Most global heat assessments rely on exposure-only indicators. However, heat risk in cities extends beyond climatic extremes and is mediated by social vulnerabilities and infrastructural capacities that determine how populations experience and respond to heat. Here, we map heat risk globally in cities with populations over one million using a harmonised composite index disaggregated into hazard exposure, vulnerability, and coping capacity. Hazard exposure is characterised using the population-weighted Universal Thermal Climate Index (UTCI)-based Cooling Degree Days, which capture cumulative heat stress. Vulnerability and coping capacity are characterised by economic capacity, demographic structure, and infrastructural factors. The results show that over 95% of the highest-risk cities are concentrated in South and Southeast Asia and Sub-Saharan Africa. They also demonstrate that exposure alone is insufficient to predict risk. Several highly exposed cities (e.g., Bangkok, Jeddah) rank lower due to strong coping capacity, while others (e.g., Karachi, Faisalabad, Kaduna) face severe risk under moderate exposure. Our component-resolved risk analysis also reveals within-region heterogeneity, highlighting the need for spatially resolved, socio-economically contextualised approaches to heat adaptation by reducing exposure, addressing socioeconomic vulnerability, and investing in infrastructure to advance urban heat resilience in a rapidly warming world.
Authors: Nethmi Jayaratne Kariyawasam, Jesus Lizana, Radhika Khosla.
