Every satellite image tells a story. In the ones released Monday by NASA, the stories about Earth are not pleasant ones. Overhead views of Atlanta indicate growth there is actually creating heat and thunderstorms. And halfway around the world, in Shenzhen, China, a construction free-for-all has nearly wiped out vegetation in the city.
>NASA SCIENTISTS believe the satellite imagery can help in several ways. It could help urban planners do a better job predicting growth, and energy planners could use images of city lights at night to better understand energy use. Also, weather forecasters may be able to improve their predictions of thunderstorms.
Problems that accompany growth are among the chief complaints of city residents. Indeed, a survey released last week found that worries about sprawl and traffic have replaced crime as the top issue in the minds of American voters.
‘HOTLANTA’ CREATING STORMS
One of the fastest-growing cities in the nation, Atlanta, is “so thick with asphalt and air conditioners that it’s become a ‘heat island,’ soaking up radiant energy during the day and holding onto it at night,” NASA said in a statement summarizing several years of research.
The loss of vegetation and the addition of dark surfaces that absorb heat add to the island effect, NASA said, and because the most urban parts of the city remain warmer than surrounding areas, they essentially trap heat much like a sponge holds water.
Research suggests that the trapped heat creates a low-pressure system, with hot air rising and cooler surrounding air rushing in to replace it. That cooler air then condenses to form thunderclouds.
Indeed, weather images show that storms begin to form directly over the hottest parts of Atlanta. “As the city grows,” NASA said, “so grow the thunderheads.”
The research does not suggest, however, that this local climate change will affect the global climate because even when combined, these heat islands are just a small part of Earth’s overall size.
The scientists found that the higher temperatures of the heat islands double the occurrence of the chemical reaction that creates ozone, a major contributor to smog.
Their advice to Atlanta and similar cities: resurface roads, roofs and parking lots so that they are lighter in color, thus reflecting heat instead of absorbing it. Planting trees and other vegetation also could significantly lower temperatures, they said.
CONTRASTING GROWTH
To show how local policies and other factors affect growth, NASA contrasted what has happened in Portland, Ore., and Washington, D.C., in recent years.
The Portland data, from 1986 to 1996, show that the city has kept growth within borders defined by planners.
The Washington data, from 1973 to 1996, shows scattered growth, reflecting in part the fact that the area takes in the District of Columbia as well as cities in two bordering states.
In addition, the population in the D.C. area has grown 13 percent since 1990, NASA said, while the number of vehicles has jumped by 22 percent.
FAST FORWARD
In the case of Shenzhen, China, satellite data from 1988 to 1996 show its transformation from a small city into a metropolis in less than a decade.
A construction boom wiped out vegetation, additional sediment changed the contours of lakes and surrounding hills lost their natural features. Along Shenzhen’s coastline, construction has actually filled in parts of the bay.
The animations and data were released at the annual convention of the American Association for the Advancement of Science.