Studies find sprawl exacerbates drought, threatens farmlands. (Environmental Intelligence).

The rapid spread of sprawling suburbs in the United States is substantially limiting the amount of water that can filter into the soil to recharge aquifers and provide underground flows to rivers and lakes, according to a new report by American Rivers, the Natural Resources Defense Council (NRDC), and Smart Growth America.

The report estimates that billions of gallons of water in U.S. metropolitan areas are washed away each year due to the rapid growth of impervious, paved-over areas resulting from car-centered development. Transportation-related surfaces--including roads, parking lots, and driveways--account for more than 60 percent of impervious areas in suburban communities. Commercial parking lots constitute a large share of the problem, according to the report: "a one-acre parking lot produces 16 times more runoff than an undeveloped meadow."

The study examined the 20 most sprawling metro areas in the country and estimated the imperviousness of new development in each region, factoring in soil types and rainfall patterns. In Atlanta, the U.S. city leading the way in sprawl, suburban growth that has occurred since 1982 causes 57 to 133 billion gallons of precipitation to run off into streams and rivers each year. The amount of water lost in Atlanta alone could supply between 1.5 and 3.6 million people with water for a year. Boston, which lost 433,000 acres to sprawl between 1982 and 1997, loses between 44 and 102 billion gallons of water each year. Other cities with the highest rates of sprawl and water loss are Washington, D.C., Houston, Texas, and Philadelphia, Pennsylvania.

More than a third of Americans depend on wells and ground water for their drinking water. With rapidly growing paved-over and built-up area, however, large amounts of water are being washed down storm drain systems rather than filtering into the soil to recharge aquifers and provide underground flows to rivers and streams. "As overdevelopment washes more rainwater away instead of replenishing the water table, drought conditions get worse," warned Deron Lovaas of NRDC.

Another study, conducted by the Washington, D.C.-based American Farmland Trust, found that the United States is losing two acres of farmland every minute, mostly due to urban sprawl. Between 1992 and 1997, cities and their suburbs paved over more than 6 million acres of agricultural land-an area the size of the state of Maryland.

"The scary part is that we're losing our quality farmland--the land best suited for growing food-the fastest," said the trust's president, Ra1ph Grossi. While less than one-fifth of the agricultural land in the United States is high quality, the most fertile farmland is being paved over 30 percent faster than less-productive land.

The report found that more than 85 percent of U.S. fruits and vegetables is grown near urban areas, and is threatened by the fast-paced growth of sprawl. While the U.S. population increased by 17 percent from 1982 to 1997, urban land grew by 47 percent. And the per-capita acreage for new housing has almost doubled in the past 20 years, finds the report. Houses on 10-acre or larger lots are responsible for 55 percent of the sprawl into farmlands since 1994.

According to the report, Texas led the country in destroying its farmland. The state paved over 332,800 acres of "prime" farmland between 1992 and 1997. Ohio, Georgia, and North Carolina followed, each having lost around 200,000 acres.

Both reports call for more effective urban planning and utilizing "smart growth" principles to concentrate development in already urbanized areas. These include promoting compact building designs, preserving open space and farmlands, and zoning communities for mixed uses (interweaving commercial and residential property uses, for example) to promote walkable neighborhoods with a variety of viable transportation options.

The Farmland Trust also recommends expanding conservation programs and more effectively targeting them. Farmlands, managed appropriately, provide important habitat for wildlife and help filter and clean water supplies, as well as recharge groundwater supplies. "We must support effective planning and smart growth to steer development away from our best farmland," said Grossi. "And we must target conservation funds to our best, most threatened agricultural areas."