Hiroyuki Kusaka & Asuka Suzuki-Parker, University of Tsukuba, Tsukuba, Japan

Toshinori Aoyagi, JMA/MRI, Tsukuba, Japan

Sachiho A. Adachi, RIKEN/AICS, Tsukuba, Japan

Yoshiki Yamagata, NIES, TSUKUBA, Japan

Presentation Title: Urban climate projection in Tokyo for the 2050's August by the 4-km horizontal grid spacing RCMs: Impact of RCM and urban scenario




With a population of about 32.5 million, greater Tokyo is the world's largest metropolitan area. Summertime surface air temperatures have been trending upwards by 3.0 K over the last 100 years. Tokyo is already known for its exceedingly uncomfortable summers. In recent years, the number of deaths in Japan caused by heat stroke has been exceeding the deaths from other weather-related disasters including typhoons and tornados. Energy consumption due to an increased urban heat island effect has been a very serious problem since the 2011 Fukushima earthquake. Many citizens are concerned by the degradation of the urban environment and want to mitigate a worsening thermal environment. The influence of urban scenario work and their importance for future urban climate projections has not been sufficiently discussed. This study examined the influence of selected regional climate models (RCMs) and urban scenarios on urban climate projections (UCMs), using two different RCMs coupled with UCMs.

Key Lessons Learned

  • The data distribution system with weather research and forecasting/urban canopy models from the Model for Interdisciplinary Research on Climate (MIROC5) under the RCP4.5 W scenario projected a temperature increase of 2.3 °C.

  • The impact of the ‘urban planning scenario’ is about 0.3 °C for Tokyo, which is comparable to the RCM difference.
  • The ‘compact city scenario’ reduces future warming in suburban areas.
  • Considering the thermal environment, energy conservation and accessibility to the downtown area, the ‘compact city scenario’ is recommended.
  • Mitigating the heat spot at the building-scale (i.e., street level, road surface temperature) will be more effective than heat island mitigation at the urban-scale.

Policy/Practice Implications of Research

  • The examination of the influence of selected regional climate models (RCMs) and urban scenarios on urban climate projections (UCMs) has important implications for mitigation policy targeted towards the future urban climate (micro-climate) in Tokyo and the urban heat island effect (meso-scale).
  • Tools such as the Global Warming Downscaler system web application allows non-specialists to do regional climate projections using a regional climate model; i.e., the simulated results consider impacts of urban planning, land use policy, greening policy and energy saving policy on the future regional climate.

Knowledge Gaps and Needs

  • Coupling RCM and computational fluid dynamics (CFD) models for microclimate projections.
  • Better climate data sets, as impact assessments and adaptation research utilizes future urban climate data created by climatologists.