Observed and simulated impacts of anthropogenic heat on air temperatures in downtown Tokyo and Osaka

This study investigates actual impacts of anthropogenic heat on urban surface air temperatures through observations and simulations. For this purpose, summer field campaigns were conducted during August 2007 in Tokyo and Osaka, Japan. The surface meteorological observations using the multi-site installed instruments were carried out in two couples of urban areas in Tokyo and Osaka. Each couple consists of an uptown low-rise residential area and a downtown high-rise business area within the same city. Those areas were contrastive in both terms of canopy structure and anthropogenic heat level. The amounts of anthropogenic heat were estimated based on actual energy consumptions in each area, indicating greater value up to 200W/m2 in business areas and less value around 20W/m2 in residential areas. Anthropogenic heat in business areas also indicated large decreases by around 50% at weekends compared to those on weekdays. Then, differences in areal mean surface air temperatures between business area and residential area were analyzed for weekdays and weekends separately. As a result, greater differences up to 1 °C were found on weekdays compared to those on weekends both in Tokyo and Osaka suggesting actual impacts of anthropogenic heat on air temperatures in downtown business areas. To verify this point, Weather Research and Forecasting model (WRF) was applied to Tokyo and Osaka. Our original urban Canopy and Building energy Model (AIST-CBM) was incorporated into WRF for the consideration of dynamic and thermodynamic effects of urban canopy and anthropogenic heating. Finally, WRF/AIST-CBM coupled model was found to reproduce the observed impacts of anthropogenic heat on air temperatures in downtown Tokyo and Osaka.