The urban heat island effect (UHI) has been widely observed globally, causing climate, health, and energy impacts in cities. The UHI intensities have been found to largely depend on background climate and the properties of the urban fabric. Yet, a complete mechanistic understanding of how UHIs develop at a global scale is still missing. Using an urban ecohydrological and land-surface model (urban Tethys-Chloris) in combination with multi-source remote sensing data, we performed simulations for 49 large urban clusters across the Northern Hemisphere in 2009–2019 and analysed how surface and canopy air UHIs (SUHI and CUHI, respectively) develop during day and night. Biophysical drivers triggering the development of SUHIs and CUHIs have similar dependencies on background climate, but with different magnitudes. In humid regions daytime UHIs can be largely explained by the urban-rural difference in evapotranspiration, whereas heat convection and conduction are important in arid areas. Plant irrigation can largely promote daytime urban evapotranspiration only in arid and semi-arid climates. During night, heat conduction from the urban fabric to the environment creates large UHIs mostly in warm arid regions. Overall, this study presents a mechanistic quantification of how UHIs develop worldwide and proposes viable solutions for sustainable climate-sensitive mitigation strategies.

城市热岛效应 (UHI) 已在全球范围内广泛观察到，对城市的气候、健康和能源造成影响。已发现 UHI 强度在很大程度上取决于背景气候和城市结构的特性。然而，对 UHIs 如何在全球范围内发展的完整机械理解仍然缺失。我们使用城市生态水文和地表模型（城市 Tethys-Chloris）结合多源遥感数据，对 2009-2019 年北半球的 49 个大型城市群进行了模拟，并分析了地表和冠层空气 UHIs（ SUHI 和 CUHI 分别）在白天和晚上发育。触发 SUHI 和 CUHI 发展的生物物理驱动因素对背景气候具有相似的依赖性，但幅度不同。在潮湿地区，白天的 UHI 很大程度上可以用蒸发量的城乡差异来解释，而在干旱地区，热对流和传导很重要。只有在干旱和半干旱气候条件下，植物灌溉才能在很大程度上促进白天的城市蒸散。在夜间，从城市结构到环境的热传导主要在温暖干旱地区产生大型 UHI。总体而言，本研究对 UHI 如何在全球范围内发展进行了机械量化，并为可持续的气候敏感型缓解战略提出了可行的解决方案。从城市结构到环境的热传导主要在温暖干旱地区产生大型 UHI。总体而言，本研究对 UHI 如何在全球范围内发展进行了机械量化，并为可持续的气候敏感型缓解战略提出了可行的解决方案。从城市结构到环境的热传导主要在温暖干旱地区产生大型 UHI。总体而言，本研究对 UHI 如何在全球范围内发展进行了机械量化，并为可持续的气候敏感型缓解战略提出了可行的解决方案。