Impacts of Tree Canopy Cover on Microclimate and Human Thermal Comfort in a Shallow Street Canyon in Wuhan, China

Abstract

Increasing the number of street trees can be a promising method to reduce impacts of climate change currently impacting urban public health. However, the quantitative relationships between tree canopy cover and thermal comfort remains unclear, particularly in areas with high temperature and high humidity. This study aims to provide a better understanding of the effects of different degrees of tree canopy cover on human thermal comfort in shallow street canyons in a high temperature, high humidity area of China. Microclimatic measurements and qualitative surveys were conducted on sunny summer days in a shallow street canyon in Wuhan. The results suggest that microclimate benefits are greater for areas with a high-percentage tree canopy cover compared to medium- and low-percentage tree canopy cover—especially at noon. In streets with a high-percentage tree canopy cover, afternoon air temperatures and mean radiant temperatures can be reduced by up to 3.3 °C and 13.9 °C, respectively, compared to a similar street with no tree shade. The thermal sensation prediction formula is proposed and the relationship between human thermal sensation and microclimate factors is established. Blocking solar radiation and increasing wind speed are more feasible than controlling air temperature and humidity as ways to improve human thermal comfort.

Keywords

• tree canopy cover
• mean radiant temperature
• thermal comfort
• thermal sensation
• physiologically equivalent temperature
• street canyon