Effects of urbanization and groundwater flow on the subsurface temperature in Osaka, Japan

Subsurface temperatures were analyzed to evaluate the effects of urbanization and groundwater flow in Osaka, the second largest metropolitan in Japan. The temperature–depth profiles were classified into three (recharge, intermediate and discharge) types based on the thermal gradient, shape of the profiles, and temperature itself. The locations of the three types of profiles represent the places of regional and local groundwater flow systems in Osaka plain. The analyses of subsurface temperature using heat conduction–convection theory under the condition of surface warming showed that the depth of minimum temperature in the profile increased with the groundwater recharge rate and time lapse from the beginning of surface warming due to urbanization. Comparisons between observed and estimated temperature profiles showed that the surface warming due to urbanization is larger and occurred earlier in the middle of the city than those in surrounding area, which agreed with the air temperature records.