Spatial assessment of heat vulnerability and socio-environmental inequities in Tokyo

Urban populations are increasingly exposed to extreme heat, with vulnerability shaped by interacting environmental, demographic, and socioeconomic factors. This study assesses heat vulnerability across Tokyo’s 23 wards by constructing an integrated Heat Vulnerability Index (HVI) comprising three dimensions: Exposure (land surface temperature and tree canopy cover), Sensitivity (proportion of elderly residents and densely built wooden housing area), and Adaptive Capacity (household income). Spatial analysis reveals pronounced disparities, with high vulnerability concentrated in the northern and eastern wards, where elevated land surface temperatures, limited tree canopy, higher elderly populations, and lower income levels converge. The HVI demonstrates strong predictive validity, showing a highly significant correlation with ward-level heatstroke-related emergency transports. Among all indicators, the proportion of elderly residents and household income exhibit the strongest associations with heatstroke incidence. These findings highlight the need for equity-centered adaptation strategies that combine short-term financial and housing-level interventions with long-term environmental improvements such as urban greening. By linking environmental and social determinants of heat vulnerability, this study provides actionable evidence to mitigate heat-related health impacts in a super-aged, densely populated megacity.