People and Heat Islands

A group of young children in red and blue jerseys run across a playground.

Heat affects everyone. Due to the heat island effect, people who live in cities are more at risk than those in suburban or rural areas. What’s more, some areas within a city are often hotter than others. These neighborhood-level hotspots are called “intra-urban” heat islands. Intra-urban heat islands are caused by the uneven, inequitable spread of landcovers in the urban landscape, leading to more heat-absorbing buildings and pavements and fewer cool spaces with trees and greenery.

Residents of intra-urban heat islands are more likely to experience heat-related illnesses and even death. Related negative effects include worse air quality and a higher cost burden of air conditioning bills.

This page explores the reasons behind these inequities, their trends and consequences, and solutions.

On this page:

Why are heat islands inequitable?
What are the health consequences of heat islands and inequity?
What are the financial inequities created by heat islands?
How can local governments effectively address heat inequity?
What are examples of city heat equity programs?

A young, Black family of three sits on a bench and eats ice cream. Their small dog watches them.

Why are heat islands inequitable?

Researchers have found that intra-urban heat islands are often linked to demographic factors such as income and race. An EPA review of several studies found that some communities in the United States, particularly those that are low-income and with higher populations of people of color, have neighborhoods with higher temperatures relative to adjacent neighborhoods in the same city. The studies identify historic redlining as a contributing factor. Specifically, people of color and community members with low incomes are more likely than other groups to live in historically redlined neighborhoods that are present-day intra-urban heat islands.

What are the health consequences of heat islands and inequity?

The hotter conditions of heat islands and demographic inequities intersect with other risk factors. In particular, air quality worsens on hot, sunny days. A reaction between sunlight and air pollutants forms more ground-level ozone, or smog. Asthma is more common among some communities of color and low-income households than the general population, putting these populations at greater risk from hotter temperatures, air pollution, and the smog formed under these conditions.

What are the financial inequities created by heat islands?

Excessive heat is a financial burden for many people, especially low-income households. For instance, about 27 percent of all U.S households report that they have difficulty paying energy bills or that they are unable to cool their homes due to cost concerns.ⁱⁱⁱ Low-income households also tend to live in less energy-efficient homes that are more expensive to cool.^iv The inability to afford household energy needs, or “energy insecurity,” makes it harder to stay cool, comfortable, and healthy during periods of extreme heat.

Heat Dome in Portland, OR

In the summer of 2021, areas of the Pacific Northwest reached record high temperatures over a series of several days. Portland, OR, reached a record-high temperature of 116°F, which is 42°F above normal.^v That week, Portland area health clinics and hospitals reported heat-related visits more than three times above average.^vi The “heat dome,” as the event became known, killed dozens of people in Portland alone—and hundreds across the region. Before that year, heat-related deaths were virtually unheard of in the area.

According to the county’s official report on the impacts of the heat dome, 61% of the people who died lived in intra-urban heat islands. The majority of the people who lost their lives did not have working air conditioning.

How can local governments effectively address heat inequity?

Heat inequities can be resolved through programs and policies designed to target historically underserved and overburdened people to reduce their relative heat risk. Below are successful approaches that local governments have used to protect residents who are most at risk from extreme heat. Click on each approach to learn more.

Incorporate principles of environmental justice: Increasing public investment in underserved neighborhoods is an important way to resolve heat inequity. This includes targeted heat island reduction activities in neighborhoods where people of color and people with low incomes live—such as tree planting campaigns and financial incentives for green roofs.

Engage community members in decision-making: Community buy-in is key for long-term success of government initiatives. Learn how the City of Philadelphia, PA is incorporating equity into community engagement around heat reduction.

Use trusted messengers in outreach and messaging campaigns: To better ensure that information reaches residents, engage trusted community members early—such as community advocacy groups, healthcare providers, or religious leaders—to effectively shape and communicate messages. Learn how to develop an effective engagement strategy for local environmental projects.

Meet your audience where they are: Translate messages into languages spoken by your target audience. Distribute information in popular places such as supermarkets, transit hubs, and places of worship. Use plain language and wording that will connect with your audience; for example, refer to communities or individuals as “at-risk” rather than “vulnerable.” Learn about strategies for cross-cultural and multilingual communication.

Collect relevant data: To design equitable heat solutions, governments should identify and track which neighborhoods represent the most intense heat islands and which residents have the highest risk of heat exposure. For example, view the heat vulnerability map of Charleston, SC.

Structure programs to be widely accessible: Individual circumstances—such as lower incomes, lack of personal transportation, lack of childcare support, and non-traditional work hours—can limit a person’s ability to take advantage of programs. To address this, some localities provide grants or low-interest loans instead of rebates for green or cool roofs, to reduce upfront installation costs. For example, New York City, NY provides grants for green infrastructure projects.

Design programs to benefit renters: Heat reduction strategies often involve modifying property, which can prevent renters from reducing their heat exposure. To help, governments can create financial incentives that motivate property owners to install strategies such as green roofs. Learn more about energy solutions for low-income communities.

What are examples of city heat equity programs?

In recent years, many cities have launched initiatives to reduce heat inequities and assist residents with the fewest resources. By incorporating equity into heat island policies and planning, these governments help create more livable cities for everyone.

