Tree form characteristics as criteria for tree species selection to improve pedestrian thermal comfort in street canyons: Case study of a humid subtropical city

The combined effect of tree characteristics on heat stress in different street canyons has been widely reported. However, there remains a lack of effective methods for improving pedestrian thermal comfort through the use of integrated knowledge of tree characteristics. Here, a tree species selection approach was developed for assessing the dynamic effects of tree forms and canyon geometries on pedestrian thermal comfort to address the issue of the right tree in the right street canyon. The leaf area density (LAD), crown diameter (CD), tree height (HT), and trunk height (TH) were used as criteria for determining tree species characteristics, and the weighted outdoor thermal comfort autonomy (OTCAw) was adopted as a quantitative index of thermal comfort variation over time. In a case study of Wuhan, China, we evaluated the thermal comfort enhancement potential of 45 tree forms in street canyons with varying aspect ratios and orientations from 7:00 to 21:00 by using a validated ENVI-met model. Accordingly, tree pruning strategies and 19 optimal tree forms were proposed for corresponding street canyons. Our study provides insight into the optimal street tree species for minimizing heat exposure of pedestrians under various urban canyon configurations.