Vertical contrast of trees and buildings determines urban land surface temperature

Urban trees serve as vital nature-based solutions for improving thermal sustainability and livability. While many studies have examined the effects of urban trees on temperature given their horizontal distribution, the effects of their vertical structure, especially in relation to surrounding buildings, remain underexplored. To address this knowledge gap, this study investigates the influence of tree height on land surface temperature (LST) during summer across 305 Chinese cities, using high-resolution datasets on tree cover and their vertical structures. The results reveal a similar magnitude of tree height on LST to the effect of horizontal canopy coverage variations. At a given tree cover level, increasing tree height initially elevates LST but eventually leads to cooling as tree height continues to rise. This reversal of covariation between LST and tree height stems from two competing processes—warming due to increased shortwave radiation capture as tree height rises vs. cooling from enhanced evapotranspiration. The critical threshold, where cooling outweighs warming, is observed at a median tree height of 4.3 m below surrounding buildings. The cooling effect is more significant in regions south of 30°N. These findings highlight the importance of accounting for vertical interactions between urban trees and buildings to enhance our understanding of their combined effects on thermal environment.