Simulation with the regional climate model RegCM2 of extremely anomalous precipitation during the 1991 east Asian flood: An evaluation study

One of the potential applications of the regional climate model RegCM2 developed at the National Center for Atmospheric Research (NCAR) is to analyze and possibly forecast high-resolution spatial features of anomalous, short-term climate variations. To evaluate the ability of RegCM2 to predict anomalous precipitation, a simulation of the east Asian flood that occured during May through July 1991 was performed. This simulation was driven by large-scale atmospheric background derived from the European Center for Medium-Range Weather Forecast (ECMWF) analysis. We found that RegCM2 is capable of reproducing an anomalous rainbelt in the flood region from the Yangtze-Huai River Basin (eastern China) to southern Japan, and to produce local, strong rainfall centers within the belt. It reasonably well simulates the spatial patterns of the circulations, the anomalous early leap of the summer monsoon to the flood region, and the stable maintenance of the summer monsoon, which directly results in the formation of the flood. One of the major deficiencies in the model is its overestimation of precipitation in the rainfall centers, by about 30%, as compared to the analysis. Another deficiency of the model is the shift northward of the simulated rainbelt near Japan, resulting in a significant bias of rainfall over Japan. In addition, the ending of the flood is not well predicted by the model. Our analysis indicates that a bias pattern in the simulated circulations, which is dependent upon the Earth's surface type (i.e., land or ocean), is possibly the major reason for these deficiencies.