Intercomparison of regional climate simulations of the 1991 summer monsoonin eastern Asia

Regional climate models have become a common research tool for downscaling global climate simulations. To further examine their usefulness for climate studies and the impacts that different physical parameterizations have on the simulations, an intercomparison experiment has been performed where thr ee regional climate models are used to simulate an extreme flood event. Alt hough the dynamical components of the models are almost identical, the phys ical parameterizations used to represent clouds, radiative transfer, turbul ence transport, and surface processes are very different. The models were u sed to simulate the heavy precipitation during the 1991 summer which caused severe flooding over the Yangtze River in China. This extreme event is sel ected to highlight the differences among regional climate models. Results f rom the intercomparison show that all models simulated the gross flood cond itions reasonably well, although each model reproduced the observed rainban d to varying degrees, and significant differences are found in the simulate d energy and hydrological cycles, especially over cloudy areas. Through det ailed analyses of model simulations at different spatial and temporal scale s, several reasons are found to cause the departure of model simulations fr om each other. These include the simulation of the amount and vertical dist ribution of clouds, the treatment of cloud-radiative feedbacks, and the rep resentation of land surface processes. This study suggests that aspects oth er than surface temperature and precipitation of the regional climate simul ations need to be more carefully evaluated. One specially important evaluat ion criterion is the radiation balance which has serious implications for l ong-term climate simulations.