Improvement of Extreme Precipitation Simulation over Korea Using a Regional Climate Model: Impact of Model Resolution and Urbanization

Abstract

Recently, precipitation extremes have been increasing ever due to global warming, so it is essential to produce more accurate climate change scenarios to reduce huge damages. Various application studies are being conducted using the climate change scenarios produced by the CORDEX to become the basis of policy decisions. However, when analyzing the CORDEX data results, the model performance for extreme precipitation is still low. In this study, the causes that the low performance for extreme precipitation simulation are assumed to be 1) the coarse model resolution and 2) the absence of the coupling to the urban model. The effects of the model resolution and urbanization on precipitation simulation were examined using the WRF model to confirm the assumptions above. When conducting the high-resolution experiment, extreme precipitation on the Korean Peninsula was improved. As the model resolution is increased, small-scale waves such as meso-β scale or meso-γ scale waves can be further decomposed. Hence the precipitation generated by the small-scale waves can be further increased. The increased resolution also amplified the spatial variation of the topographic height, reflecting more detailed terrain. As a result, the more robust mountain-plain solenoid simulations induce the increased daytime precipitation in the mountainous ranges and the decreased nighttime precipitation over the plain. The influence of urban parameters (the anthropogenic heat and the building height) on precipitation simulations were analyzed using the WRF with the single-layer urban canopy model. The higher values of urban parameters intensify the mean and extreme precipitation around the Seoul metropolitan areas, improving model performances. The anthropogenic heat increases the daytime precipitation, and the building height increases the nighttime precipitation. Both parameters change the sensible heat flux inducing the surface temperature changes, which resulted in precipitation changes by CC-relationship. However, these parameters change the precipitation amplitude but cannot improve the diurnal variations of precipitation. When producing the next generation of CORDEX climate change scenarios, it is proposed to use a high-resolution regional climate model coupled with the urban model to improve precipitation simulations.