Satellite images show effects of urban sprawl

NASA satellites captured images of changes in Atlanta's landscape from 1973 to 1997

February 21, 2000
Web posted at: 2:14 p.m. EST (1914 GMT)

WASHINGTON (CNN) -- New images from Earth-observing satellites are documenting the effects of urban sprawl on the landscape, hinting at adverse long-term consequences related to the rapid growth of cities.

NASA on Monday released satellite image sequences of Atlanta; Washington; Portland, Oregon; and Shenzhen, China.

Each provides a time-lapsed view of how the landscape in and around these cities has changed as a result of development.

The pictures show suburban Atlanta and Washington undergoing rapid deforestation as trees are cut down and roads, businesses, and houses are built. In contrast, Portland, with tight zoning laws intended to control growth, remained relatively free of the deforestation associated with sprawl.

According to NASA, 50 percent of the world's population now lives in cities -- an increase of more than 1 billion people in the last 50 years.

According to Research Atlanta Inc., the population of the Atlanta metropolitan area increased 27 percent between 1970 and 1980, and 33 percent between 1980 and 1990.

Urbanization has lead to increased traffic jams and air pollution in many cities. According to the Partnership for a Smog-Free Georgia, Atlanta experienced 68 "smog-alert" days in 1999 -- days in which the area exceeded federal guidelines for ground level ozone.

Additionally, scientists have documented a "heat island effect" in areas where vast tracts of trees have been cut down to be replaced with roads and buildings. During the hot summer months, green vegetation is no long present in these areas to absorb the heat -- which instead bakes into black asphalt and rooftops, raising temperatures as much as 5 to 10 degrees Fahrenheit.

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Other research shows crop productivity can decline significantly when urbanization and industrialization occur on an uncontrolled basis.

"Human survival depends on the ability of the landscape to produce food," NASA Goddard Space Flight Center researcher March Imhoff said in a statement.

"Food production can be fundamentally linked to primary production or photosynthesis. If the capacity of the landscape to carry out photosynthesis is substantially reduced, then the ability of the planet to support human life must also be diminished," the statement said.

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