Multi-country multi-city study on heterogeneous impacts of urbanicity on heat-related mortality

Urbanicity might have complicated impacts on heat-related mortality, intertwined with national and regional context; however, the relevant evidence is limited. This multi-country study investigated the complex roles of urbanicity on heat-related mortality, considering spatial heterogeneity across different urban contexts. Through the Multi-City multi-Country (MCC) research collaborative network, the data on mortality and ambient temperature from 397 cities in 12 countries were collected, and we examined the heterogeneous associations between urbanicity characteristics and heat-mortality risk by region. Higher population density was associated with increased heat-mortality risk in North America and Europe, while the inverse association was observed in Latin America; however, the association was not significant in East Asia. Among urban environment factors, increased PM _2.5 concentrations, CO ₂ emissions, and urban heat island intensity generally contributed to a higher heat-mortality risk. Whereas greater greenness mitigated the heat-mortality risk, particularly in Europe. Our findings highlight heterogeneous roles of urbanicity on vulnerability to heat risk and could provide scientific evidence for establishing targeted urban health strategies against climate change.