Dual impact of global urban overheating on mortality

It is known that the urban heat island (UHI) effect could increase mortality in hot seasons, yet its potential health benefits during cold spells are often overlooked. Here we assess the beneficial and detrimental impacts of the UHI effect and associated cooling strategies on temperature-related mortality in more than 3,000 cities worldwide by integrating multi-source datasets. This study finds that the UHI effect reduces global cold-related mortality, surpassing the increase in heat-related mortality more than fourfold. Widely implemented urban cooling strategies, including green and reflective infrastructure, can have an adverse net effect in high-latitude cities but benefit a few tropical cities. We propose seasonal adjustments to roof albedo as an actionable strategy to reduce heat- and cold-related mortality. Our findings highlight that urban heat can protect against mortality in most non-tropical cities in the cold season, emphasizing the importance of seasonally and place-based adaptive UHI mitigation strategies to reduce temperature-related mortality.