[audio:http://wamcradio.org/EarthWise/wp-content/uploads/2012/02/EW-03-08-12-Cooling-Trees.mp3|titles=EW 03-08-12 Cooling Trees]
During the summer, it’s no surprise that suburban areas with trees seem cooler than urban pavement. Many cities, including New York City, are promoting tree-planting programs to benefit from the natural cooling that trees provide.
We all know that shade can shield us from the sun’s rays. But the cooling effect of trees extends beyond the umbrella effect of their canopies.
Trees take up water from the soil and evaporate it to the atmosphere. More accurately, this process is known as transpiration. Each gram of water that is evaporated carries away about 540 calories of heat, which has a cooling effect.
By transforming liquid water to vapor, trees remove heat from the environment. In a North Carolina study, converting a lawn to a pine forest cooled the temperature by nearly 3 degrees Celsius.
The way that vegetation is managed influences how much cooling we realize. A mature tree can remove 1 to 60 gallons of water from the soil each day. During the summer, conifers generally take up less water than deciduous trees. Among the latter, sycamores lose a lot more water than maples.
Next time you hear about your tax dollars being spent on tree plantings, think of the work that nature does for you in return. Trees add property value. And in their absence, our air conditioning bills would be much higher.
Photo, taken on April 26, 2007, courtesy of Ward Broughton via Flickr.