The Effects of Topography and Sea Surface Temperature Anomaly on Heavy Rainfall Induced by Typhoon Chaba (2016)

Abstract

Typhoon Chaba (2016) made landfall on the Korean peninsula and caused record-breaking rainfall in southeastern Korea. In particular, Ulsan metropolitan region experienced a 300-year flood due to 319 mm of rain for 3 hours. The reasons for heavy rainfall induced by typhoon Chaba were possibly associated with mountainous topography in southeastern Korea and warm sea surface temperature (SST) anomaly in the East China Sea. In this study, we investigated the effects of topography and SST anomaly through numerical experiments with high-resolution Weather Research and Forecasting (WRF) model. To verify the topographic effect in southeastern Korea, we set 3 nested domains with horizontal grid spacings of 9-3-1km and conducted the control experiment (CTL) and the reduced topography experiment (TOPO). As a result, the CTL experiment simulated more rainfall on the windward side due to the lifting effect by mountain compared to the TOPO experiment. The air flow in the CTL experiment was mechanically lifted by mountain slopes, and the orographic lifting enhanced precipitation on the windward side. We also conducted the experiment with climatology sea surface temperature in the East China Sea (CSST) to examine the effect of SST anomaly on typhoon-induced precipitation. The CSST experiment simulated less heavy rainfall compared with the CTL experiment because cold climatological SST in the East China Sea led to decreased TC intensity and at landfall time. Therefore, the numerical experiments indicated that heavy rainfall in Korea induced by typhoon Chaba could be enhanced by the effects of intrinsic topography in southeastern Korea as well as warm SST anomaly in the East China Sea.