Cooling Potential of Urban Green Spaces in Summer

Abstract

The urban heat island phenomenon has recently become a serious subject of public concern. This chapter aims to clarify the cooling potential of urban green spaces in summer. At first, it shows that green space and anthropogenic heat emission have a great effect on the temperature in downtown areas from the various data collected from 27 observation points in Minato-ku, Tokyo. Then, it clarifies the cooling potential of green spaces. The results of multiple regression analysis, using the mean daily maximum temperatures in August as dependent variables and the size of woodland area and the amount of anthropogenic heat emissions as explanatory variables, showed that an increase in trees contributes to a reduction in temperature in urban areas, and that an increase in the amount of anthropogenic heat emissions causes a rise in temperature. A multiple regression model in equations and a coefficient of correlation among mean daily maximum temperature, woodland area, and amount of anthropogenic heat emissions were obtained as follows: Y = 32.0011 − 0.001(X 1) + 0.0033(X 2), r = 0.7276, where Y = the mean daily maximum temperature, X 1 = woodland area, and X 2 = the amount of anthropogenic heat emissions. From this regression analysis, it can be said that the cooling influence by green spaces of 22,500 m2 is equivalent to the heating influence by the anthropogenic heat released from 70 offices of average size in Minato-ku, having a total floor area of about 211,726 m2. Furthermore, the cooling potential of a green space of 22,500 m2 during July to September can be expected to reduce about 236 times as much carbon dioxide as the same green space absorbs for 1 year. In conclusion, green spaces in urban downtown areas have the function of air conditioning provided by nature.