Atlanta's changing environment.

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).

Good planning means looking beyond the immediate area to see the effects development has on the surrounding countryside. Does the construction work with natural systems? Does the development allow natural cycles to flow as they should or are they short-circuited? Data gathered from the Landsat satellite also shows how the change in landscape affects the region's biggest river, the Chattahoochee.

The Chattahoochee River flows into Atlanta from the hilly country north of the city. We studied the land within six miles of the river and the Chattahoochee itself in sixteenth-of-a-mile segments from Sidney Lanier, north of the city, to West Point Lake, south of the city to see how urban growth and a decrease in tree cover along the river corridor affected water quality.

Measurements were taken and the results analyzed using two statistical models. One model showed how changes in riparian areas increased flow rates; the other was used to measure water quality through the water's reflectivity. Runoff from developed areas typically causes water flow to increase - in this case by 10 percent - increasing the risk of flooding, more sediment in the water, and reduced water quality. Our first model showed that water draining from developed areas went to the same place as where the second model indicated water quality declined - in the area shown in red on the map on above, most notably where Peachtree Creek joins the Chattahoochee [ILLUSTRATION FOR PHOTO OMITTED] and flow rates have increased more than 20 percent. Our measurements of water quality indicated two types of pollutants: sediment and organic matter (sewage or fertilizer residue, for example). Problems are compounded when these pollutants are both present in the water.

As this project shows, a changing landscape does impact the local environment. The information gathered here will help the Atlanta Regional Commission - charged with coordinating growth in the metropolitan area - provide local agencies more complete data with which to make planning decisions. That's information local governments will find they need as they work to develop sustainable communities that co-exist with and benefit from the natural environment.

Good planning requires coordination between adjoining communities, respect for the benefits of natural features, and the promotion of quality development. The information in AMERICAN FORESTS' urban ecosystem analysis will give Atlanta's decisionmakers the information they need to make better decisions about growth and development.

Spurred on by groups like Trees Atlanta, Upper Chattahoochee Riverkeeper, Georgia Urban Forestry Council, and Park Pride and nonprofit programs like Cool Communities, Atlanta is taking steps to improve its growing city (see Olympic Atlanta: Sprinting Toward Sustainability, page 22). Working together, the city, individual citizens, local companies, and foundations are restoring Atlanta's green splendor and conserving its natural resources while nurturing its economic development.

RELATED ARTICLE: A COOLING TREND

Data gathered in Atlanta shows the difference trees and light-colored surfaces can make in reducing the urban heat island. The information was gathered as part of Atlanta's participation in Cool Communities. an AMERICAN FORESTS program that uses two low-tech strategies - strategically planting trees around buildings and lightening surface colors - to reduce energy demand and a community's heat island. The step-by-step methodology proves that local citizens, businesses, and community leaders can make a difference in improving their local environment.

Seven pilot communities have been participating in the Cool Communities program: Atlanta; austin, Texas; Dade County, Florida; Frederick, Maryland; Tucson, Arizona; Davis-Monthan Air Force Base, also in Tucson; and Springfield, Illinois. Now AMERICAN FORESTS is opening the program to other qualifying communities across the country, and those joining include Salt Lake City, Utah, and Andrews Air Force Base in Maryland. Oceana Naval Air Station in Virginia will join later this spring. A new brochure shows communities how to get involved and use the knowledge gained by the pilot communities.

A companion program, Global ReLeaf for New Communities, encourages developers to conserve trees and other natural features around their projects. Studies and surveys have proven that, by taking this extra step during construction, builders and developers help the environment, do their part to reduce the urban heat island, and sell homes faster.

For more information on either of these programs, contact me in AMERICAN FORESTS' urban forestry center: 202/667-3300 ext. 236.

- LINDA MALLET 

RELATED ARTICLE: BEHIND THE SCENES

Mapping urban heat islands and measuring the benefits produced by urban ecosystems requires more than high-tech equipment. It requires skilled operators, and AMERICAN FORESTS has some of the best. The team analyzing Atlanta's urban ecosystem included Chuck Watson, a Savannah electrical engineer with more than 15 years experience in remote sensing and GIS, and Chris Daniel, who directs AMERICAN FORESTS' GIS department and developed our CITYgreen software for desktop GIS. The Atlanta project partners were: AMERICAN FORESTS, the Environmental Protection Agency - southern region, Atlanta Regional Commission, USDA Forest Service, Georgia Forestry Commission, and Georgia Department of Natural Resources' Pollution Prevention Association Division.

- GARY MOLL

RELATED ARTICLE: ABOUT THE ANALYSIS

Today's growth is the foundation of tomorrow's community, and a community that can develop and still maintain the integrity of its natural landscape is more economically and socially sustainable. The challenge for Atlanta and communities like it is to understand how best to manage that growth and plan for the future. Development decisions made in one jurisdiction ultimately affect the region as a whole.

In 1991 AMERICAN FORESTS recognized the need to analyze urban ecosystems to meet land-use planning needs. Knowing of recent scientific research demonstrating the value of natural resources, we started to develop a technique for mapping and measuring urban ecosystems (see Urban Ecosystems: Breakthrough for City Green, September/October 1995). Atlanta was one of our first project sites and has become a model for demonstrating the potential of this technique.

But communities don't have to be the size of Atlanta or undertake a project of this scale to learn how best to include natural resources in land-use planning. The cost of conducting an analysis can range from $5,000 to $80,000, depending on the size of the city, the information local agencies have on hand, and the amount of time local officials can contribute to conducting the analysis.

Cities can hire AMERICAN FORESTS to conduct the analysis or, if they have existing data and the personnel to conduct ground surveys and do the analysis, they can do most of the work themselves by purchasing CITYgreen, a software package developed by AMERICAN FORESTS as a result of the techniques demonstrated here. Regardless which method is used, the benefits come back one hundredfold. For more information on the options for your city, contact AMERICAN FORESTS' urban forestry center at 202/667-3300. - GARY MOLL

Gary Moll is AMERICAN FORESTS' vice president for urban forestry. Cory Berish is senior science advisor for EPA's region 4. The opinions expressed are those of the authors and not the EPA.