HOT ZONES: URBAN HEAT ISLANDS

Climate Central developed an Urban Heat Intensity Index for 159 U.S. cities, finding that New Orleans, Newark, New York City, Houston, and San Francisco have the highest intensity scores. The report identifies albedo, lack of greenery, population density, and building height as primary drivers of the UHI effect. These conditions exacerbate heat waves, worsen air quality through ground-level ozone formation, and disproportionately affect vulnerable populations, particularly those in formerly redlined neighborhoods. Proposed solutions include short-term emergency cooling measures and long-term infrastructure changes such as planting trees, installing green and cool roofs, and deploying solar energy.

• Climate Central's Urban Heat Intensity Index, applied to 159 U.S. cities, identifies New Orleans as having the highest score (8.94°F), followed by Newark, N.J., New York City, Houston, and San Francisco. The index measures the potential temperature difference between a city and its less developed surroundings, with scores ranging from less than 5°F to nearly 9°F.
• The intensity of urban heat islands is driven by five primary factors, ordered by their level of contribution: albedo, percentage of greenery, population density, building height, and the average width of streets and city irregularity.
• Urban heat islands compound the effects of climate change by increasing the frequency and intensity of extreme heat events. While climate change is a global phenomenon, UHIs are local effects caused by development, loss of vegetation, and the increase of impermeable surfaces.
• Extreme urban heat significantly impacts public health and air quality. It is the leading cause of weather-related deaths in the U.S. over the last 30 years and contributes to the formation of ground-level ozone and the trapping of pollutants through atmospheric stagnation.
• Heat-related impacts are distributed unequally, with low-income communities and people of color facing disproportionate risks. Research indicates that neighborhoods with higher UHI intensity often overlap with areas previously subjected to race-based redlining practices.
• Increased demand for cooling during heat events strains the electric grid and creates a feedback loop where air conditioners dump heat into the atmosphere and contribute to carbon dioxide emissions, as 60% of U.S. electricity is still generated from fossil fuels.
• Effective long-term mitigation strategies include planting trees to reduce peak summer temperatures by 2–9°F, implementing green roofs, and using cool roofs. Solar panels are also noted for providing shade and reducing the heat island effect while displacing fossil fuel-based electricity.

APA

Climate Central (2021). HOT ZONES: URBAN HEAT ISLANDS. https://assets.ctfassets.net/cxgxgstp8r5d/1XZZjkLYwtcmKL5k3wEinl/5f8c9b5b2d8dd56e1bda7f51278fc3d2/2021_UHI_Report.pdf

Chicago

Climate Central. HOT ZONES: URBAN HEAT ISLANDS. 2021. https://assets.ctfassets.net/cxgxgstp8r5d/1XZZjkLYwtcmKL5k3wEinl/5f8c9b5b2d8dd56e1bda7f51278fc3d2/2021_UHI_Report.pdf.

Wikipedia

{{cite report |author=Climate Central |title=HOT ZONES: URBAN HEAT ISLANDS |date=14 July 2021 |url=https://assets.ctfassets.net/cxgxgstp8r5d/1XZZjkLYwtcmKL5k3wEinl/5f8c9b5b2d8dd56e1bda7f51278fc3d2/2021_UHI_Report.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{climatecentral2021hot, author = {{Climate Central}}, title = {{HOT ZONES: URBAN HEAT ISLANDS}}, institution = {Climate Central}, year = {2021}, month = jul, url = {https://assets.ctfassets.net/cxgxgstp8r5d/1XZZjkLYwtcmKL5k3wEinl/5f8c9b5b2d8dd56e1bda7f51278fc3d2/2021_UHI_Report.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }