History of Heat Island Phenomenon and its Countermeasures - August 2003 to 2020s

History of Heat Island Phenomenon and its Countermeasures - August 2003 to 2020s

Urbanization over the years has caused the heat island effect in central Tokyo, resulting in a serious rise in temperature. 2003 survey by the Ministry of the Environment showed that the minimum temperature in Otemachi, Chiyoda-ku has risen by about 4 degrees C over the past 100 years, compared to a rise of about 2 degrees C in Yokohama and 2.5 degrees C in Kumagaya, and the rise in temperature in central Tokyo is particularly significant. The temperature rise in Tokyo was found to be particularly significant compared to a rise of about 2°C in Yokohama and about 2.5°C in Kumagaya. This phenomenon is attributed to the density of high-rise buildings, artificial exhaust heat from air conditioners, and an increase in the rate of road pavement.

In order to combat the heat island phenomenon, the Tokyo Metropolitan Government is introducing urban greening and cooled pavement. For example, large-scale expansion of green space has been implemented in Hibiya Park (Chiyoda Ward) and Shinjuku Gyoen (Shinjuku Ward), and it has been confirmed that greening areas absorb heat from the city, resulting in a reduction of approximately 1 to 2 degrees Celsius in the surrounding area throughout the year. At ARK Hills in Minato Ward, rooftop greening has also had the effect of lowering the building's surface temperature by up to approximately 20 degrees Celsius. Low-emissive (Low-E) glass is used for the building windows, and it has been proven to reduce the cooling load by up to 15%. In addition, insulation materials developed by Shimizu Corporation have been introduced into buildings in central Tokyo, and have proven effective in lowering the temperature of exterior walls by approximately 1.5 degrees Celsius.

In the 2020s, measures to combat the heat island effect in central Tokyo are also being strengthened. 3.5 hectares of green space have been installed on the Shinagawa Season Terrace site by NTT Urban Development, with the effect of reducing ambient temperatures by an average of 1 to 1.5 degrees Celsius. In addition, high reflectance paint is used on the exterior walls of the building, reducing surface temperatures by up to 10 degrees C and lowering ambient temperatures by approximately 1 to 2 degrees C.

As a countermeasure for roads, water-retaining pavement has been introduced, which has been shown to reduce road surface temperatures by approximately 10°C compared to ordinary asphalt pavement. This thermal barrier pavement has been adopted on major arterial roads in Tokyo and on the Tokyo Outer Ring Road (Metropolitan Expressway Route C2), and is effectively functioning to reduce temperature rises in urban areas.

These measures are being promoted in collaboration with the Japan Weather Association, Shimizu Corporation, and Tokyo Gas, and are being continued with quantitative analysis of temperature reduction effects in each region. The policy is to maintain a sustainable urban environment through a variety of technologies and initiatives.