Regional climate simulation of the 1998 summer flood over East Asia

In this study, the severe flood case over East Asia during the 1998 summer was simulated using a regional climate model (SNURCM) with 60 km horizontal resolution (EX60), and the model performance in reproducing the extreme climate events was evaluated. An experiment with higher horizontal resolution of 20 km (EX20) was also performed in order to assess the impact of increased resolution on precipitation simulation of the severe flood. The model reproduced the severe precipitation events occurring in central China in June. In EX60, the temporal and spatial variations of the abnormal Meiyu monsoon fronts, which were well observed were also simulated reasonably except in southern China. The area-averaged daily precipitation and surface air temperatures were underestimated, but their temporal evolutions were in good agreement with observation. In the higher resolution experiment (EX20), simulated downward solar radiation, latent heat flux and convective rain were increased in the major severe rain area over the Yangtze River Basin. The increased precipitation in EX20, which was attributed mainly to the increase of convective rain, resulted in the enhanced precipitation intensity, but only slightly affected total precipitation amounts. The improvement in the higher horizontal resolution simulation appeared in precipitation resulting, in particular, from increased convective activity due to increased latent heat flux at the surface. Nevertheless, the model had significant precipitation bias in some areas with disagreement between the simulated precipitation patterns and distribution, and the observations. The model also had surface air temperature bias resulting from cold biases of the land surface model. With horizontal resolution increased to 20 km, the convective and non-convective precipitation was increased for the late afternoon and early evening time, increasing the total precipitation slightly.