Magazine article American Forests

Atlanta's Changing Environment

Magazine article American Forests

Atlanta's Changing Environment

Article excerpt

Nationwide, cities are grappling with the growth of so-called heat islands and the effects of a changing landscape on local ecosystems. There may be no better example of a community in transition than Atlanta - a mid-sized southern city turned regional hub for business and industry.

Working with federal and state partners, AMERICAN FORESTS has spent the last couple of years developing a comprehensive yet practical way to map Atlanta's ecology and analyze the benefits trees provide. Our goal: Give residents the tools they need to put a dollar value on natural resources and include those resources in land-use planning decisions. We wanted to go beyond emotions and aethetics to determine if changes in temperature, stormwater flow, water quality, and energy use are directly attributable to the changes in Atlanta's landscape.

Using data from an orbiting Landsat satellite, we mapped the city's development from 1972 through 1993. The results were stunning: About 65 percent of what had been trees and forests is now part of the built environment. The most obvious change is the decline in the natural landscape - the thick tree canopy, which appears in green on the maps shown here - and an increase in urban infrastructure, which appears in black. The red and yellow indicate a mixture of trees and buildings.

The price of progress, you say? Consider this: When weather data is added to the analysis, it shows Atlanta is heating up at an alarming rate. Downtown and airport temperatures can soar up to 12 degrees higher than the surrounding treed areas. These hotter temperatures - which will be felt this summer in the downtown Olympic venues - produce more air pollution, reduce water quality, and result in more expensive summer cooling bills. If Atlanta has an average summer, the Olympic athletes will go for the gold in the hottest games ever.

These changes have come on gradually as the city center and the resulting "heat island" have gotten more built up and more spread out. In 1972 temperatures in the hottest part of downtown were 6 to 9 degrees higher than in the surrounding countryside. Today not only has the temperature increased, the hot center has tripled in size. Temperatures at Hartsfield International Airport, which in 1972 were 3 to 6 degrees higher than the surrounding countryside, now are 9 to 12 degrees higher.

Urban heat islands do more than just make us uncomfortable. They affect the quality of the air and strain the resources of local utility companies, which in turn can cause brown-outs and force utilities to mobilize old, inefficient power-generating equipment. The thousands of urban heat islands that are our cities may contribute to larger climate trends, including the granddaddy of all - global warming.

Our measurements also turned up a disturbing possibility: Atlanta may be creating some of its own weather problems. The heat island's elevated temperatures appear to be causing a low pressure area that produces air movement into the city center, trapping hot air and pollution.

Scientists recognize urban heat islands as a source of many environmental and energy consumption problems. Studies at California's Lawrence Berkeley Laboratory show that about 30 percent of a city's air pollution problems are directly related to increased temperatures. Heat produced by a rock-like city center makes the city hotter, and dark surfaces and sparse vegetation make it worse.

Compounding the problem, for every 1-degree increase in temperature over 72 degrees Fahrenheit, the possibility of smog - a mixture of sulphur and nitrogen - increases by 6 percent, according to Lawrence Berkeley Lab scientists.

Cities can shrink their heat islands by good planning and innovative construction techniques; keeping more tree cover and using light, rather than dark, colors on built surfaces. AMERICAN FORESTS' Cool Communities program identifies many positive actions a community can take (see A Cooling Trend, at right). …

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