Cooling-resource mismatch and residual heat exposure among vulnerable populations in high-density Singapore: an equity-oriented diagnostic framework

Urban heat adaptation in high-density tropical cities requires understanding not only where thermal exposure is concentrated, but also whether available cooling resources adequately support vulnerable populations. However, existing assessments often examine thermal exposure and cooling resources separately, with limited integration of residual heat conditions and population vulnerability. This study develops a diagnostic framework integrating land surface temperature, vegetation, water resources, covered walkway infrastructure, and age-specific population data to characterize surface heat pressure (SHP), cooling-resource support (CRSI), residual heat exposure (RHE), vulnerable heat exposure (VHE), and equity-related risk (ERI) using a 100 m spatial framework in Singapore. We found that high surface heat pressure did not necessarily translate into high residual heat exposure, as cooling-resource support modified the spatial patterns of residual heat risk. VHE and ERI, representing exposure scale and distributional disadvantage respectively, did not fully overlap, indicating distinct intervention needs. Priority zones were identified where elevated residual heat exposure, limited cooling support, and concentrations of age-related vulnerable groups coincided, revealing deficits in natural cooling resources and sheltered pedestrian infrastructure. The framework provides a spatial basis for targeted heat adaptation by integrating thermal pressure, cooling-support capacity, and equity-related vulnerability in compact tropical cities.