U.S. streets, parking lots, buildings would cover Ohio

BOULDER, Colorado, June 15, 2004 (ENS): The combined size of all highways, streets, buildings, parking lots and other solid structures within the lower 48 states and the District of Columbia is some 43,480 square miles, roughly the size of the state of Ohio.

The finding comes from a study by Christopher Elvidge of the National Oceanic and Atmospheric Administration's National Geophysical Data Center in Boulder, Colorado, who along with colleagues from several universities and agencies produced the first national map and inventory of impervious surface areas in the United States.

The study appears in the June 15 issue of "Eos," which is published by the American Geophysical Union.

The researchers note the new map is important because impervious surface areas affect the environment.

The qualities of impervious materials that make them ideal for construction also reduce heat transfer from Earth's surface to the atmosphere, creating urban heat islands.

In addition, the replacement of heavily vegetated areas by impervious surface areas reduces sequestration of carbon, which plants absorb from the atmosphere.

Both effects can play a role in climate change.

Within watersheds, impervious surface areas alter the shape of stream channels, raise the water temperature, and sweep urban debris and pollutants into aquatic environments.

These effects are measurable once 10 percent of a watershed's surface area is covered by impervious surface areas, Elvidge says.

An increase in impervious surfaces means fewer fish and fewer species of fish and aquatic insects, as well as a general degradation of wetlands and river valleys.

The researchers found the impervious surface area of the Lower 48 states is already slightly larger than that of its wetlands, which cover 38,020 square miles.

Elvidge notes that few areas have impervious surface area maps, because they are difficult and expensive to create.

He used a variety of data sources to produce the map accompanying his article, including nighttime lights observed by satellite, Landsat images, and data on roads from the U.S. Census Bureau, along with aerial photography.

The map should provide a useful benchmark to track the growth of impervious surface areas, in particular because the U.S. population is increasing by some three million people each year. In addition, roughly one million new single family homes and 10,000 miles of new roads are added annually.


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