Future change of wintertime urban heat island intensity over Japan

Abstract:

Urban canopy process is essential to investigate thermal environment in the near future, because surface air temperature (SAT) increase due to urban heat island is comparable to the one due to the global climate change over major metropolitan areas in Japan. During the past 100 years, mean SAT increased about 3 ºC in Tokyo, and 2 ºC in Nagoya and Osaka, while world mean SAT increased only 0.66 ºC. Major reason of difference in the warming is effect of the urban heat island (UHI), whose intensity also increased during the period and often the most during winter. This study investigates change in UHI intensity (UHII) of major metropolitan areas (Tokyo, Nagoya, and Osaka) in Japan by effects of the global climate change. A series of climate simulations performed. Present climate simulations with and without urban process are conducted using a high-resolution numerical climate model, the Weather Research and Forecasting (WRF) model. Future climate projections with and without urban process are also conducted. The future projections are performed using the pseudo global warming method, assuming lateral and bottom boundary conditions in the 2050s estimated by a GCM under the RCP 8.5 scenario. Simulation results indicated that UHII would be enhanced more than 30% in Tokyo during the night due to the global climate change.