Combined effects of climate and urban morphology on global urban heat

Urban structures are essential for human habitation, yet they profoundly alter surface energy balances, with significant environmental and health implications. Although urban heat island phenomenon is well recognized, the thermal influence of surrounding urban structures and its interaction with climate remain insufficiently understood. This study presents a global analytical framework that quantifies the thermal impact of surrounding structures, analyzes the combined effects of climate and urban morphology, and projects future thermal trajectories across 967 cities worldwide. By integrating climate variables and local climate zones with machine learning, we assess the thermal impacts of surrounding urban structures. Through a comprehensive weighting of the constituent thermal influences, we introduce the city-scale thermal impact of surrounding urban structures (TBE), revealing that climate and morphology jointly contribute to global urban heat. Across climate zones, cities exhibiting high daytime TBE are characterized by low- and mid-rise built form, whereas sparsely built types prevail in cities with low TBE. These patterns persist at night. Future projections show that the spatial patterns of TBE will be distinct from current conditions, with combined climate-structure effects will dominate urban thermal environment in almost half of global cities. These projections also reveal significant regional disparities between the Global South and the Global North. Our findings highlight the role of combined effects in shaping present and future urban heat, informing the need for adaptation strategies tailored to individual cities.