Sponsor
This material is based upon work supported by the National Science Foundation under Grant No. 1951647.
Published In
Environmental Research Letters
Document Type
Article
Publication Date
8-2021
Subjects
Trees in cities, Urban climatology, Energy conservation, Land use -- Environmental aspects, Shade trees
Abstract
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.
Rights
Copyright (c) 2021 The Authors
This work is licensed under a Creative Commons Attribution 4.0 International License.
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DOI
10.1088/1748-9326/ac12f2
Persistent Identifier
https://archives.pdx.edu/ds/psu/36385
Citation Details
Alonzo, M., Baker, M. E., Gao, Y., & Shandas, V. (2021). Spatial configuration and time of day impact the magnitude of urban tree canopy cooling. Environmental Research Letters, 16(8), 084028.