Heat risk during hot weather is associated with poorer self-reported mental health: A cross-sectional study in Shanghai, China

Background: As global warming increases, hot weather is recognized as a mental health risk. Previous studies, however, mainly focused on the direct effects of heat hazards, overlooking heat exposure, sensitivity, and adaptation. Aim: To assess the role of heat exposure, sensitivity, and adaptation in the heat hazard–mental health association during hot weather. Methods: We conducted a cross-sectional survey of 1347 adults in Shanghai, China, in the summer of 2023 via the hazard-exposure-vulnerability framework. Mental health was self-reported based on the five-item Mental Health Inventory (MHI-5). We developed a moderated serial mediation model to examine the associations between heat risk and mental health, and heat hazard was represented as thermal comfort. Mediators included adaptive behaviors, a heat adaptation component, and outdoor activity duration, a proxy measure for heat exposure. Moderators included perceived sensitivity to heat hazards and adaptive conditions. Results: Increased heat hazards were associated with poorer mental health, with 88 % of the effect being direct, and 12 % mediated by adaptive behaviors that increased exposure risk and outdoor activity duration. The single mediating effect of adaptive behavior was associated with poorer mental health. The serial mediation of adaptive behavior and outdoor activity duration was associated with greater mental health. The moderators of perceived sensitivity to heat hazards and adaptive conditions were associated with poorer mental health. Conclusions: While direct heat hazards have the largest effect on mental health, our findings highlight the significant mediating and moderating roles of heat exposure, adaptive behaviors, and conditions, which should be considered.