Effects of Tree Arrangement and Leaf Area Index on the Thermal Comfort of Outdoor Children’s Activity Space in Hot-Humid Areas

Hot-humid areas have long, hot summers and poor outdoor thermal comfort (OTC). The urban heat island (UHI) effect exacerbates the deterioration of OTC in hot-humid areas, seriously affecting the thermal safety of children’s outdoor activities. In this study, 60 scenes were simulated using ENVI-met based on different leaf area index (LAI) and planting arrangements to explore how tree LAI and planting arrangements affect the small-scale thermal environment during hot summer months and to assess OTC using the Universal Thermal Climate Index (UTCI). The research shows that (1) high LAI trees optimize OTC more than low LAI trees, but low LAI trees can be planted multiple times to achieve the level of optimization of high LAI trees; (2) increasing the number of trees optimizes the OTC of the study area, reducing the UTCI by up to 3.7 °C with increased planting compared to unshaded areas; (3) thickening the shade in the east–west direction optimizes the OTC of the study area more than thickening the shade in the north–south direction, with too much north–south shade optimizing the OTC of the study area by only 0.01%. This study provides practical advice for the design of planting in outdoor CAS in hot-humid areas.