How to quantify the cooling effects of green infrastructure strategies from a spatio-temporal perspective: Experience from a parametric study

Urban green infrastructures (GI) are efficient nature-based solutions for urban heat mitigation. Typically, three GI typologies, i.e., green roof, green wall, and street tree, are often recommended and implemented for outdoor thermal comfort modification and passive energy saving. However, the current evaluation of the cooling effects for GI strategies is not comprehensive for two reasons: 1) lacking a holistic assessment to involve different combinations of GI typologies; 2) lacking a spatio-temporal lens to quantify the cooling effects. This study proposes a systematic approach to quantify the cooling effects of GI strategies from a spatio-temporal perspective. Through a parametric study in ENVI-met model, the cooling effect of seven GI strategies were quantified, and different street orientations and sky view factor (SVF) were also involved. Three cooling indicators were proposed for different sustainable planning targets: cooling intensity (CI), cooling area (CA), and cooling duration (CD). The results showed that the seven GI strategies performed differently under various urban morphologies. The greatest cooling effect of GI strategies was observed at SVF = 0.7, after which additional strategies may be needed for urban heat mitigation. Three proposed indicators were found to show similar patterns across the GI strategies, but revealed the details of cooling effects differently. Overall, this study represents the first assessment of the cooling effects of seven GI strategies across different morphological settings. The evidence-based understanding contributed by this study can help planners and designers to optimize the thermal environment in subtropical climate. The systematic approach from a spatio-temporal lens can be transferred to other cities and climate backgrounds.