Heat Island Intensity
Urban heat islands form as vegetation is replaced by asphalt, concrete and other “hard” surfaces for infrastructure like roads and buildings. These surfaces absorb rather than reflect incoming heat from the sun, causing overall urban temperatures to rise. Rising temperatures increase demand for energy for air conditioning, contribute to the creation of ground-level ozone air pollution and impact our health. Recently, NASA researchers studying urban heat islands found that the type of vegetation that existed in an area before city streets and buildings appeared makes a difference in how much heating occurs – cities built in forested areas show more heating than cities built in dry, desert-like areas. Temperatures in cities like Las Vegas or Phoenix, which replaced desert, are actually lower than surrounding natural areas. Temperatures in cities like Baltimore and Atlanta, which replaced forested land, are higher.
Viewer Tip: Paved driveways, sidewalks and patios can reach up to 150 degrees Fahrenheit during summer, but new “cool” pavement techniques can help reduce the amount of heat these surfaces absorb. Using grass pavers or concrete lattices for walkways allows grass to grow in spaces between the bricks; water evaporation from the grass has a cooling effect. There are also a variety of brick pavers available in colors and materials that are designed to reflect, rather than absorb, sunlight.
Season: Summer
(Sources: NASA/Goddard Space Flight Center (January 2010). Ecosystem, vegetation affect intensity of urban heat island effect; US Environmental Protection Agency. (October 2008) “Reducing Urban Heat Islands: Compendium of Strategies.” http://www.epa.gov/heatisland/resources/compendium.htm)
