Urban heat mitigation is a pressing concern for cities. Intense urban heat poses a threat to human health and urban sustainability. Tree planting is one of the most widely employed nature-based heat mitigation methods worldwide. Therefore, city policy makers require knowledge of how much temperature will be reduced by increasing urban tree canopy (UTC). Cooling efficiency (CE), which was been proposed to quantify the magnitude of temperature reduction associated with a 1% increase in UTC, has been primarily investigated at smaller scales previously. However, such small-scale results cannot be used to develop policy at the whole-city scale. This study developed a method that reveals the scaling relations of CE so as to predict its effects at the city scale. CE was found to follow the form of a power law as spatial scale increased from the small analytical units through intermediate size units up to the extent of a whole city. The power law form appeared consistently across cities with different climate backgrounds during summer daylight hours. Furthermore, the power law form was robust within cities under different summer weather conditions. The power-law scaling approach can thus be used to predict CE at the whole-city scale, providing a useful tool for managers to set UTC goals to mitigate extreme urban heat.

中文翻译：

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预测城市树木冠层降温效率的缩放定律


城市供热缓解是城市面临的一个紧迫问题。城市酷热对人类健康和城市可持续性构成威胁。植树是全球应用最广泛的基于自然的热缓解方法之一。因此，城市政策制定者需要了解增加城市树冠 （UTC） 将降低多少温度。冷却效率 （CE） 被提议用于量化与 UTC 增加 1% 相关的温度降低幅度，以前主要在较小尺度上进行研究。然而，这种小规模的结果不能用于在整个城市范围内制定政策。本研究开发了一种方法，可以揭示 CE 的缩放关系，从而预测其在城市尺度上的影响。发现 CE 遵循幂律的形式，因为空间尺度从小型分析单元增加到中等大小的单元，直到整个城市的范围。幂律形式在夏季白天在不同气候背景的城市中一致出现。此外，在不同夏季天气条件下，城市内的幂律形式是稳健的。因此，幂律缩放方法可用于预测整个城市尺度的 CE，为管理人员设定 UTC 目标以缓解极端城市高温提供了有用的工具。