Japan Meteorological Agency Identifies Heat-Island Effects Using New Model

The Japan Meteorological Agency (JMA) released on July 9, 2012, the results of its analysis of the heat-island effects seen in urban areas in Japan using a new urban climate model that takes into account the effects of anthropogenic exhaust heat from driving cars, operating air conditioners, or ground conditions in urban areas. Because of the heat-island effect, temperatures in urban areas rise higher than in other areas.

It's been found that the average temperatures in Tokyo, Osaka, and Nagoya have risen by about three degrees Celsius through the last 100 years, caused by not only global warming but also heat-island effects in urban areas. JMA developed a new model dedicated to the urban climate concerning the effects of clouds and precipitation, ground conditions, buildings, and anthropogenic exhaust heat, and conducted its first quantitative evaluation of heat-island effects as manifested themselves in monthly mean climatology. Simulating the air temperature variations during one month in the central areas in Tokyo, Osaka, and Nagoya in August 2011 provided the conclusion that these heat-island effects caused a one-to-two degrees Celsius increase in temperature.

The results of the analysis also show that in the urban areas the increase ratio of the lowest temperature of a day is larger than the highest temperature, because nocturnal radiation cooling is inhibited by structures like buildings. Moreover, the results show that relative humidity in urban areas has been lowered for a long time span by the effects of lowered moisture of the ground surfaces covered with man-made materials and also higher temperatures.

Related JFS article:
[Newsletter] Efforts in Japan to Mitigate the Urban Heat Island Effect

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