U.S. impervious cover area approaches the size of Ohio A recent study estimates that the total impervious surface area (ISA) – streets and roads, rooftops, parking lots, etc. – within the contiguous United States adds up to about 112,610 square kilometers, almost the size of the state of Ohio. In addition, this number was found to be slightly larger than the area covered by wetlands in the lower 48 states. The study appears in the June 15 issue of "Eos," a publication of the American Geophysical Union. The findings come from work done by Christopher Elvidge of the National Oceanic and Atmospheric Administration's National Geophysical Data Center in Boulder, Colo. Using a number of data sources, Elvidge and others produced a national map and an inventory of impervious surface areas in the United States. The article lists a number of effects ISA has on the environment. ISA alters the shape of stream channels, raises the water temperature, and sweeps urban debris and pollutants into aquatic environments. It also increases the frequency and magnitude of surface runoff events. These effects lead to reduced biodiversity and degradation of wetlands and riparian zones. According to the article, these effects are measurable once impervious surfaces cover 10 percent of a watershed's surface area. Elvidge notes that few areas have ISA maps due to technical challenges and cost constraints. The study's data will be useful to those who have an interest in the impacts of impervious surface cover on water quality, riparian resources and habitat protection. With the population of the U.S. growing at rate of 3 million people per year, and 10,000 miles of new roads being constructed annually, Elvidge expects that ISA will become a more prominent environmental and growth management issue in the future. For more information, contact Christopher D. Elvidge, NOAA National Geophysical Data Center, at chris.elvidge@noaa.gov.

Colorado NPS Connection, Summer 2004