Abstract
Along with global climate change and the worldwide heat island phenomenon, developing climatic methods and planning practices for the benefit of thermal comfort is of increasing interest. Studies have focused on urban streets, studying the aspect ratio, the orientation, street vegetation patterns, etc. and how they affect thermal comfort. While the role of vegetation is undeniable, this paper asks the question whether the effects of a tree configuration does not vary under different street configurations, and if yes, how to select tree species and determine their appropriate layout. Here, an analytical framework is proposed to test the different tree configurations (changing one variable at a time) with the least favorable street configuration. It is confirmed that the east–west oriented streets are the least favorable cases and denser tree canopies are better for cooling. The interval between the trees are observed to have an optimal effect when it is equal to the crown width at maturity. Furthermore, the results show that the heat mitigation rate of a tree configuration is not linearly improved by the Aspect Ratio (AR). In the case of Shantou city, the improvement of thermal comfort slows down when the AR reaches 1.5 while Mangifera indica planted with 10 m intervals is recommended among the common street-tree species. Other species could be used also, but should meet the requirements of the canopy density and the interval of layout. The paper does not consider other configuration options such as asymmetrical cases of street geometry and one-side or axial tree planting, etc., but the framework allows for adding such options and simulating thermal comfort for a greater number of scenarios.
Highlights
Worldwide rapid urbanization and the corresponding shift from the natural environment to a densely built-up environment has raised many issues, among which city-induced climate change, especially the urban heat island phenomenon has stimulated much research interest [1]
Street tree configuration—defined by the tree type and the tree layout—is studied in terms of the effects they have on heat mitigation at pedestrian level (1.5 m–1.75 m) when combined with various street configuration—defined by the orientation and the aspect ratio
In order to detect which tree type and layout is optimal for heat mitigation in extreme summer conditions, even in the worst street configuration case, an analytical framework is proposed, composed of two main parts: a Spatial–Temporal Comfort Diagnosis—intended to identify the street configurations the least favorable for thermal comfort—and a Street Thermal Comfort Optimization—where different tree configurations are tested with the least favorable street configurations to evaluate their contributions to heat mitigation
Summary
Worldwide rapid urbanization and the corresponding shift from the natural environment to a densely built-up environment has raised many issues, among which city-induced climate change, especially the urban heat island phenomenon has stimulated much research interest [1]. Focusing on the climatic condition at the street level, it has been well-established that a street orientation and its Aspect Ratio (AR) both influence the pedestrian comfort [4,5,6]. Some authors refer to the combination of these two parameters (orientation and aspect ratio) as the street configuration [7]. The effects of street configurations on human thermal comfort have been studied by various scholars [6,8,9,10] resulting mostly in recommendations to consider through the design process. Thermal comfort optimization is often mentioned by various authors [12,13] as to signify the specific measures taken under difficult thermal conditions to improve that condition of mind and get it as close as possible to total satisfaction for the average user
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