Remotely Sensing City Growth And Landscape Changes

NASA's Marshall Space Flight Center geographer Dale Quattrochi and forest ecologist Jeffery Luvall have been using Landsat data to take the temperature of Atlanta; Salt Lake City; Huntsville, Ala.; Baton Rouge, La.; and Sacramento, Calif. After the hot spots of the city have been identified, steps can be taken to cool the city's temperatures. Adding trees and grassy areas as well as replacing dark-colored roofs with light -colored ones can alter the city's temperature. A dark-colored roof in the city measures an average of 170 degrees Fahrenheit (138 degrees Celsius), while a light -colored roof measures a much cooler 70 degrees Fahrenheit (38 degrees Celsius), and forests measure 60 degrees Fahrenheit (28 degrees Celsius). "One city in the study isn't necessarily hotter or cooler than another," says Luvall.

While the asphalt and concrete building make-up of cities is basically the same, Quattrochi was able to find some subtle differences between the cities in the study. The lush vegetation in Baton Rouge is supported by the city's location near the Gulf of Mexico, but Atlanta, which is further inland, still maintains rich vegetation. "Atlanta has enough water to support its trees," says Quattrochi, "But Salt Lake City has to irrigate extensively to support its trees because the city is located in a semi-arid environment." Quattrochi added that this irrigation might possibly reduce the urban heat island effect over the city.

Pennsylvania State University meteorologist Toby Carlson has been using Landsat data to examine changes in runoff patterns as urban areas grow and change their landscape. Carlson and graduate student Traci Arthur have been using computer models that simulate land use changes that influence stormwater runoff. The study analyzes stormwater runoff over a porous surface like soil in contrast to a nonporous surface such as asphalt. Carlson also predicts the spread of urban growth in an area of abandoned strip mines where a new road is being constructed. "Some of these strip mines are grown over with vegetation, which makes them more likely to support future development than other mines that are bare," says Carlson. In the future, Carlson would like to be able to predict future runoff in developing urban areas.

University of North Carolina at Chapel Hill geographer Lawrence Band has been investigating how urbanization affects storm water runoff using satellite data plugged into computer models. The model simulations showed the differences in water quantity and quality in developed and undeveloped drainage areas. Changes in the path water takes because of roads and storm sewers causes changes in the ecosystem of the drainage basin. "Predicting how heavy rainfall or light rainfall runoff will impact the drainage basin is difficult when you factor in development, " says Band, "Using low water flow in the model, gave the best indicator of the changes between city and suburban storm water runoff, because with low waterflow, you can see more clearly where the water is draining." Band also said that the amount of water imported and exported as water supply and sanitary drainage has very significant interactions with the natural hydrological cycle.