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Heat Island Effect

Heat Island Reduction Initiative (HIRI) Graphic Depicting Heat Island Curve and HIRI Logo

The term "heat island" describes built up areas that are hotter than nearby rural areas. The annual mean air temperature of a city with 1 million people or more can be 1.8–5.4°F (1–3°C) warmer than its surroundings. In the evening, the difference can be as high as 22°F (12°C). Heat islands can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality, and water quality.

Communities can take a number of common-sense measures to reduce the effects of summertime heat islands. This website provides information on the heat island effect, its impacts, and the strategies that communities can take to reduce urban temperatures. Of the information available to communities, key EPA resources include a compendium of mitigation strategies, a community action database, and regularly scheduled webcasts.

Basic Information - Learn about urban heat islands, why they are important, and how they are measured.

Where You Live - Find information on heat island mitigation activities in your state or community.

Heat Island Impacts - See how urban heat islands affect energy use, air quality, human health, and water quality.

Heat Island Mitigation - Discover how communities can reduce urban temperatures through energy-saving strategies that provide multiple benefits.

Resources - Browse a collection of publications, tools, related links, and presentations from national heat island webcasts.

Glossary - Find definitions of the technical terms used on this site.



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