In this investigation, a numerical model expressing advection and diffusion effects is used to examine air temperature rise in urban areas that are on the leeward side of green areas. The model results are then verified by comparison with measurement results. When the measurement point is at a distance of 30 m or more from a green area, the air temperature of the urban area is not affected by the green area. An isotropic diffusion model and a model incorporating buoyancy were applied for the vertical diffusion term. Results of air temperature rise with distance from the green area were compared for both calculated and measured values. The rise in air temperature due to the development of the urban boundary layer in the area near a green space is expressed using the sensible heat flux from the ground surface, the distance from the green area and the wind velocity. We considered an approximation of air temperature rise in order to express the following situation: when entering the urban area, air temperature rises sharply, and when reaching a certain distance from a green area, it becomes almost constant.