Recently, localized heavy rainfalls over heavily urbanized areas have caused severe damage in Japan. On 5 August 2008, a localized heavy rainfall caused a rapid increase in drainpipe discharge, which killed five people working in a drainpipe near Zoshigaya, Tokyo. This study investigated the effect of actual land surface initial state on this localized heavy rainfall by two ensemble experiments using a cloud-resolving model that included precise urban features. The first experiment (ACTD) considered realistic initial land surface state derived from off-line land surface model calculation using meteorological observation provided by Japan Meteorological Agency. In the second experiment (CTRL), the initial soil moisture was set to homogeneously wet condition, and the initial land surface temperature was set to the same value as near surface air temperature. The amount of rainfall was significantly increased and close in the observed value over Tokyo at the beginning of rainfall in the ACTD experiment. The larger land surface temperature over urban area and larger soil moisture over surrounding area caused stronger contrast of surface heating in ACTD experiment. The contrast of surface heating caused the contrast of near-surface air temperature and intensified the convergence of horizontal wind and updraft over the urban area, and resulted in the larger amount of rainfall at the beginning of rainfall.
