Water Vapor Distribution in an Urban District using Three-dimensional Urban Geometry Model Under Sea Breeze Event

Regarding the actual conditions of the heat environment within urban city blocks, mobile meteorological observations in a residential area of Tokyo have pointed out the need to properly understand the dynamics of water vapor content on a city block scale due to significant WBGT fluctuations even within a few kilometers of observation routes. In this study, tracer flow analysis using LBM based on a detailed three-dimensional urban model assuming sea breeze inflow was conducted in order to understand the characteristics of water vapor distribution within a city block. As a result, it was found that the water vapor distribution in the city block is characterized by the distribution of water vapor inflow from the sea area due to sea breezes. The area with low water vapor was located on the leeward side of the high-rise buildings, where the sea breeze was blocked by the buildings and water vapor originating from the sea did not easily flow into the area. It was also found that the advection pattern of water vapor changed depending on the location of the main flow direction and the arrangement of the city block structures. Although we confirmed that the above distributions are generally consistent with the water vapor distributions measured by the mobile observations, there are also some difference from the observation result. This is expected to be evapo-transpiration from water bodies and vegetation which are not considered in the numerical model.