Before human development began disturbing
natural habitats, soil and vegetation
constituted part of a balanced ecosystem that
managed precipitation and solar energy effectively.
In natural areas, much of the rainwater
infiltrates into the ground or is returned
to the atmosphere via evapotranspiration,
thus absorbing rainwater and performing
a cooling function for excess solar loads. As
the human population began expanding,
more construction ensued, which disturbed
these natural habitats. Cities, towns, and
suburbs all add more impervious surfaces as
we construct buildings, roads, and parking
lots. In the United States, it is estimated that
10% of residential developments and 71% to
95% of industrial areas and shopping centers
are covered with impervious surfaces (Ferguson,
1998). Today, two-thirds of all impervious
area is in the form of parking lots,
driveways, roads, and highways (Water Resources
Group, 1998), and this loss of natural
areas causes many problems.