Abstract The physical nature of the built urban environment gives rise to urban heat islands (UHI), making many cities frequently thermally uncomfortable in the summer, with potentially serious effects on human health. When climate change effects of higher summer temperatures and prolonged heatwaves are factored in, it is clear that adaptive measures are needed to ensure the liveability of cities. The shade provided by planting trees is one such adaptation measure. This study, in Bolzano, Italy, used a thermal camera to record the surface temperatures of three common urban surfaces – asphalt, porphyry, and grass – in the shade of 332 single tree crowns, of 85 different species, during the peak temperature period of summer days. By comparing with the temperature of adjacent unshaded ground, estimates of the degree of surface cooling were made. Measurements at three locations within the shadow revealed higher cooling in the centre and at the western edge. The cooling was related to a multitude of tree traits, of which Leaf Area Index estimate (LAIcept) and crown width were the most important. Median average cooling of 16.4, 12.9 and 8.5 °C was seen in the western edge of the tree shade for asphalt, porphyry and grass, respectively. Maximum temperatures were reduced by roughly 19 °C for all surface types. Coniferous trees were capable of providing high cooling, however, crown dimensions may limit the receiving surface area. Descriptive and predictive multiple linear regression models were able to predict cooling with some success from several of the predictor variables (LAIcept and gap fraction). Strategic planting of single trees in cities can have significant impacts on the absorption of solar radiation by ground surface materials thus reducing the heat storage that contributes to UHIs.

中文翻译：

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树木性状对城市地表遮荫降温的影响

摘要 城市建成环境的物理性质导致了城市热岛（UHI）的产生，使许多城市在夏季经常出现热不舒服，对人类健康可能产生严重影响。考虑到夏季高温和长时间热浪对气候变化的影响，显然需要采取适应性措施来确保城市的宜居性。植树遮荫就是这样一种适应措施。这项在意大利博尔扎诺进行的研究使用热像仪记录了三种常见的城市表面——沥青、斑岩和草地——在 85 种不同树种的 332 个单树冠的树荫下，在最高温度期间的表面温度。夏季天。通过与相邻无阴影地面的温度进行比较，对地表冷却程度进行了估计。在阴影内的三个位置进行的测量显示，中心和西部边缘的冷却程度更高。降温与多种树木性状有关，其中叶面积指数估计值 (LAIcept) 和树冠宽度是最重要的。沥青、斑岩和草地的树荫西缘的平均冷却温度分别为 16.4、12.9 和 8.5 °C。所有表面类型的最高温度降低了大约 19 °C。针叶树能够提供高冷却，但是，树冠尺寸可能会限制接收表面积。描述性和预测性多元线性回归模型能够从几个预测变量（LAIcept 和间隙分数）中成功预测冷却。