A study of street trees and their effects on pedestrians’ perceptions during summer

Poor thermal and light climates can have significant negative effects on human living qualities. Exploring sustainable ways to address these issues is an urgent task, and at the street level, trees pose a potential solution. This study aimed to determine the effect of street trees on pedestrians' physiological comfort under different conditions. This was accomplished by field surveys, including questionnaires distributed at several forested streets in the Qingbaijiang District (QBD), a suburban area of Chengdu, China. Data analysis showed that people had different responses towards either physical or meteorological factors. They responded differently to various environmental factors, and the responses varied over physical and meteorological contexts. It was found that pedestrians' neutral temperature and lighting levels were 28.64 °C, as indicated by physiologically equivalent temperature (PET, °C), and 0.91 klx, as indicated by illumination (klx). The percentage of people in favor of larger tree crowns increased considerably for PET (from 60 % at 30 °C to 90 % at 45 °C) and illumination (from 30 % at 0 klx to 100 % at 20 klx) elevations under small-sized trees. People preferred larger crowns and shorter trunks as they made them more comfortable. Their responses were also different for various PETs and daily periods. This is evident from the change in either thermal sensation vote (TSV) or overall comfort vote (OCV). The increase of either PET or illumination might result in TSV increase and OCV decrease. In relative terms, tree crown sizes (diameter, TCD) had a significant influence on pedestrians' comfort. Increasing TCD by 1 m resulted in a TSV reduction of 0.449 and/or an OCV increase of 0.475 (sig. < 0.001). Results from this study may aid in future urban design and forestation works with the goal of improving pedestrians' comfort.