Comparison of the Impact of Global Climate Changes and Urbanization on Summertime Future Climate in the Tokyo Metropolitan Area

In this study, the impact of global climate change and anticipated urbanization over the next 70 years is estimated with regard to the summertime local climate in the Tokyo metropolitan area (TMA), whose population is already near its peak now. First, five climate projections for the 2070s calculated with the aid of general circulation models (GCMs) are used for dynamical downscaling experiments to evaluate the impact of global climate changes using a regional climate model. Second, the sensitivity of future urbanization until the 2070s is examined assuming a simple developing urban scenario for the TMA. These two sensitivity analyses indicate that the increase in the surface air temperature from the 1990s to the 2070s is about 2.0°C as a result of global climate changes under the A1B scenario in the Intergovernmental Panel on Climate Change’s Special Report on Emissions Scenarios (SRES) and about 0.5°C as a result of urbanization. Considering the current urban heat island intensity (UHII) of 1.0°C, the possible UHII in the future reaches an average of 1.5°C in the TMA. This means that the mitigation of the UHII should be one of the ways to adapt to a local temperature increase caused by changes in the future global climate. In addition, the estimation of temperature increase due to global climate change has an uncertainty of about 2.0°C depending on the GCM projection, suggesting that the local climate should be projected on the basis of multiple GCM projections.