Study of the relationship between the spatial structure and thermal comfort of a pure forest with four distinct seasons at the microscale level

Abstract

The local thermal environment of forest green space has a great influence on users' experience and health. Thus, it is of great value to systematically study the relationship between forest spatial structure and thermal comfort at the microscale. This study examined the relationship between the spatial structure and thermal comfort of bamboo forest using a case study of "Zhu Hai Dong Tian" Park in Dujiangyan city, Sichuan Province, China. We selected 20 in-forest study sites and three out-of-forest control sites and measured 13 spatial structure parameters and five climatic parameters (air temperature, relative humidity, wind velocity, surface temperature and global radiation) at the 23 sites for three representative days in each season. Then, the five climate parameters, human body parameters (sex, age, height, weight, clothing, and activity), and sky view factor (SVF) were input into Rayman software to calculate the physiological equivalent temperature (PET) value of each site in each season. PET is the physiological temperature value of the equivalent thermal environment based on energy balance. In this study, PET values between 15 and 22 °C indicated that the thermal environment was comfortable. The results showed that the PET values of the 20 study sites in the bamboo forest were mostly at a comfortable level in spring and autumn but had various degrees of heat stress and cold stress in summer and winter, respectively. The relationship between microstructure parameters and PET in four seasons was expressed by four models. In the spring and summer models, CPR (cover plant ratio) and CDW (canopy diameter width) were positively correlated with PET and had the greatest influence. In the autumn and winter models, DFS (degree of facing the sun's trajectory vertically) and CPR were positively correlated with PET and had the greatest influence. In addition, DBH (diameter at breast height), DB (density of bamboo forest), S (slope), CPH (cover plant height), ST (slope of the trunk), SP (spacing), H (height of the space), and IL (internodal length) were included in the models of all four seasons. The research results provide useful information for improving the thermal comfort of microscale pure forest space by modifying the forest structure. The results can be used to guide forest management to further create forest space that integrates climate comfort, landscape, and service.