Study on the effect of vertical structure of urban green spaces on microclimate in Guangzhou through a full year numerical simulation

Urban green spaces (UGS) are recognized as effective strategy to regulate microclimates. The vertical structure and size of UGS are both key factors influencing their microclimate regulation capacity. However, in different seasons and under extreme weather conditions such as heatwaves, the cross-effect of vertical structure and size, as well as the impact of energy and water vapor transfer processes within UGS on their microclimate regulation ability, remain largely underexplored. In this study, we developed a thermal environment model and conducted a full year numerical simulation. The results indicate that while UGS generally have a cooling effect, this effect is not always consistent. For instance, during periods of low soil water content, UGS may experience higher air temperatures than residential areas. Within UGS, trees, shrubs, and soils play distinct roles in microclimate regulation. Trees primarily reduce radiation flux through shading, while shrubs and soils contribute to microclimate regulation through ET. Larger UGS generally exhibit a more significant cooling effect, with a clear threshold between size and cooling efficiency, particularly evident in densely vegetated UGS. Furthermore, UGS demonstrates a greater capacity for microclimate regulation during heatwaves. The implementation of irrigation management could further enhance their potential for microclimate regulation. These findings suggest that UGS design and management, including vertical structure and irrigation, should be optimized in urban planning to enhance cooling, especially during extreme heat.