Quantitative Evaluation of Urban Heat Island Mitigation Effect and Reduction Human Heat Stress by Large Greening of Roof

Abstract

The actual condition of occurrence of heat island and the cooling effect to heat stress in the central urban area by the large roof greening building (ACROS Fukuoka) were investigated in Fukuoka city area which is the largest city of Kyushu region. The operative temperature which is the heat energy that a human body receives from the surrounding environment by heat conduction and radiation was calculated by using meteorology data acquired on the city area in summer at 2007. The heat stress index (HSI) was defined a human body temperature that a standard adult man had to cool by perspiration when he was standing during 10 minute as index of heat stress in the city area. A decreasing effect for operative temperature by sun shade of typical urban tree Zelkova was estimated from 5.7 to 7.2 degree-C. The operative temperature would be increased 4.10 degree-C and 0.64 degree-C, respectively, if the air temperature or the ground surface temperature was 5 degree-C higher under the weather condition of August-1 2007 at the roof floor of ACROS Fukuoka. A breeze, however, has an operative temperature decreased remarkably, so the heat stress would be eased. The HSI would reduce 0.26 and 0.14 degree-C, respectively, under sun light or sun shade condition, if the wind speed is 5.4 ms-1. As a result of a comparison of a ratio of radiation energy input to increased air temperature from early morning to noon, it was estimated that an increasing air temperature on ACROS greening garden was reduced about 70%- 73% of the central urban area. The operative temperature and HSI would be risen about 4.2%-6.9% and 7.6%-11.8%, respectively, if the building is a non-greening building, we concluded. © 2008, The Society of Agricultural Meteorology of Japan. All rights reserved.