Regional climate model simulation of precipitation in central Asia: Mean and interannual variability

We examine how well the National Center for Atmospheric Research (NCAR) reg ional climate model (RegCM2) simulates the mean and interannual variability of precipitation in a semiarid region to more fully establish the strength s and weaknesses of the model as a tool for studying regional scale climate processes, We compare precipitation observations with RegCM2 output from a 5.5 year long simulation of the climate of central Asia, driven by the Eur opean Centre for Medium-Range Weather Forecasts analyses. RegCM2 simulates well the spatial patterns and annual cycles of precipitation observed in cl imatically different subregions. The magnitude of simulated precipitation i s similar to observations except over the driest part of Central Asia where the simulated precipitation is too high. We calculate precipitation anomal ies for each month as the difference between the monthly total and the 5 ye ar average for that month, from both observations and RegCM2 output. The ma gnitude of simulated interannual variability is similar to observations, al though there are differences. RegCM2 tends to underpredict (overpredict) th e magnitude of variability in the same combinations of subregion and season for which it underpredicts (overpredicts) mean precipitation. RegCM2 close ly reproduces precipitation anomalies observed in specific months, except d uring summer and during winter in the mountains. There is no correlation be tween model biases in mean precipitation and how well the model reproduces a series of precipitation anomalies, This suggests that the processes contr olling the mean and the variability of precipitation differ. Therefore eval uating the ability of a regional climate model to simulate both quantities is a demanding test of model performance.