1] Yale-NUIST Center on Atmospheric Environment, Nanjing University of Information Science and Technology, Nanjing 210044, China [2] School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511, USA.
Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06511, USA.
Nature. 2014 Jul 10;511(7508):216-9. doi: 10.1038/nature13462.
The urban heat island (UHI), a common phenomenon in which surface temperatures are higher in urban areas than in surrounding rural areas, represents one of the most significant human-induced changes to Earth's surface climate. Even though they are localized hotspots in the landscape, UHIs have a profound impact on the lives of urban residents, who comprise more than half of the world's population. A barrier to UHI mitigation is the lack of quantitative attribution of the various contributions to UHI intensity (expressed as the temperature difference between urban and rural areas, ΔT). A common perception is that reduction in evaporative cooling in urban land is the dominant driver of ΔT (ref. 5). Here we use a climate model to show that, for cities across North America, geographic variations in daytime ΔT are largely explained by variations in the efficiency with which urban and rural areas convect heat to the lower atmosphere. If urban areas are aerodynamically smoother than surrounding rural areas, urban heat dissipation is relatively less efficient and urban warming occurs (and vice versa). This convection effect depends on the local background climate, increasing daytime ΔT by 3.0 ± 0.3 kelvin (mean and standard error) in humid climates but decreasing ΔT by 1.5 ± 0.2 kelvin in dry climates. In the humid eastern United States, there is evidence of higher ΔT in drier years. These relationships imply that UHIs will exacerbate heatwave stress on human health in wet climates where high temperature effects are already compounded by high air humidity and in drier years when positive temperature anomalies may be reinforced by a precipitation-temperature feedback. Our results support albedo management as a viable means of reducing ΔT on large scales.
城市热岛（UHI）是一种常见的现象，即城市地区的表面温度高于周围农村地区，这是地球表面气候受到的最显著的人为变化之一。尽管它们是景观中的局部热点，但 UHI 对城市居民的生活产生了深远的影响，城市居民占世界人口的一半以上。阻碍 UHI 缓解的一个障碍是缺乏对 UHI 强度各种贡献的定量归因（表示为城市和农村地区之间的温差，ΔT）。人们普遍认为，城市土地蒸发冷却的减少是导致ΔT 的主要驱动因素（参考文献 5）。在这里，我们使用气候模型表明，对于北美的城市，白天ΔT 的地理差异主要是由城市和农村地区向低层大气输送热量的效率变化来解释的。如果城市地区的空气动力学比周围的农村地区更平滑，那么城市的热量散发效率就相对较低，城市就会变暖（反之亦然）。这种对流效应取决于当地的背景气候，在潮湿气候中增加白天ΔT3.0±0.3 开尔文（平均值和标准误差），但在干燥气候中减少ΔT1.5±0.2 开尔文。在美国潮湿的东部地区，有证据表明在较干燥的年份ΔT 更高。这些关系意味着，在高湿度已经使高温效应复杂化的潮湿气候中，以及在正温度异常可能因降水-温度反馈而得到加强的干燥年份中，UHI 将加剧热浪对人类健康的压力。我们的研究结果支持反照率管理作为一种可行的方法，可以在较大范围内降低ΔT。
