Spatial Decay Structure and Seasonal Variation of Shoreline-Mediated Cooling in a High-Density Urban Environment

Urban water–vegetation systems play an important role in mitigating surface heat, yet the spatial decay structure of shoreline-mediated cooling remains insufficiently quantified in high-density urban environments. Focusing on seven urban water bodies within the heritage buffer zone of the Beijing Central Axis, this study combines 120 m shoreline segmentation with 0–600 m ring-buffer analysis to examine seasonal shoreline cooling patterns using Landsat-derived land surface temperature (LST) and Sentinel-2 vegetation information. The results show that shoreline cooling followed a layered spatial decay structure rather than a single fixed-distance effect. The most rapid LST increase generally occurred within the first 200 m from the shoreline, forming a nearshore rapid-gradient zone, while cooling distance (CD) represented a broader outward reach of detectable cooling. Cooling intensity (CI) was strongest in summer, whereas the seasonal differentiation of CD was weaker than that of CI. Vegetation greenness was generally negatively associated with LST, especially in the near and middle shoreline zones, and this relationship was supported by the same-date Landsat NDVI robustness test. After controlling for built-up intensity and waterbody-specific differences, shoreline distance, vegetation greenness, and built-up intensity mainly operated as additive spatial predictors of LST, while the NDVI × Distance interaction provided limited additional explanatory power. These findings suggest that shoreline cooling in high-density heritage urban areas should be understood as a spatially differentiated interface process, and that planning should prioritize the nearshore rapid-gradient zone while managing the broader shoreline transition area according to local vegetation and built-up conditions.