Urban Heat Island Mitigation
The urban heat island (UHI) effect occurs when urban areas are hotter than surrounding areas. This phenomenon is caused by a high concentration of dark, impervious surfaces such as roofs, walls, and roads combined with a lack of trees and green space. Tall buildings that block or slow air movement, known as urban canyons, contribute to the formation of heat islands, along with waste heat released by vehicles and air conditioning.
Heat islands are dangerous for our communities because they increase the risk of heat-related illness and death. They also make working outside uncomfortable or even dangerous and can decrease productivity and school performance. Heat islands also increase peak power demand because air conditioning systems must work harder to keep spaces cool, which makes power interruptions more likely and increases air pollution.
Studies show that low-income communities and communities of color are impacted more severely by UHIs than other neighborhoods. This is because less investment has been made in trees, parks, and infrastructure in these areas. Check out the below video by The Verge for an example of temperature disparity between neighborhoods in New York City.
Cool Roofs and Solar-Reflective Walls as Urban Heat Island Mitigation Strategies
Cool roofs and solar-reflective walls have an important role in combating UHIs. Due to their ability to reflect heat back into the atmosphere, installing reflective materials on buildings decreases the building’s surface temperature, as well as temperatures inside the building. This means that, compared to buildings with conventional roofs and walls, less air conditioning is needed to keep occupants comfortable and buildings without air conditioning stay cooler. Cool roofs and solar-reflective walls also contribute to increased solar reflectance (albedo) of a community, which can help decrease outdoor air temperatures.
Urban Heat Island Resources
Check out the resources below to learn more about urban heat islands and how communities can take action to reduce them.
CRRC Urban Heat Island Mitigation Brochure
US EPA Heat Island Reduction Program
Global Cool Cities Alliance (GCCA) Key Initiatives
Lawrence Berkeley National Laboratory Heat Island Group
American Council for an Energy-Efficient Economy (ACEEE) State and Local Policy Database
Urban Heat Island Research
Below are several recent research publications on urban heat islands, mitigation strategies, and heat disparity among communities.
Community-Informed Heat Relief: Policy Options for Addressing Urban Extreme Heat in High-Risk Communities. (2021), Georgetown Climate Center.
Cooling Hot Cities: A Systematic and Critical Review of the Numerical Modeling Literature. Krayenhoff et al. (2021), Environmental Research Letters.
Disproportionate Exposure to Urban Heat Island Intensity Across Major US Cities. Hsu et al. (2021), Nature Communications.
Hot Zones: Urban Heat Islands. (2021), Climate Central.
Perceptions of urban heat island mitigation and implementation strategies: survey and gap analysis. Wang et al. (2021), Sustainable Cities and Society.
Rx for Hot Cities: Climate Resilience Through Urban Greening and Cooling in Los Angeles. (2020), Los Angeles Urban Cooling Collaborative.
The Effects of Historical Housing Policies on Resident Exposure to Intra-Urban Heat: A Study of 108 US Urban Areas. Hoffman et al. (2020), Climate.
Urban Heat Management and the Legacy of Redlining. Wilson, B. (2020), Journal of the American Planning Association.
- Widespread Race and Class Disparities in Surface Urban Heat Extremes Across the United States. Benz, S.A. and Burney, J.A. (2021), Earth’s Future.
