Associate Professor Fudan University Shanghai, China (People's Republic)
Numerous studies have explored the cooling effect of greening due to evapotranspiration, enhanced albedo, and interception of shortwave radiation to reduce the air temperature in residential quarters (RQs). However, few studies have considered the tree canopy coverage (TCC) threshold, particularly considering human thermal comfort and heat dynamic processes simultaneously. Therefore, in this study, we selected three typical RQs in Nanjing with different building heights and densities, and used both in-situ measurements and ENVI-met–based numerical models to simulate scenarios with different TCCs. The results showed that the amount of temperature reduction caused by trees did not continuously increase with increasing TCC. In addition, the benefit of trees on human thermal sensation was more obvious in the RQs with relatively low-rise buildings, while trees in RQs with high-rise buildings can hardly relieve human thermal discomfort. Considering both heat dynamics and human thermal comfort, this study quantitatively determined that the maximum effective TCC thresholds of RQs with heights of 33 m (11 floors), 54 m (18 floors), and 100 m (33 floors) were 45%, 30%, and 25%, respectively. Hence, we recommend that not only the provisions on greenspace areas, but also a standard for the maximum TCC threshold, should be set in relative regulations. The findings of this study have important implications for climate-resilience planning and design, especially at the neighbourhood scale.
