The expansion of an urban tree canopy is a commonly proposed nature-based solution to combat excess urban heat. The influence trees have on urban climates via shading is driven by the morphological characteristics of trees, whereas tree transpiration is predominantly a physiological process dependent on environmental conditions and the built environment. The heterogeneous nature of urban landscapes, unique tree species assemblages, and land management decisions make it difficult to predict the magnitude and direction of cooling by transpiration. In the present article, we synthesize the emerging literature on the mechanistic controls on urban tree transpiration. We present a case study that illustrates the relationship between transpiration (using sap flow data) and urban temperatures. We examine the potential feedbacks among urban canopy, the built environment, and climate with a focus on extreme heat events. Finally, we present modeled data demonstrating the influence of transpiration on temperatures with shifts in canopy extent and irrigation during a heat wave.

中文翻译：

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树木蒸腾作用和城市温度：当前的理解、意义和未来的研究方向

城市树冠的扩展是一种普遍提出的基于自然的解决方案，以对抗城市过热。树木通过遮荫对城市气候的影响是由树木的形态特征驱动的，而树木蒸腾作用主要是依赖于环境条件和建筑环境的生理过程。城市景观的异质性、独特的树种组合和土地管理决策使得很难预测蒸腾作用的降温幅度和方向。在本文中，我们综合了有关城市树木蒸腾作用机制控制的新兴文献。我们提出了一个案例研究，说明蒸腾作用（使用树液流数据）与城市温度之间的关系。我们研究了城市冠层之间的潜在反馈，建筑环境和气候，重点关注极端高温事件。最后，我们提供了模型数据，证明了在热浪期间，随着冠层范围和灌溉的变化，蒸腾作用对温度的影响。