Synergistic effects and impact pathways of urban blue-green space on local thermal environment: A case study in Shanghai

The cooling and humidifying effects of urban blue-green space (UBGs) have been widely recognized as the nature-based solutions (NbS) for improving urban thermal comfort. However, the synergistic effects and impact pathways of water bodies and green spaces on urban thermal environment have not been thoroughly explored. Here, by integrating meteorological factors (MFs) data and GF-2 images in Shanghai, China, we comprehensively investigated the synergistic effects and impact pathways of UBGs on MFs and physiological equivalent temperature (PET) through generalized additive models (GAM) and structural equation models (SEM). The results demonstrated that air temperature (Ta) exhibited a stronger correlation with the distribution of UBGs at larger scales than relative humidity (Rh) did. In contrast, Rh was primarily influenced by adjacent UBGs within an 80 m buffer. The synergistic effects of UBGs on MFs exhibited nonlinear characteristics, which were dependent on specific threshold ranges of UBGs parameters. Consequently, increasing UBGs does not necessarily enhance cooling or humidifying effects. In addition, the influence of UBGs on MFs was scale-dependent. This scale dependency resulted in distinct dominant pathways through UBGs patterns-MFs variations-PET distributions. Specifically, at the 80 m buffer scale, UBGs significantly affected Rh, but its indirect effect on PET was limited and non-significant. While at the 1500 m scale, Ta modulation emerged as the dominant pathway, as evidenced by its higher path coefficients. These findings are essential for further understanding the synergistic effects and impact pathways of UBGs on MFs and thermal comfort, as well as providing actionable insights for climate-adaptive UBGs planning.