Institute of Environmental Engineering, ETH Zurich, Zurich, Switzerland.
Department of Civil, Environmental and Geomatic Engineering, University College London, London, UK.
Nature. 2019 Sep;573(7772):55-60. doi: 10.1038/s41586-019-1512-9. Epub 2019 Sep 4.
Urban heat islands (UHIs) exacerbate the risk of heat-related mortality associated with global climate change. The intensity of UHIs varies with population size and mean annual precipitation, but a unifying explanation for this variation is lacking, and there are no geographically targeted guidelines for heat mitigation. Here we analyse summertime differences between urban and rural surface temperatures (ΔT) worldwide and find a nonlinear increase in ΔT with precipitation that is controlled by water or energy limitations on evapotranspiration and that modulates the scaling of ΔT with city size. We introduce a coarse-grained model that links population, background climate, and UHI intensity, and show that urban-rural differences in evapotranspiration and convection efficiency are the main determinants of warming. The direct implication of these nonlinearities is that mitigation strategies aimed at increasing green cover and albedo are more efficient in dry regions, whereas the challenge of cooling tropical cities will require innovative solutions.
城市热岛（UHI）加剧了与全球气候变化相关的热相关死亡率的风险。UHI 的强度随人口规模和年平均降水量而变化，但这种变化缺乏统一的解释，也没有针对热缓解的地理目标指南。在这里，我们分析了全球夏季城市和农村地表温度之间的差异（ΔT），发现ΔT 与降水呈非线性增加，这受水分或能量对蒸散的限制控制，并调节了ΔT 与城市规模的比例关系。我们引入了一个粗粒度的模型，将人口、背景气候和 UHI 强度联系起来，并表明蒸散和对流效率的城乡差异是变暖的主要决定因素。这些非线性的直接含义是，旨在增加绿色覆盖和反照率的缓解策略在干燥地区更为有效，而冷却热带城市的挑战将需要创新的解决方案。
