Extreme Heat and Climate Change

Ana Lucrecia Rivera, GIS Assistant, Stanford Geospatial Center, NLC Silicon Valley


As the global human population increases and urban centers develop, heat emanated by anthropogenic activities and impervious surfaces cause a climatic condition known as urban heat island (UHI). Urban Heat Islands are defined as closed isotherms where a surface, usually referring to the air near the ground (canopy layer), is relatively warmer than its surroundings.[i] Usually, high temperatures are recorded at the nucleus of the city, in the most built-up core.

By transforming land cover, from natural vegetation to construction materials, shortwave energy (heat) is absorbed during the day and stored in low-albedo asphalt, concrete and glass. Building materials and proximity to one another trap warm air, making it more difficult to disperse excess heat. In addition, excessive use of air conditioners, necessary to mitigate the heat island effect, release waste heat into the atmosphere, elevating air temperatures.


Extreme heat events make cities less comfortable for living, and are associated with increased morbidity and mortality. Mapping studies have demonstrated spatial variability in heat vulnerability. A study conducted between 2000 and 2011 in New York City shows that heat waves were more likely to kill black individuals and those living in homes in census tracts that receive greater public assistance. Most important, deaths during heat waves occur more frequently among residents living in areas with low green space.[ii] Summers affect the poorest neighborhoods, with high-density housing and low vegetated surfaces where people cannot afford to turn up, or even turn on, an A/C unit.[iii] A rise in temperature also increases the concentration of organic pollutants and irritating gases. Children, the elderly and people with pre-existing respiratory conditions are most vulnerable to the negative effects of heat islands. UHI phenomenon, which generates convergence and then transports air pollutants to a metropolitan areas, increases hospital respiratory admissions in the warm center of an urban area.[iv]

According to an EPA Heat-Related Deaths report (2016), more than 9,000 Americans have died from heat-related causes since 1979.[v] In California, temperatures reached 115 degrees in the Central Valley in 2006. Police departments investigated at least 29 possible deaths due to extreme weather.

By spatially detecting UHI formations it is possible to determine what factors are causing the heat storage (city morphology-canyon effect and/or land cover) and health implications (heat mortality and reduced air quality). Results provide useful information to propose or revise building strategies and public policies to create better cities. The study of heat islands at the micro-scale level can improve the well-being of city users in the public realm and improve building energy performance. In addition, local government agencies should be able to evaluate a heat island distribution model. This would allow them to promptly apply mitigation strategies.


In 1998, the EPA — City Partnerships formed to address Urban Heat Islands in Baton Rouge, Chicago, Houston, Sacramento and Salt Lake City. City officials worked with EPA and federal researchers (NASA and LBNL) to map surface temperatures with satellites and sensors.


EPA’s Sacramento Urban Heat Island Project led to the Sacramento Cool Community Program (SCCP) that, in partnership with the Sacramento Tree Foundation, has the nation’s largest shade tree program, “Sacramento Shade.” The SCCP established five working subcommittees: 1) Trees and Vegetation, 2) Cool Roofing, 3) Cool Pavements, 4) Air Quality Impacts, 5) Outreach and Education. In addition, the Sacramento Parking Lot Shading Ordinance requires developers of new parking lots to plan to cover 50% of the lot with shade trees within 15 years.


Chicago is considered a “leading city” in heat island reduction measures. Some of the city’s measures include:

1) Landscape Ordinance, since its implementation more than 2,000 new trees and 8,000 new shrubs have been planted; 2) Energy Code, requires reflective roofs;

3) Construction of rooftop gardens in its City Hall; 4) Open Space Impact Fee Ordinance that requires developers to pay a fee or contribute a proportionate share of open space; 5) Asphalt replacement with permeable brick surfaces.

Salt Lake City

Salt Lake City works through the Utah Office of Energy Services to implement several heat island reduction measures that include demonstration projects, installation of reflective green roofs, planting shade trees, displaying cool pavements and community educational programs. The Utah Office of Energy Services created the Kool Kids Program, which educates students through the use of assembled Kool Kids Box that includes thermometers, thermal maps and infrared analyzers, about the urban heat island phenomenon and its impact on energy and air quality. [vi]

Other cities and states, like Minnesota, through their Department of Health, are creating Extreme Heat Toolkits and Population at Risk analysis to prevent heat — related illness and deaths.

Policy Recommendation

Urban Heat Island intensity and distribution vary locally; therefore, government agencies should consider different mitigation strategies that involve long-term programs. The EPA Urban Heat Island Pilot Program roadmap proves that research is a first step to locate “hotspots”. Once heat islands are assessed, effective mitigation strategies can be proposed and implemented, in partnership with non-profit organizations and businesses. This section examines mitigation and adaptation actions to reduce land surface temperature and its impacts on vulnerable populations.

