BEIJING, Sept. 18 (Xinhuanet) -- In a Midwestern county in the United States suburban parking spaces outnumber drivers by three to one, a finding that reveals a trend nationwide that increases pollution and urban heating, researchers say.

    Digitalized aerial surveys taken in 2005 were used to determine the total area devoted to parking lots in Indiana's Tippecanoe County. The photos showed the paved lots covered an area larger than 1,000 football fields and there were three times as many parking spaces as drivers who lived in the county, said study leader Bryan Pijanowski of Purdue University.

    Pijanowski said his study was relevant nationwide because generally Americans are paving an increasing amount of land each year on which to park when they go to work, shopping, school or other places.

    The results of the Tippecanoe study are cause for concern because parking lots are a major source of water pollution, contributing 1,000 pounds of heavy metals into water runoff every year, he said.

    "The problem with parking lots is that they accumulate a lot of pollutants — oil, grease, heavy metals and sediment — that cannot be absorbed by the impervious surface," said study member Bernard Engel. "Rain then flushes these contaminants into rivers and lakes."

    Because parking lots also prevent the rain from soaking into the ground, they can worsen local flooding and erosion, Pijanowski said.

    The paved surfaces also add to the urban heat island effect, which can raise temperatures by 2 to 3 degrees Celsius by absorbing more of the sun's rays than the surrounding ground, said Indiana state climatologist Dev Niyogi, a colleague of Pijanowski at Purdue who did not work directly on this study.

    Pijanowski suggests that businesses such as "big box" retailers and mega-churches could construct shared lots to help conserve land and stave off some of the parking lots' negative effects.

    (Agencies)