Accurately capturing the impact of urban trees on temperature can help optimize urban heat mitigation strategies. Recently, there has been widespread use of remotely sensed land surface temperature (T _s) to quantify the cooling efficiency (CE) of urban trees. However, remotely sensed T _s reflects emitted radiation from the surface of an object seen from the point of view of the thermal sensor, which is not a good proxy for the air temperature (T _a) perceived by humans. The extent to which the CEs derived from T _s reflect the true experiences of urban residents is debatable. Therefore, this study systematically compared the T _s-based CE (CE _{T s}) with the T _a-based CE (CE _{T a}) in 392 European urban clusters. CE _{T s} and CE _{T a} were defined as the reductions in T _s and T _a, respectively, for every 1% increase in fractional tree cover (FTC). The results show that the increase in FTC has a substantial impact on reducing T _s and T _a in most cities during daytime. However, at night, the response of T _s and T _a to increased FTC appears to be much weaker and ambiguous. On average, for European cities, daytime CE _{T s} reaches 0.075 °C %⁻¹, which is significantly higher (by an order of magnitude) than the corresponding CE _{T a} of 0.006 °C %⁻¹. In contrast, the average nighttime CE _{T s} and CE _{T a} for European cities are similar, both approximating zero. Overall, urban trees can lower daytime temperatures, but the magnitude of their cooling effect is notably amplified when using remotely sensed T _s estimates compared to in situ T _a measurements, which is important to consider for accurately constraining public health benefits. Our findings provide critical insights into the realistic efficiencies of alleviating urban heat through tree planting.

中文翻译：

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地表温度带来的城市树木白天降温效率远高于气温带来的降温效率

准确捕捉城市树木对温度的影响有助于优化城市散热策略。近年来，遥感地表温度得到广泛应用（时间 _s ) 量化城市树木的冷却效率 (CE)。然而，遥感时间 _s反射从热传感器的角度看到的物体表面发射的辐射，这不能很好地代表空气温度（时间 _a ) 被人类感知。 CE 的衍生程度时间 _其是否反映城市居民的真实经历值得商榷。因此，本研究系统地比较了时间 _基于s的 CE (CE _{时间 s} ) 与时间 _基于a的CE（CE _{时间 a} ) 392 个欧洲城市群。 CE _{时间 和}CE _{时间 a}被定义为减少时间 _沙​时间 _a，分别表示树木覆盖率 (FTC) 每增加 1%。结果表明，FTC的增加对减少时间 _沙​时间 _a大多数城市白天。然而，到了晚上，回应时间 _沙​时间 _{增加 FTC 的要求}似乎要弱得多且含糊不清。平均而言，对于欧洲城市来说，白天的 CE _{时间 s}达到 0.075 °C % ⁻¹，明显高于相应的 CE（一个数量级） _时间 0.006℃% ^-1的_a。相比之下，平均夜间CE _{时间 和}CE _{时间 欧洲城市的a}相似，均接近于零。总体而言，城市树木可以降低白天温度，但使用遥感技术时，其降温效果的程度会显着放大时间 _s估计值与原位T _a衡量标准，对于准确限制公共卫生效益而言，考虑这一点非常重要。我们的研究结果为通过植树缓解城市热量的实际效率提供了重要的见解。