's HIRHAM, to produce suites of 10-yr climate simulations for the continental US at 50 km resolution. Three sets of driving boundary conditions - NCEP/NCAR reanalysis, Hadley Centre coupled atmosphere-ocean GCM (HadCM2) simulation of a contemporary climate, and HadCM2 simulation of a future climate - have been used to produce six 10-yr simulations (2 models x 3 sets of boundary conditions). Simulations with reanalysis boundary conditions provide a basis for evaluating regional model capability to produce mesoscale climate details over the US and also give a preliminary view of uncertainty in regional climate simulations from using different regional models. Comparisons of the reanalysis-driven simulations with the HadCM2 control climate-driven simulations indicate the extent to which biases in the GCM produce corresponding biases in the regional climate model results. Finally, comparison of regional model results driven by the two HadCM2 boundary conditions offers a view of consistency among models for simulating potential regional climate changes due to enhanced greenhouse gas radiative forcing. Calculations of changes in heating degree days, cooling degree days, growing degree days, and heat stress units demonstrate the use and uncertainty of such simulations in evaluating impacts of climate change on energy consumption and agricultural crops.