Urban impacts on deep convection development in the Seoul metropolitan area: A case modeling study of a scattered convective precipitation event

Abstract Storms causing urban precipitation can develop from interactions between various local forcings in and around cities. This study investigates urban impacts on storm development and precipitation and their interactions with topographic impacts for a scattered convective shower event in the Seoul metropolitan area (SMA), South Korea. For this, ensemble simulations with land use map and topography of the SMA and additional sets of ensemble simulations in which the urban area, urban heating, urban drag, or topography in the SMA is removed are conducted using the Weather Research and Forecasting model. The precipitation amount in Seoul for this event substantially increases by urban impacts. This precipitation increase is mainly attributed to the urban heat island (UHI) which helps convective cells develop into strong storms by increasing the temperature gradient at the front of cold outflows and enhancing updrafts there. Although weak urban breeze is induced by the UHI, it does not play crucial roles in precipitation for this event. Meanwhile, the urban drag causes marginal changes in precipitation amount but delays precipitation evolution by about 1 hour. The interaction of topographic impacts with urban impacts also contributes to the development of strong storms in Seoul and increases precipitation in northeastern Seoul. This is attributed to the circulation induced by convection over the eastern mountains which suppresses precipitation development near the western coast by sea breeze in the morning and preserves the warm air. The preserved warm air later moves into Seoul along with the sea breeze and invigorates storm development in Seoul in the late afternoon.