The shade of a single tree is a welcome source of relief on a hot summer day. But even a relatively small patch of woods can have a profound cooling effect. A new study at the University of Wisconsin-Madison looks at the role trees play in keeping towns and cities cool.
According to the study, the right amount of tree cover can lower daytime temperatures in the summer by as much as 10 degrees. The effects are noticeable from neighborhood to neighborhood and even on a block-by-block basis.
Cities are well-known to be hot spots due to the urban heat islanding effect. Using trees to keep temperatures more comfortable in cities can make a big difference for the people who live and work there.
The man-made structures of cities – roads, sidewalks, and buildings – absorb heat from the sun during the day and slowly release it at night. Trees, on the other hand, not only shade those structures from the sun, but they also transpire -or release water in the air through their leaves – which helps to cool things down.
According to the study, to get maximum cooling benefits, tree canopies must exceed forty percent, meaning that city blocks need to be nearly halfway covered by tree branches and leaves. To get the biggest bang for the buck, cities should start planting more trees in areas that are already near the forty percent threshold. But
trees can’t just be in parks. They need to be in places where people are active.
If we want the places where we live to be more comfortable and resilient in a warming world, we need to plant more trees.
Photo, posted May 26, 2012, courtesy of Mislav Marohnic via Flickr.