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State and Local Climate and Energy Program

Heat Islands

Heat islands are characterized by urban air and surface temperatures that are higher than nearby rural areas. Heat islands form as cities replace natural land cover with pavement, buildings, and other infrastructure. Many cities and suburbs have air temperatures up to 10°F (5.6°C) warmer than surrounding areas with open land and vegetation.

Urban Heat Island Profile
Urban Heat Island Profile

Heat islands can increase energy consumption due to increased cooling needs, lead to elevated emissions of air pollutants, compromise human health and comfort, and impair water quality.

Strategies employed to reduce heat island effects not only minimize these negative impacts, but can also reduce greenhouse gas emissions. The most common strategies revolve around increasing:

  • Trees and vegetation
  • Green roofing
  • Reflective roofing
  • Cool pavements

Detailed information is available from EPA's Heat Island Reduction Program.

State Policy Options

Although cities and other local government entities typically have jurisdiction over land use planning that impacts heat islands, states can develop policies and programs to assist and complement local efforts, such as:

  • Procurement — States can procure cool technologies (e.g., reflective roofing) for government buildings and revise bid specifications to include cool products.
  • Resolutions — A state organization, such as an air quality board or planning commission, can issue resolutions stating their awareness of and interest in a heat island mitigation project, which can be the first step in getting an initiative started.
  • Green building standards — Green building initiatives can capture heat island reduction strategies, such as green roofing, preserving trees and vegetation, etc.
  • Building codes — Building codes establish standards for construction, modification, and repair of buildings and other structures. States can include cool roofing in their building codes as an energy savings measure (e.g., California's Energy Efficiency Standards for Residential and Nonresidential Buildings).
  • Air quality standards — As summertime temperatures rise, the rate of ground-level ozone formation, or smog, increases. By lowering temperatures, urban heat island mitigation strategies can help reduce ground-level ozone concentrations. EPA has developed three policies that help states to include heat island reduction strategies in their air quality State Implementation Plans (SIPs).

In addition to requiring mitigation strategies, heat islands offer a key opportunity to plan for adaptation. As the climate warms, urban heat island effects may worsen, so reducing the effects of heat islands will be an important part of state climate change adaptation strategies.

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Tools and Resources

ENERGY STAR Roof Products

ENERGY STAR qualified roof products reflect more of the sun's rays, which can lower roof surface temperature by up to 100°F and decrease the amount of heat transferred into a building. ENERGY STAR qualified roof products can help reduce the amount of air conditioning needed in buildings, and can reduce peak cooling demand by 10–15 percent.

ENERGY STAR Roofing Comparison Calculator

The ENERGY STAR Roofing Comparison Calculator Exit EPA disclaimer helps consumers estimate how much energy and money they can save by installing an ENERGY STAR labeled roof product on your home or building.

Heat Island Compendium

Reducing Urban Heat Islands: Compendium of Strategies describes mitigation measures that communities can take to address the negative impacts of urban heat islands. The compendium includes six sections: Urban Heat Island Basics, Trees and Vegetation, Green Roofs, Cool Roofs, Cool Pavements, and Heat Island Reduction Activities.

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