Research: Allocate funding for urban climate research.

Locate: Create an urban heat island observation and monitoring system.

Legislate: Define extreme heat weather events as a natural disaster and urban heat islands as risk zones.

Plan: Elaborate an extreme “heat weather event relief and recovery policy” that considers the differences between ecoregions.

Reduce: Reduction of anthropogenic heat emission by:

1. Improving urban infrastructure and the built-up environment by:

a. Improving urban surfaces where heat islands exist by incentivizing tree planting in private parcels, public facilities and public spaces.

b. Incentivizing green roofs.

c. Subsidizing new programs for white facades and roofs.

d. Improving urban structure to ensure wind flow through green spaces by:

e. Developing a network of large green spaces.

f. Using city planning systems to develop “less environmental burden cities”

2. Improving life-style by:

a. Facilitating summer vacation to reduce anthropogenic heat emission in the cities,

b. Developing campaigns that promote light clothes in summer.

c. Implementing heat island educational programs


The UHI phenomenon reflects a wide range of social and economic activities. Therefore, partnership between the federal, state and local governments, businesses and residents is important to implement mitigation and adaptation measures. In addition, linkage with policies on global warming, urban planning, traffic relief and energy efficiency should be promoted (InterMinistry Coordination Committee, 2004).

1. Federal: Update and enforce EPA’s “Heat Island Reduction Initiative” (HIRI) from 1997, elaborated as a response to the 1995 heat wave that struck Chicago, which resulted in the deaths of over 700 people.

2. State: Environmental Protection Office to monitor and observe UHI meso-scale formation and develop a syndromic system alert and work with the California Department of Public Health.

3. Local (County and City level):

a. County Public Health Department.

b. Planning Department.

c. Parks Department.

d. Air Quality District.

e. Transportation Agency.

f. Business Groups.


Since 1979, more than 9,000 Americans have died from heat-related causes, according to the EPA. The indicator shows a peak in heat related deaths in 2006, a year known as the “2006 North American heat wave”, which spread throughout most of the United States and Canada. Impacts also include increased energy and water consumption. [vii]

EPA’s Heat Island Reduction Program “focuses on translating urban heat island research results into outreach materials, tools, and guidance to provide communities with information needed to develop urban heat island projects, programs, and policies”.[viii] It provides resources and leads activities to reduce the heat island formation. Until now, it is a voluntary initiative. However, as cities continue to grow and extreme heat weather events become more frequent, the Heat Island Reduction Program should be a multi-stakeholder effort adopted by all cities, in particular by high-density urban areas. Children, the elderly, people living on neighborhoods with few or no green space, and who cannot afford to turn on the air conditioner are the most affected by extreme heat weather events. Therefore, the reduction of heat islands is not a matter of the environment only; it is a matter of justice and democracy.

[i] Voogt, James. 2007. “How Researchers Measure Urban Heat Islands.” Department of Geography. http://epa.gov/heatisland/resources/pdf/EPA_How_to_measure_a_UHI.pdf.

[ii] Madrigano, Jaime, Kazuhiko Ito, Sarah Johnson, Patrick L Kinney, and Thomas Matte. 2015. “A Case-Only Study of Vulnerability to Heat Wave — Related Mortality.” Environmental Health Perspectives 672 (7): 672–78. doi:10.1289/ehp.1408178.

[iii] McKinnon, Shaun. 2009. “Study: Wealth Buys Rescue from Urban Heat Island.” The Arizona Republic. http://archive.azcentral.com/arizonarepublic/news/articles/2009/09/20/20090920env-heat0920.html.

[iv] Lai, Li-Wei, and Wan-Li Cheng. 2010. “Urban Heat Island and Air Pollution — An Emerging Role for Hospital Respiratory Admissions in an Urban Area.” Journal of Environmental Health 72 (6): 32–35. http://search.ebscohost.com/login.aspx?direct=true&db=aph&AN=47079755&site=ehost-live.

[v] “Climate Change Indicators: Heat-Related Deaths”. EPA. December 17, 2016. Accessed May 30, 2017. https://www.epa.gov/climate-indicators/climate-change-indicators-heat-related-deaths

[vi] “Extreme Heat Events.” MDH. April 25, 2017. Accessed May 30, 2017. http://www.health.state.mn.us/divs/climatechange/extremeheat.html#toolkit

[vii] “Climate Change Indicators: Heat-Related Deaths”. EPA. December 17, 2016. Accessed May 30, 2017. https://www.epa.gov/climate-indicators/climate-change-indicators-heat-related-deaths

[viii] “Urban Heat Island Pilot Project.” EPA. January 11, 2017. Accessed May 30, 2017. https://www.epa.gov/heat-islands/urban-heat-island-pilot-project.