“If 20 percent of urban areas are covered with impervious surfaces,” says Groffman, “then that also means that 80 percent is natural surface.” Whatever is going on in that 80 percent of the country’s urban space — as Groffman puts it, “the natural processes happening in neighborhoods” — has a large, cumulative ecological effect.
This is right, although 20% is a very low number. Even in the suburbs, I would expect streets alone to be 20%, and driveways and parking lots to add a lot more. There are a lot more impervious surfaces than just buildings. In dense urban areas, it can be 75% or more. Still, even in the densest areas, there is still a lot of space left over that we pretty much write off as an ecological dead zone, when it doesn’t have to be that way.
(Source: The New York Times)