Investigating Thermal Variations in the Adjacent Space of Trees in a Subtropical Zone: From Mobile Measurements and ENVI-met Simulations

Abstract: Urban trees are widely regarded as effective solutions for mitigating microclimate. While many studies have explored the cooling benefits of trees, fewer focused on the spatiotemporal characteristics of their thermal effects on adjacent spaces, particularly in urban squares where design and land constraints restrict extensive tree planting. In Guangzhou, China, this study first analyzed how a single tree influences energy components and microclimate variations in its adjacent space, considering dynamic shading effects. Subsequently, using a validated ENVI-met model, we assessed PET (physiological equivalent temperature) variations under and around trees in 36 line-planting scenarios within an urban square. Results showed that tree shading reduced PET by up to 4.7 °C, extending cooling to surrounding areas, which experienced an additional 1.1 °C reduction in the afternoon compared to the area directly beneath the tree. In shading areas,  Qh (sensible heat flux) was mainly driven by negative Qs (heat storage) from the underlying surface. Tall trees with high canopies provided limited cooling directly beneath but were effective in adjacent spaces during morning and afternoon hours. Furthermore, cooling benefits exhibited threshold effects and interacted with prevailing wind and solar radiation. These findings improve understanding of urban trees’ thermal effects and offer design recommendations for urban squares and similar open spaces to maximize cooling potential.

Keywords: Urban trees; Tree shading; Urban squares; Energy balance; Microclimate; ENVI-met