Scale-dependent effects and thresholds in urban climate regulation: The roles of local and surrounding environmental influences

Abstract

Urban green spaces are widely recognized as effective nature-based solutions for mitigating the urban heat island effect. Although previous studies have highlighted the spatial continuity and dynamic characteristics of climate regulation services, most have relied on single-scale assessments, limiting understanding of how environmental characteristics influence urban thermal conditions across spatial extents. This study investigated the effects of local- and neighborhood-scale environmental characteristics on air temperature (T a ) and mean radiant temperature (T mrt ). T a and T mrt at different times of day were simulated using ENVI-met, and generalized additive models were applied to quantify scale-dependent relationships across scales. The relative contributions of environmental variables and the threshold values for effective cooling were subsequently evaluated. The results revealed distinct scale-dependent responses for the two thermal indicators. T a was best explained by neighborhood-scale environmental characteristics within a 200 m buffer, whereas T mrt was most strongly associated with nearby environmental conditions within a 50 m buffer. Neighborhood-scale variables generally contributed more to T a than local variables, whereas daytime T mrt was primarily associated with local tree canopy cover together with neighborhood-scale urban form, reflecting the combined effects of shading and the pedestrian-scale radiation environment. Clustered tree canopy cover showed the strongest cooling effect on Ta, with effective cooling occurring at approximately 10% cover, whereas dispersed canopy required approximately 17% cover to achieve a comparable cooling response. In contrast, T mrt exhibited nonlinear threshold responses to tree canopy cover and floor area ratio. These findings provide references for scale-sensitive urban greening strategies and climate-responsive urban planning and design.