Heat vulnerability caused by physical and social conditions in a mountainous megacity of Chongqing, China

• A heat vulnerability model is established coupled with physical and social conditions based on exposure, sensitivity and adaptation. • Spatial distribution of heat vulnerability is consistent with heat perception obtained from local social media. • High physical and low social heat vulnerabilities concentrate in central areas, while low physical and high social heat vulnerabilities concentrate in suburban areas. • Mitigation and adaptation strategies are proposed based on the heat vulnerability for urban planners and managers. Long-lasting heatwaves have seriously threatened human health. Exploring the distribution of heat vulnerability is important for urban risk management. A model of heat vulnerability coupled with physical and social conditions based on exposure, sensitivity, and adaptation was established in Chongqing, a mountainous megacity in China, and 11 indicators were adopted to assess heat vulnerability. Heat perception evaluated by social media data is used to validate heat vulnerability. Four primary outcomes emerged. First, integration of high physical and low social heat vulnerabilities was found in central areas, while low physical and high social heat vulnerabilities were concentrated in suburban areas. Second, the spatial distribution of heat vulnerability is consistent with that of heat perception. Third, high social exposure, high physical and social sensitivity, and low physical adaptation led to high heat vulnerability in central areas, while high heat vulnerability in suburban areas was primarily caused by high physical exposure and low social adaptation. Finally, due to the barriers of mountains and rivers, both physical and social heat vulnerabilities form unique decentralized patterns following urbanization. According to the finding of heat vulnerability, mitigative and adaptive strategies (e.g. hierarchical layouts, green measures, and vulnerable health databases) are proposed to improve climate resilience.