Newark and Camden, NJ and Baltimore, MD: These three cities have prioritized community engagement and nonprofit partnerships to increase trees on private property and cool heat islands in an equitable way. For example, Newark’s Office of Sustainability uses the i-Tree tool to prioritize underserved neighborhoods for planting. Similarly, TreeBaltimore, a community-based organization, created a street tree inventory that informed the city’s planting map. Leaders of the three cities cite the importance of community outreach for reaching their goals.

Boston, MA: A citywide heat plan includes 26 strategies to protect residents, with a particular focus on five communities that experience hotter temperatures. These include a citywide cooling network (e.g., cooling centers and outdoor heat relief spaces), increased shade on municipal sites, and home energy retrofits.

San Antonio, TX: A unique program called Under 1 Roof helps low-income households install cool roofs, which reduce indoor temperatures and help save on energy costs.

Los Angeles, CA: Cool pavements have been installed at several locations to keep structures and residents cooler. The Cool LA program aims to bring 250 lane miles of cool pavement and nearly 2,000 trees to Los Angeles’ hottest residential areas, which are more densely developed and predominantly lower-income.

Cincinnati, OH: Cincinnati's Urban Tree Canopy Assessment Fund allows the city to conduct periodic urban tree canopy analyses which inform sustainability efforts in neighborhoods. Cincinnati's goal is to reach a minimum of 40% tree canopy coverage in each residential neighborhood, and it gives residents in areas with less than 40% coverage priority access to tree giveaways. Cincinnati Trees and Equity Case Study (pdf) (648.54 KB) .

City and county government agencies: Innovative communication strategies are informing underserved and overburdened groups of the risks of extreme heat and offering ways to keep safe during the hottest days, as highlighted by a national EPA competition.

Selected Bibliography

Chakraborty, T., A. Hsu, D. Manya, and G. Sheriff. 2019. Disproportionately higher exposure to urban heat in lower-income neighborhoods: a multi-city perspective. Environmental Research Letters 14 (10): 105003.

Chakraborty, T., A. Hsu, D. Manya, and G. Sheriff. 2020. A spatially explicit surface urban heat island database for the United States: Characterization, uncertainties, and possible applications. ISPRS Journal of Photogrammetry and Remote Sensing 168: 74-88.

Dialesandro, J., N. Brazil, S. Wheeler, and Y. Abunnasr. 2021. Dimensions of Thermal Inequity: Neighborhood Social Demographics and Urban Heat in the Southwestern U.S. International Journal of Environmental Research and Public Health 18 (3): 941. 10.3390/ijerph18030941.

Gerrish, E., and S.L. Watkins. 2018. The relationship between urban forests and income: A meta-analysis. Landscape and Urban Planning 170: 293-308.

Hoffman, J.S., V. Shandas, and N. Pendleton. 2020. The Effects of Historical Housing Policies on Resident Exposure to Intra-Urban Heat: A Study of 108 US Urban Areas. Climate 8 (1): 12.

Hsu, A., G. Sheriff, T. Chakraborty, and D. Manya. 2021. Disproportionate exposure to urban heat island intensity across major US cities. Nature Communications 12 (1): 2721.

Li, D., G.D. Newman, B. Wilson, Y. Zhang, and R.D. Brown. 2022. Modeling the Relationships Between Historical Redlining, Urban Heat, and Heat-Related Emergency Department Visits: An Examination of 11 Texas Cities. Environment and Planning B: Urban Analytics and City Science 49(3): 933–952.

McDonald, R.I., T. Biswas, C. Sachar, I. Housman, T.M. Boucher, D. Balk, D. Nowak, E. Spotswood, C.K. Stanley, and S. Leyk. 2021. The tree cover and temperature disparity in US urbanized areas: Quantifying the association with income across 5,723 communities. PLOS ONE 16 (4): e0249715.

Mitchell, B.C., and J. Chakraborty. 2018. Exploring the relationship between residential segregation and thermal inequity in 20 U.S. cities. Local Environment 23 (8): 796-813. 10.1080/13549839.2018.1474861.

Wilson, B. 2020. Urban Heat Management and the Legacy of Redlining. Journal of the American Planning Association 86 (4): 443-457.

Zhou, Weiqi, G. Huang, S. T.A. Pickett, J. Wang, M.L. Cadenasso, T. McPhearson, J. Morgan Grove, and J. Wang. 2021. Urban tree canopy has greater cooling effects in socially vulnerable communities in the US. One Earth 4 (12): 1764-1775.

Webpage References

ⁱ Chakraborty, T., A. Hsu, D. Manya, and G. Sheriff. 2020. A spatially explicit surface urban heat island database for the United States: Characterization, uncertainties, and possible applications. International Society for Photogrammetry and Remote Sensing Journal of Photogrammetry and Remote Sensing 168: 74-88.

ⁱⁱ Wilson, B. 2020. Urban Heat Management and the Legacy of Redlining. Journal of the American Planning Association 86 (4): 443-457.

ⁱⁱⁱ Energy Information Administration. 2022. In 2020, 27% of U.S households had difficulty meeting their energy needs.

^iv American Council for an Energy-Efficient Economy. 2022. Energy Burden Report.

^v Schramm, P.J., A. Vaidyanathan, L. Radhakrishnan, A. Gates, K. Hartnett, and P. Breysse. 2021. Heat-Related Emergency Department Visits During the Northwestern Heat Wave — United States, June 2021. Morbidity and Mortality Weekly Report 70 (29):1020–1021.

^vi Ehrlich, A. 2022. Exactly one year since ‘heat dome,’ Portland remembers those lost. Oregon Public Broadcasting. June 27.