REGIONAL NESTED MODEL SIMULATIONS OF PRESENT-DAY AND 2XCO2 CLIMATE OVER THE CENTRAL PLAINS OF THE US

A nested regional climate model is used to generate a scenario of clim ate change over the MINK region (Missouri, Iowa, Nebraska, Kansas) due to doubling of carbon dioxide concentration (2 x CO2) for use in agri cultural impact assessment studies. Five-year long present day (contro l) and 2 x CO2 simulations are completed at a horizontal grid point sp acing of 50 km. Monthly and seasonal precipitation and surface air tem perature over the MINK region are reproduced well by the model in the control run, except for an underestimation of both variables during th e spring months. The performance of the nested model in the control ru n is greatly improved compared to a similar experiment performed with a previous version of the nested modeling system by Giorgi et al. (199 4). The nested model generally improves the simulation of spatial prec ipitation patterns compared to the driving general circulation model ( GCM), especially during the summer. Seasonal surface warming of 4 to 6 K and seasonal precipitation increases of 6 to 24% are simulated in 2 x CO2 conditions. The control run temperature biases are smaller than the simulated changes in all seasons, while the precipitation biases are of the same order of magnitude as the simulated changes. Although the large scale patterns of change in the driving GCM and nested RegCM model are similar, significant differences between the models, and su bstantial spatial variability, occur within the MINK region.