Cities such as Kansas City, MO, are trying to find ways to mitigate the urban heat island caused by all that concrete and asphalt. (Source: John LeCoque/Wikicommons)
According to the EPA, the yearly mean air temperature of a city with 1 million people or more can be up to 5.4 degrees Fahrenheit warmer than its surroundings. (Source: MGN photos)
(RNN) - All that concrete and asphalt in a large metropolitan area adds more than places to shop, live and dine. It increases the temperature of a city, a big deal during the summer, especially during a heat wave.
The term "heat island" refers to urban areas being hotter than rural areas. The reason for the heat difference is that "surfaces that were once permeable and moist become impermeable and dry," according to the Environmental Protection Agency.
According to the EPA, the yearly mean air temperature of a city with 1 million people or more can be up to 5.4 degrees Fahrenheit warmer than the surrounding area, with a difference as high as 22 degrees in evenings.
Surfaces such as roofs and pavement can be 50 to 90 degrees hotter than the air, and release heat into the atmosphere throughout the day, making the air over urban areas hotter and hotter as the day wears on.
These warmer urban temperatures boost energy demand, as well as the costs to keep air-conditioned buildings cool, thus increasing an area's carbon footprint and exacerbating air pollution problems.
For those having to deal with high temperatures, heat islands can increase the risk of heat-related illnesses and deaths. According to a Centers for Disease Control and Prevention estimate, 8,000 people died from excessive heat exposure in the U.S. from 1979 to 2003, exceeding deaths from hurricanes, lightning, tornadoes, flood and earthquakes combined.
When relief comes in the form of summer rain, another problem begins. Heat is transferred from the pavement to the rainwater. Pavements that are 100 degrees can boost rainwater from temperatures in the 70s to more than 95 degrees.
The warm water runs into nearby streams, rivers and lakes - adversely affecting the metabolism and reproduction of many forms of aquatic life, and rapid changes in temperature can be deadly.
Stopping the island effect
Urban areas battle heat islands in many different ways, including city planning that uses more tree cover and taking advantage of paving and roofing materials that stay cool.
While reducing the need for heating and cooling, thus reducing the associated air pollution, green areas such as parks, the use of greenery in landscaping and green roofs help remove air pollutants, improve water quality, reduce noise levels, create habitats for wildlife and add to the beauty of an urban area.
Green roofs have been springing up in major U.S. cities. A green roof system takes an existing roof and adds a "high quality water proofing and root repellant system, a drainage system, filter cloth, a lightweight growing medium and plant," according to Green Roofs for Healthy Cities.
Depending on the technology used, cool roofs and pavements may actually extend the lives of the surfaces in addition to reducing the heat absorption that triggers heat islands.
Differing levels of government have used voluntary and mandatory programs to deflect urban heat islands.
Kansas City, for instance, is participating in the pilot of the EPA's Sustainable Skylines, a partnership with public and private entities. The partnership aims to reduce emissions while boosting solar energy and the use of environmentally friendly tactics to "improve the environment and strengthen the economy of the Kansas City area for both the short- and long-term," according to John B. Askew, EPA Region 7 administrator.
Philadelphia in 2010 began requiring new construction to use white roofing or those rated as highly reflective, with few exceptions.
California, in response to the energy challenges that led to rolling blackouts in 2001, has made cool-roof provisions mandatory for new non-residential building projects for roofs of more than 2,000 square feet.
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