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Urban Heat Island Effect Makes Cities Hotter Than Rural Areas

Linda Hardesty

heat island energy manageThe urban heat island (UHI) effect is caused by dark, impermeable surfaces, making urban temperatures several degrees hotter than those in surrounding areas, causing the need for more air conditioning.

On average, UHIs make cities 7°F hotter than surrounding rural areas, according to a report from the American Council for an Energy Efficient Economy and Global Cool Cities Alliance.

For the report “Cool Policies for Cool Cities: Best Practices for Mitigating Urban Heat Islands in North American Cities,” the researchers conducted a review of the UHI mitigation activities of 26 North American cities and distributed a questionnaire to local government contacts to gather information.

There are three main causes of the urban heat island effect: i) dark surfaces, ii) lack of vegetation, and iii) population density. Two of those causes – dark surfaces and lack of vegetation – can be mitigated through policies related to buildings and city planning. Installing reflective and lighter-colored surfaces on city roadways, walkways, and roofs is a primary UHI mitigation strategy. The EPA reports that conventional asphalt pavement can reach summertime temperatures of 120-150°F. In contrast, a “cool” pavement can be 50-70°F cooler.



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