Construction and Optimization of an Integrated Cold Island–Habitat Quality Network: Evidence from a Subtropical Megacity

Rapid urbanization and climate warming synergistically exacerbate habitat fragmentation and urban heat islands. However, existing studies often address the cold island effect and habitat quality in isolation and emphasize global mechanisms over site-specific spatial optimization. To construct a composite cold island–habitat quality network and to identify key thresholds in the network for collaboratively enhancing cooling effects and ecological quality, this study integrates morphological spatial pattern analysis, landscape connectivity, structural equation modeling, minimum cumulative resistance, and light gradient boosting machine (LightGBM) with Shapley additive explanations (SHAP) to identify critical patches, corridors, and barriers and to disentangle their drivers and thresholds. Results revealed that land surface temperature and habitat quality showed strong spatial clustering (Moran’s I : 0.930 and 0.765). The composite network comprises 50 multifunctional patches, 115 composite corridors, and 268 barriers. Structural equation modeling confirmed cascading driver effects. LightGBM and SHAP analysis identified water body connectivity (percentage of like adjacencies [PLADJ]), dominance (largest patch index [LPI]), edge density (ED), and patch density (PD) as pivotal drivers. To achieve simultaneous benefits, strategies must adhere to strict “common thresholds” defined by the stricter transition zones of the 2 objectives. Specifically, robust synergy requires landscape metrics to surpass critical intervals: PLADJ of water body (WB) must rise above ~96.1% to 96.4%, ED_WB should exceed ~61.0 to 75.0 m/hm 2 , and LPI_WB must maintain ≥55.3%. Furthermore, effective co-benefits emerge only when PD_WB approaches ~6.3 patches/100 hm 2 and when water body and forest coverage surpass the transition bands of ~30.9% to 47.0% and ~21.0% to 27.4%, respectively. These quantified targets translate complex response patterns into actionable guidance for restoring hydrological connectivity, naturalizing shorelines, and strengthening blue–green infrastructure in high-density megacities.