Trees play a crucial role in keeping cities cool, which is increasingly important as we face climate change’s rising temperatures…
On a hot summer’s day, the shade of a single tree can provide welcome relief. However, when that tree is part of a small forest, it creates a profound cooling effect.
This according to a study published in the Proceedings of the National Academy of Sciences that found that the right amount of tree cover can lower summer daytime temperatures by as much as 10 degrees Fahrenheit (-12,2 degrees Celsius).
Preparing for heatwaves
With climate change making extreme heat events more common each summer, city planners are working on how to prepare.
Heatwaves drive up energy demands and costs and can have big human health impacts.
Trees could be the secret to keeping the places we live liveable.
How trees keep us cool
Monica Turner, a University of Wisconsin-Madison professor in the Department of Integrative Biology and a co-author of the study, says that impervious surfaces – like roads, sidewalks and buildings – absorb heat from the sun during the day and slowly release that heat at night.
Trees, on the other hand, not only shade those surfaces from the sun’s rays, but they also transpire or release water into the air through their leaves, a process that cools things down.
How many trees do we need to keep our cities cool?
To get the maximum benefit of this cooling service, the study found that tree canopy cover must exceed 40 percent.
In other words, an aerial picture of a single city block would need to be nearly half-way covered by a leafy green network of branches and leaves.
“Tree canopy cover can actually do more than offset the effects of impervious surfaces,” says Carly Ziter, lead author of the paper. During the day, “an equivalent amount of canopy cover can cool the air down more than pavement will warm it up
Plant trees with your neighbours
“It’s not really enough to just kind of go out and plant trees, we really need to think about how many we’re planting and where we’re planting them,” she says.
“We’re not saying planting one tree does nothing, but you’re going to have a bigger effect if you plant a tree and your neighbour plants a tree and their neighbour plants a tree.”
Ziter says that the trees we plant now or the areas we pave now are going to be determining the temperatures of our cities in the next century.
Source: University of Wisconsin-Madison via www.sciencedaily.com
With it being Arbour Week (1 – 7 September) now is the perfect time plan planting trees with your neighbours, friends and family.
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