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What is the urban heat island effect?


Techniques to Reduce the Urban Heat Island Effect
Green roofs, like this one atop Chicago's City Hall, help offset the urban heat island effect.
Green roofs, like this one atop Chicago's City Hall, help offset the urban heat island effect.
Tim Boyle/Staff/Getty Images

Luckily, since we know what causes the urban heat island effect, we can control it to a significant extent. Certain techniques reduce the demand for air conditioning and reduce energy bills.

Because the dark surfaces and low albedo of urban structures heat the area, the logical solution would be to reverse this trend. Urban planners may do this by painting structures white, or other light colors. This basic technique goes a long way in reversing the urban heat island effect.

However, some people don't like the idea of a glaring, all-white city. Low-reflectivity coating offers an alternative and comes in non-white colors. These kinds of coatings reflect invisible radiation without reflecting all light [source: Synneffa]. So, they keep an object relatively cool without sacrificing its dark color.

Certain high-reflectivity coatings can also be applied to asphalt. Asphalt chip seals and emulsion sealcoats are two such examples that treat asphalt to make its surface more reflective [source: EPA]. The processes reduce the albedo factor of asphalt, which is a major contributor to the urban heat island effect.

One fad that's gaining popularity is the installation of green roofs atop city buildings. This solution doesn't have anything to do with color. A "green roof" is simply a roof that includes plants and vegetation. Green roofs harness the same evaporative cooling effect that cities lose when they hack away vegetation. So a green roof not only prevents the building's roof from absorbing heat, but cools the air around it, offsetting the urban heat island effect to an extent. Many sustainable buildings use green roofs to reduce their reliance on energy consumption.

Several other methods help reduce the urban heat island effect as well. For instance, roof sprinkling is another evaporative cooling solution. Sprinklers on the roof wet the surface so that the air around it cools through evaporation [source: Asimakopoulos]. Urban planners also set up traditional parking lots along lots where trees and vegetation grow. Tall trees not only contribute to evaporative cooling but also provide much-needed shade.

To learn more about green-building techniques and related subjects, explore the links on the next page.


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