Multiscale estimation of the cooling effect of urban greenspace in subtropical and tropical cities

Abstract

Urban greenspace has been widely recognized for its beneficial role in mitigating the urban heat island (UHI) effect and enhancing human thermal comfort. However, understanding on the thermal effects of greenspace still remains limited, particularly in the areas of regional differences, scale issues, and modeling approaches. This study employs a multiscale approach to evaluate the cooling effect of greenspace in Hong Kong and Singapore by combining remote sensing techniques at the territory level, a hybrid modeling approach at the urban district level, and field measurements at the micro level. Results demonstrate that the approach generally performed well in evaluating the relationship between cooling effect and various explanatory variables. At the city scale, the average reduction in LST by greenspace ($△{\mathrm{LST}}_{G-\mathrm{UF}}$) was found to be 3.08 $℃$ in Hong Kong and 2.84 $℃$ in Singapore, respectively. However, the cooling effect of greenspace is much reduced at the urban district level. Of the evaluated urban districts, greenspace was found to have a LST reduction effect ranging from 0.27 to 1.56 $℃$ in Hong Kong and from −0.02–2.69 $℃$ in Singapore, respectively. At the micro level, the study reveals that building height and greenspace volume have the most significant influence on ambient temperature variations during the hottest time of the summer season. These findings not only highlight the importance of considering scale and time variations when evaluating the thermal effects of greenspace but also help identify effective greenspace deployment strategies to combat excessive urban heat.