Urban effect on an local convective rainfall over Seoul Metropolitan area

We examined the performance of Weather Research and Forecasting (WRF) model to simulate a local convective rainfall event over Seoul Metropolitan area (SMA) on 6 July, 2017. The surface weather chart shows that SMA is located on the edge of high pressure system on the selected day. The CAPE at Osan which is the nearest sounding station is 1979 J kg^-1 prior to the precipitation event. The rainfall started at 1600 LST and ended at 2100 LST over SMA but intense rainfall occurred from 1700 LST to 1900 LST. The penetrating sea breeze and rural breeze converge in the eastern part of SMA, resulting in rainfall. This suggests that good simulation of local wind such as sea breeze and rural breeze is important for accurate prediction of rainfall over urban area. The comparison of rainfall amount between simulation (CNTL) and observation showed that model captures intensity and location of the maximum rainfall over SMA, reasonably. To understand the urban effect on the rainfall event, we performed two sensitivity tests. The first one (SENS1) is the run with no anthropogenic heat and the second one (SENS2) is the run with no anthropogenic heat and low roughness over urban area. Compared to CNTL, maximum rainfall amount over SMA decreased significantly in both sensitivity runs with smallest rainfall amount in SENS1 and location of maximum rainfall also moves to the southeast. This suggests that urban effect of anthropogenic heat and large roughness contributes to increase of concentrated rainfall amount and also plays a role in determining its location over urban area.