Quantifying the Net Thermal Effects and Inequalities of Spatiotemporal Evolution of Building–Greenspace Coupling

The cooling ecosystem services provided by urban greening are fundamental to climate adaptation, yet they are compromised by urbanization that alters the spatial configuration between vegetation and buildings. The spatiotemporal dynamics linking this evolving building–greenspace coupling to thermal environment and equity remain poorly understood. This research develops a novel remote sensing–based analytical framework integrating a new building–greenspace coupling index (BGCI) within a modified difference-in-differences model to quantify the net effect of urban form evolution on land surface temperature (LST) in the Xiamen–Zhangzhou–Quanzhou (XZQ) metropolitan area (2012 to 2023). Results reveal a near-linear positive association (R² = 0.93) between the BGCI and LST, amplified in densely populated areas. Quantitatively, a 0.1-unit increase in the BGCI corresponds to an approximate 0.28 °C rise in mean LST. Furthermore, LST inequality analysis indicates disparities across urban functional zones are the primary source of thermal heterogeneity. An increase of 0.09 in the BGCI is associated with a 0.39 rise in the inequality index of LST changes. This study offers a quantitative methodology for assessing the thermal performance and equity implications of urban spatial transformations. The findings provide geospatial evidence to optimize land use for mitigating urban heat and enhancing thermal equity.