Spatial configuration and time of day impact the magnitude of urban tree canopy cooling
Spatial configuration and time of day impact the magnitude of urban tree canopy cooling
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DOI：
10.1088/1748-9326/ac12f2
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发表时间：
2021
影响因子：
6.7
通讯作者：
M. Alonzo;M. Baker;Yuemeng Gao;V. Shandas
中科院分区：
文献类型：
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作者：
M. Alonzo;M. Baker;Yuemeng Gao;V. Shandas
树木覆盖通常与城市环境中较冷的空气温度有关，但冠层配置，空间背景和时间的作用还没有很好地理解。缺乏适当的空气温度数据，也许，过度依赖于一个单一的“树冠”类，模糊了树冠冷却的机制，阻碍了检查树木和城市气候之间的时空关系的能力。在这里，我们使用了在炎热的夏天的黎明前（pd），下午（aft）和晚上（eve）活动中在整个华盛顿，DC，美国汽车收集的>70 000个空气温度测量值。我们将树冠细分为“软”（在未铺装的表面）和“硬”（在铺装的表面）树冠类，并进一步划分软树冠分布（窄边）和丛生的补丁（与内部核心的边缘）。在每一级细分，我们预测的空气温度异常，使用广义加性模型的每一天的时间。我们发现，所有的“树冠”类在每个时间都线性冷却（pd = 0.5 °C ± 0.3 °C，aft = 1.8 °C ± 0.6 °C，eve = 1.7 °C ± 0.4 °C），但在下午可以解释为分别在低和高冠层覆盖下主要的硬和软冠层冷却的聚集效应。软冠层在下午非线性地冷却，影响最小，直到40%的覆盖，但在晚上在所有覆盖部分强烈（和线性）（pd = 0.7 °C ± 1.1 °C，aft = 2.0 °C ± 0.7 °C，eve = 2.9 °C ± 0.6 °C）。补丁冷却在一天中的任何时候，尽管不均匀的分配在整个城市，而更多的分布式冠层冷却在黎明前和傍晚，由于增加阴影。这一发现对城市热岛缓解规划很重要，因为它更容易找到分布式树木的种植空间，而不是森林斑块。
Tree cover is generally associated with cooler air temperatures in urban environments but the roles of canopy configuration, spatial context, and time of day are not well understood. The ability to examine spatiotemporal relationships between trees and urban climate has been hindered by lack of appropriate air temperature data and, perhaps, by overreliance on a single ‘tree canopy’ class, obscuring the mechanisms by which canopy cools. Here, we use >70 000 air temperature measurements collected by car throughout Washington, DC, USA in predawn (pd), afternoon (aft), and evening (eve) campaigns on a hot summer day. We subdivided tree canopy into ‘soft’ (over unpaved surfaces) and ‘hard’ (over paved surfaces) canopy classes and further partitioned soft canopy into distributed (narrow edges) and clumped patches (edges with interior cores). At each level of subdivision, we predicted air temperature anomalies using generalized additive models for each time of day. We found that the all-inclusive ‘tree canopy’ class cooled linearly at every time (pd = 0.5 °C ± 0.3 °C, aft = 1.8 °C ± 0.6 °C, eve = 1.7 °C ± 0.4 °C), but could be explained in the afternoon by aggregate effects of predominant hard and soft canopy cooling at low and high canopy cover, respectively. Soft canopy cooled nonlinearly in the afternoon with minimal effect until ∼40% cover but strongly (and linearly) across all cover fractions in the evening (pd = 0.7 °C ± 1.1 °C, aft = 2.0 °C ± 0.7 °C, eve = 2.9 °C ± 0.6 °C). Patches cooled at all times of day despite uneven allocation throughout the city, whereas more distributed canopy cooled in predawn and evening due to increased shading. This later finding is important for urban heat island mitigation planning since it is easier to find planting spaces for distributed trees rather than forest patches.