What’s wild about Chicago?
Landsat 5 true-color image of Chicago, taken September 10, 2010. Patches of green forest and woodlands stand out against the grey and white roads and buildings in the metro area. Light colored silt and sediment swirl in the dark blue Lake Michigan waters. To the west, a patchwork of farm fields is evident in shades of green to tan.
Know Your Earth 2.0: Chicago Wilderness
› Download larger image with scale bar (26.5 MB jpg)
The Chicago Wilderness
consists of 370,000 acres of protected lands and waters interwoven throughout the Chicago metropolitan area and stretching from southeastern Wisconsin to northwestern Indiana. The project is an alliance of conservation groups dedicated to preserving and restoring green spaces at risk of being lost to urbanization.
At the start of this conservation effort in 1996, NASA and the United States Geological Survey's Landsat
satellite images were used to establish a baseline vegetation map for the region.
Because the Landsat data record dates back to 1972, people can examine how cities have grown through time and use that information to understand causes and consequences of urban growth patterns.
Land-cover maps of the Illinois counties of Chicago Wilderness in 1972, 1985, and 1997, courtesy Y.Q. Wang, University of Rhode Island. In these images, red areas indicate buildings and roadways, and various shades of green are natural habitat and plants other than farmland. Yellow is farms and blue is water. The reduction in the extent of natural areas is clearly evident over time.
› Larger version of 1972 image (13.6 MB jpg)
› Larger version of 1985 image (13.3 MB jpg)
› Larger version of 1997 image (14.1 MB jpg)
In the case of Chicago, scientists looked back in time to see how fast the city expanded compared to population growth. They found that poor development planning was more damaging to the green space than population growth: between 1970 and 1990 developed land increased by 49 percent though the population increased by only 4 percent.
Researchers have studied how urban growth progresses and what sorts of open spaces and types of natural habitats have been preserved in many other areas around the world as well, and are finding some trends similar to what was found in Chicago. In a report
released by the non-partisan Lincoln Institute of Land Policy in January 2011, researcher Shlomo Angel and colleagues used Landsat data to look at the urban expansion of 120 international cities during the decade spanning from 1990 to 2000. They found that urban expansion grew twice as fast as population.
On the east coast, urban growth patterns and other changes to the landscape are affecting the health of the Chesapeake Bay, the largest estuary in the United States. Though the Bay produces about 500 million pounds of seafood every year, it’s a small fraction of harvests in years past. The amount of forest cover, farm fields, and urban and suburban areas directly affects the amount of pollution that enters the Bay, and also determines how well green spaces can offset the problem. But getting a handle on the total amount of change for a watershed that encompasses 64,000 square miles and the entire Baltimore-Washington, D.C. metropolis can be challenging. Space-based observations offer a more comprehensive picture.
The United States Geological Survey (USGS) partnered with the National Aeronautic and Space Administration and the National Oceanic and Atmospheric Administration to collect and analyze images of the Bay watershed taken by Landsat satellites during 1984, 1992, 2001 and 2006. The Chesapeake Bay Program
is using these data in its watershed model to help set pollution limits for the Bay and its rivers.
Cities can also affect weather patterns, including changes to rainfall and the “urban heat island effect,” a complex phenomenon that drives temperatures of cities to be higher than their surrounding landscapes.
A new method for comparing cities, developed by a team of NASA scientists, uses Landsat satellite maps of impervious surface area (surfaces that don't absorb water easily, such as roads, roofs, parking lots, and sidewalks), and land surface temperature data from the Moderate-resolution Imaging Spectroradiometer, an instrument aboard NASA's Aqua
satellites. By analyzing data from thousands of settlements around the world, the NASA team pinpointed key characteristics of cities that drive the development of heat islands. Learn more
about what the scientists discovered.
Urban Heat Islands:
Landsat images of Buffalo, New York, on August 3, 2002 (top), and Providence, Rhode Island, on July 31, 2002 (bottom), showing temperature, ranging from blue (warm) to yellow (hot). White lines delineate city limits. The researchers found that Providence has a denser development pattern than Buffalo, and a greater heat island effect. About 83 percent of Providence is densely developed, whereas just 46 percent of Buffalo is densely developed. Providence has surface temperatures roughly 12.2 degrees Celsius (almost 22 degrees Fahrenheit) warmer than its surroundings, whereas Buffalo has surface temperatures just 7.2 degrees Celsius (almost 13 degrees Fahrenheit) warmer than its surroundings. http://earthobservatory.nasa.gov/IOTD/view.php?id=47704
Urban Changes in the Chesapeake Bay Region:
Land cover in the York, PA region in 1984 (top) and 2006 (bottom). Black represents medium to high-intensity urban areas and gray represents low-intensity urban areas while green represents tree canopy. http://landsat.gsfc.nasa.gov/news/news-archive/soc_0024.html
Atlanta Heat Island:
Satellite imagery of suburban (top) and urban Atlanta shows the differences in daytime heating, as caused by the urban heat island effect. http://www.nasa.gov/mission_pages/terra/news/heat-islands.html
Watch as irrigated vegetation (red) and buildings and roads (gray) of Las Vegas expand outwards from the valley. Note the level of water in Lake Meade to the east of the city. (First video clip.) http://svs.gsfc.nasa.gov/vis/a010000/a010700/a010715/index.html
Urban heat Islands affect human health and well being. http://www.nasa.gov/topics/earth/features/heat-island-sprawl.html
› Urban growth in Charlotte, NC
› Forecasting urbanization in the greater Charlotte region
› Listen to a NASA researcher talk about the urban heat island and its importance for people (top video)
› Urban Changes in the Chesapeake Bay Region
› The Chicago Wilderness