Patch size of trees affects its cooling effectiveness: A perspective from shading and transpiration processes
Patch size of trees affects its cooling effectiveness: A perspective from shading and transpiration processes
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树木的斑块大小影响其冷却效果：从遮荫和蒸腾过程的角度来看
DOI：
10.1016/j.agrformet.2017.08.013
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发表时间：
2017-12-15
影响因子：
6.2
通讯作者：
Qian, Yuguo
中科院分区：
文献类型：
--
作者：
Jiao, Min;Zhou, Weiqi;Qian, Yuguo
越来越多的城市绿空间，尤其是树木，已被广泛认为是减轻城市热量的有效手段。然而，许多不确定性发生在树木的空间构型如何影响它们的冷却效果上。城市规划师的一个常见问题是，大型绿空间补丁是否比几个较小的补丁具有更好的冷却效果，反之亦然。在这里，我们试图通过研究树木大小对两个关键冷却过程的影响来解决这个问题：阴影和蒸腾。我们选择了两种典型的树种，Ginkgo biloba和Popubis tomentosa，具有4种不同的斑块大小，并在北京进行了研究。我们将空气温度，相对湿度和蒸腾速率的现场测量与模型模拟整合在一起，并在斑块和斑点内进行了分析。我们发现：（1）较小的斑块的温度较高，湿度较低，温度和湿度的内部变化较大。 （2）具有固定的树盖面积，许多小斑块比单个大斑块可以提供更多的阴影，这表明将较小贴片分为较小的斑块而单调增加了阴影。 （3）斑块大小和蒸腾率之间存在非线性关系，这表明在一定的斑块大小时可能会发生最大蒸腾率。通过考虑阴影和蒸腾的关节效应，可能会发生最佳的斑块大小，在该斑点和蒸腾的关节效应最大化。
Increasing urban greenspace, particularly trees, has been widely recognized as an effective means for urban heat mitigation. Lots of uncertainty, however, occurs on how spatial configuration of trees affects their cooling effectiveness. A frequently asked question from urban planners is that whether a large greenspace patch has better cooling effects than several smaller ones, or vice versa. Here, we attempted to address this question by investigating the effects of patch size of trees on the two key cooling processes: shading and transpiration. We chose two typical tree species, Ginkgo biloba and Popubis tomentosa, with 4 different patch sizes, and conducted the research in Beijing. We integrated field measurements of air temperature, relative humidity and transpiration rate with model simulation, and conducted the analysis at both the patch and within-patch level. We found: (1) Smaller patches had higher temperature, lower humidity and greater within-patch variations in temperature and humidity than larger ones. (2) With a fixed area of tree cover, a number of small patches can provide more shade than a single large patch, suggesting a monotonic increase of shade provision with the division of a large patch into smaller ones. (3) There was a non-linear relationship between patch size and transpiration rate, suggesting a maximum transpiration rate might occur at certain patch size. By considering the joint effects of shading and transpiration, an optimal size of patch might occur, at which the joint effects of shading and transpiration are maximized.