街谷行道树种植对环境热舒适度的影响及适应性设计研究进展

行道树种植通常被作为改善城市街谷近地微气候的重要策略,如何发挥行道树对街谷热舒适度的提升潜力受到诸多学者的广泛关注。近年来“行道树种植与街谷热舒适度”相关研究获得了丰硕成果,通过总结梳理可将其归纳为行道树树木个体形态对热舒适度的调控、行道树绿带空间配置与街谷热舒适度整体提升的关联性、适应不同街谷空间形态的行道树种植设计策略等三个研究主题。在深入分析既有研究成果基础上,提出了一套改善热舒适度的街谷行道树种植设计方案技术框架。最后,分别从建立响应地域气候特征的街谷行道树种植设计模式、构建街谷环境热舒适度模拟评估导则、制定街谷环境热舒适度评价标准等方面开展深入讨论,以期为后续城市街谷绿化提升热环境的研究提供思路和借鉴。

Review on the Influence of Tree Planting on the Outdoor Thermal Comfort and Its Adaptive Design in Street Canyons

Tree planting is an important strategy for improving the thermal environment of street canyons because of its positive effect on the microclimate. How to optimize tree planting to achieve the best effect in improving thermal comfort has attracted widespread attention. Clarifying the regulation mechanism of tree planting in street canyons is crucial to fully harnessing the positive impact of street trees on outdoor thermal comfort. In recent years, research on the regulation of tree planting on the thermal comfort of street canyons has been growing. Numerous studies have demonstrated that street tree planting involves a complex mechanism for regulating the thermal environment in street canyons. The enhancement or reduction of thermal comfort depends on the interaction between various factors, including the individual morphological characteristics of trees, the spatial configuration of green belts, and the geometry of street canyons. Therefore, it is necessary to evaluate the synergistic effects of the spatial morphology of street canyons and the tree planting approach on thermal comfort, to formulate a design strategy for tree planting compatible with the specific street canyon environment, aiming to maximize the ecological benefits of street trees.Most studies have investigated the influence of tree planting on outdoor thermal comfort in street canyons. In this paper, it reviewed the current research on thermal comfort regulation by street tree planting in canyons, summarised the impact factors of street trees on thermal comfort regulation in canyons, analyzed the limitations of the current research as well as the key issues that need to be focused on, and explored the tendency of the future research, to provide relevant references and inspirations for the follow-up work. The relevant research from 2000 to 2022 can be divided into three themes: 1) the impact of individual morphology of trees on outdoor thermal comfort in typical street canyons, which mainly discusses the effects of morphological characteristics such as leaf area, crown diameter, crown shape, and trunk height on the thermal comfort of street canyons, so as to provide a basis for the selection of street tree species; 2) the influence of spatial configuration of tree green belts on outdoor thermal comfort in typical street canyons, which focuses on exploring the influence of street tree green belt space configuration parameters on outdoor thermal comfort, such as planting spacing, arrangement, green coverage, the purpose of which is to guide the allocation mode of street trees; 3) planting strategies of street trees adapted to different spatial geometries of street canyons, which evaluates the improvement benefits of street tree greening design schemes in street canyons with different orientations and aspect ratios, and then refines the street tree planting design strategy to match the characteristics of the local environment. Previous studies have shown that considering a variety of individual morphological factors such as leaf area, crown diameter and trunk height of trees is the key to the scientific selection of tree species for street tree planting orientated towards thermal comfort improvement. The effect of thespatial configuration of trees on thermal comfort in street canyons varies greatly in different climatic zones, and the range of optimal green coverage in the corresponding climatic zones needs to be further determined. Due to the difference in latitude of each region, the angle of the sun will be different, and it is necessary to comprehensively consider the direction of the street canyon and the orientation of solar radiation in the corresponding region to determine the optimal location of street trees. Based on summarizing the influence factors of street trees on outdoor thermal comfort, to leverage the ecological benefits of street tree greening to improve the thermal environment of canyons, it proposes the design strategy of tree planting in the street canyon with different aspect ratios and formulate a street tree planting design scheme generation and optimization method framework for the thermal comfort enhancement of the canyon environment.Finally, combining the limitations of current research and the key issues that need to be addressed, several aspects worthy of further discussion are suggested, including the establishment of the street tree planting design model in response to local climate characteristics, the formulation of guidelines for simulation and evaluation of outdoor thermal comfort in street canyons, and the development of evaluation criteria for outdoor thermal comfort in street canyons. The study provides ideas and lessons for subsequent research on greening urban street canyons to enhance the thermal environment.