Abstract
Trees in urban areas have significant effects on the urban ecosystem. They can be used to improve the water cycle in urban areas by increasing evaporation and reducing runoff through rainfall interception. Street trees placed in planters on impervious areas reduce runoff by intercepting rainfall and by temporarily storing raindrops on leaves. Therefore, understanding tree canopy geometry and the effect of rainfall interception is important in urban hydrology. In this study, we assessed the effect of tree canopy morphology on rainfall interception using four major street tree species, Sophora japonica L., Ginkgo biloba L., Zelkova serrata (Thunb.) Makino, and Aesculus turbinata Blume, in Seoul, South Korea. We measured throughfall for each tree and also derived three-dimensional data of tree canopy morphology with a terrestrial laser scanner. Tree height, canopy crown width, leaf area index (LAI), leaf area density, mean leaf area, and mean leaf angle were used to determine canopy morphology. The interception rate was mostly affected by the LAI; a higher LAI tended to result in a higher interception rate. Leaf area affected the rainfall interception rate when trees had similar LAIs. These findings on individual tree canopy rainfall interception can help us to understand the importance of rainfall interception in hydrology and for ecological restoration when planning urban green spaces.
Highlights
In the urban environment, trees play critical roles by balancing the water cycle and modifying local climate conditions (Guevara-Escobar et al 2007; Natuhara 2018)
As it is not always feasible to expand the amount of green space in dense urban areas with a high proportion of impervious surface area to increase surface water infiltration and reduce runoff, it is important to select tree species with high rainfall interception to help improve the urban water cycle
Other canopy properties affect interception, such as mean leaf area and leaf area density (LAD), which affect the capacity of a tree to store rainfall (Baptista et al 2018; Holder 2013; Holder and Gibbes 2017)
Summary
Trees play critical roles by balancing the water cycle and modifying local climate conditions (Guevara-Escobar et al 2007; Natuhara 2018). Trees are important in urban catchment hydrology because of the interception of rainfall by their canopies. Interception of rainfall by the canopy reduces beneath-canopy throughfall and reduces runoff in urban catchments. In an urban environment with a high percentage of impervious surfaces, increasing interception and evaporation of rainfall and reducing runoff are crucial to restoring the urban water cycle to its natural condition (Livesley et al 2014). As it is not always feasible to expand the amount of green space in dense urban areas with a high proportion of impervious surface area to increase surface water infiltration and reduce runoff, it is important to select tree species with high rainfall interception to help improve the urban water cycle. Some drops directly pass through foliage and gaps between branches to reach the ground, which is called “free throughfall.” The raindrops intercepted by leaves or branches are temporarily stored on their surfaces (Xiao and McPherson 2016) and eventually evaporate after the rainfall has stopped
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