Moisture transportation by local circulation is examined during calm summer days at Kanto plain using meso-scale numerical model, in order to clarify an urban effect on the distribution of water vapor in the urban boundary layer. The numerical results show that the vertical velocity at sea breeze head is enhanced when sea breeze and thermal convection are combined in urban area near Tokyo. Because the combined updraft strongly lifts surrounding surface humid air, precipitable water vapor is increased around the urban area. CAPE indicates a little bit of decrease in atmospheric stability in the urban area on calm summer days.
