Increasing heat in urban environments has recently become one of the most dangerous climate hazards due to its adverse impacts on urban populations. Implementing street-level trees could be an effective strategy to mitigate pedestrian heat exposure, particularly due to their ability to block incoming solar radiation. In this study, the PALM model system was applied to simulate the effects of a tree canopy and its location on heat exposure, as quantified by the Universal Thermal Climate Index (UTCI), during a heat wave, using the example of Prague-Dejvice, Czech Republic. Our results show that trees reduce the UTCI under their canopy by 3.5 °C on average, with the greatest UTCI reduction in open spaces during mornings and afternoons. High spatio-temporal variations in the reduction of UTCI by a tree canopy were observed in the study domain, especially in street canyons and courtyards. The effectiveness of trees in mitigating heat exposure was found to be closely related to their individual location with respect to surrounding buildings, specifically: (i) the distance from the nearest building, (ii) the height of the nearest building, and (iii) the azimuthal angle of the vector from the nearest building towards the tree. Model simulations indicate that a particularly small reduction in UTCI (about 2.5 °C less than the mean) can be found under trees located in the shade of taller buildings that are within a few metres and between southwest and southeast of the trees. Our findings illustrate that tree positioning in cities should be undertaken carefully and thoughtfully so that the presence of trees effectively improves thermal comfort and urban quality of life.

中文翻译：

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迈向对气候负责的树木定位：树木对复杂城市环境中热暴露的详细影响


由于对城市人口的不利影响，城市环境中热量的增加最近已成为最危险的气候危害之一。种植街道树木可能是减轻行人热量暴露的有效策略，特别是因为它们能够阻挡入射的太阳辐射。在这项研究中，以捷克共和国布拉格-德伊维采为例，应用 PALM 模型系统来模拟树冠及其位置对热暴露的影响，如通用热气候指数 （UTCI） 所量化的那样。我们的结果表明，树木在其树冠下的 UTCI 平均降低了 3.5 °C，其中上午和下午开放空间的 UTCI 降低幅度最大。在研究领域观察到树冠降低 UTCI 的时空变化很大，尤其是在街道峡谷和庭院中。发现树木在减轻热量暴露方面的有效性与它们相对于周围建筑物的个体位置密切相关，特别是：（i） 与最近建筑物的距离，（ii） 最近建筑物的高度，以及 （iii） 从最近的建筑物到树木的矢量的方位角。模型模拟表明，在位于几米内、树木西南和东南之间的较高建筑物的树荫下，可以发现 UTCI 的降低特别小（比平均值低约 2.5 °C）。我们的研究结果表明，在城市中，树木的定位应该仔细和深思熟虑，以便树木的存在有效地提高热舒适度和城市生活质量。