Earth & Sky

Green roofs clean rainwater runoff

Atlanta, GA city hall greenroof (EPA)

DB: This is Earth & Sky on the growing popularity of what are called “green roofs.”

JB: Rain that falls in urban areas typically flows into sewers and storm drains. This urban runoff has been found to contribute greatly to pollution in rivers, lakes, the ocean, and other natural bodies of water. It’s been estimated that some cities need nearly a billion dollars each in upgrades to their storm water systems, in order to comply with the U.S. Clean Water Act.

DB: That’s why some communities are turning to alternatives such as “green roofs.” David J. Beattie is director of the Penn State Center for Green Roof Research. He told us that a green rooftop is designed to be covered with hardy plants that grow in shallow soil. He said that some well-built roofs can retain as much as 60% of light rainfall.

JB: Beattie also said that green roofs release excess water slowly – so urban runoff becomes more manageable. Plants and soils on a rooftop help filter out pollutants, so rainwater runoff is cleaner. Green roofs help insulate the building below, while providing habitat for birds. And they help lessen the “heat island” effect whereby urban areas are hotter than the surrounding countryside.

DB: We have links to more about green roofs at earthsky.org. Our thanks to the National Fish and Wildlife Foundation – promoting the conservation of native fish, wildlife, plants, and their habitats. We’re Block and Byrd for Earth & Sky.