First, because this relationship is linear, it suggests there is no threshold tree cover required to affect air temperature; instead, every bit of additional tree canopy seems to help reduce local air temperature on hot days. Thus, planting more trees in areas where there are none is likely to lead to cooling in those locations. To me, this offers hope that we can all make a difference by planting trees—even one tree!—and we can all experience positive impacts from urban trees at local scales.
Second, based on a recent urban heat island analysis in Tacoma, the GRIT neighborhood is 5-6ºF hotter than some neighborhoods in Tacoma. Our research is ongoing, and we are continuing to evaluate how tree cover within this neighborhood impacts temperature at a very local scale, most immediately within 10 meters or so (just over 30 feet). Meanwhile, we’re trying to understand how other factors at larger spatial scales, greater than 10 meters, also effect temperature, including hard surfaces such as roads, driveways, sidewalks or roofs and the percentage of tree cover present across an entire neighborhood or city.
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