The purpose of this study is to analyze the characteristics of a thermal environment in a substantial urban area by numerical simulation. First, we proposed a method for the gathering of spatial geometry and material data in a substantial urban area and developed a 3D CAD model, which was sufficiently accurate for the calculation of heat transmission. Then, we calculated the surface temperature for every urban block by using the numerical simulation on the assumption of a clear sky day in summer in Tokyo. Further, we ascertained the Heat Island Potential (HIP) for every urban block, which was an index of the sensible heat flow rate on all surfaces. The results indicated that the variation in HIP of 36 urban blocks were large not only in the day but also in the night. Furthermore, it was shown that every block group classified by land use type exhibited a characteristic tendency of the diurnal change in HIP, and that the varied land cover resulted in the differences in HIP in the same land use type group.
