Urban heat islands are worsening extreme temperatures in SF
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As dangerously high temperatures hit much of the U.S. this summer, urban "heat islands" are boosting temperatures in San Francisco and other major U.S. metros, a Climate Central analysis finds.
Why it matters: Urban heat islands (UHIs) — urbanized areas that experience higher temperatures due to less greenery and more infrastructure — significantly exacerbate extreme weather.
- Nearly 34 million people live in environments where UHIs could raise average temperatures by at least 8°F.
Driving the news: San Francisco ranked second behind New York City for metros with the most drastic UHI effects.
- Summer temperatures feel 9°F higher on average in San Francisco, per the analysis.
- That means people could face temperatures of 104°F when surrounding rural areas are seeing 95° temps.
- Meanwhile, 67% of the city's population live in blocks where temperatures feel at least 8°F higher.
How it works: Heat islands are created when roads, buildings, parking lots and so on "trap" heat.
- These neighborhoods tend to be lower income and lack trees and plants that would otherwise help cool the area.
The big picture: San Francisco's infrastructure, built for cool coastal temperatures, has become increasingly vulnerable to the impacts of extreme heat over the years.
- SoMa, Financial District, Tenderloin and Chinatown have some of the highest concentrations of paved surfaces in the city, contributing to the urban heat island effect.
- Many aging buildings also lack features that can help keep inside temperatures isolated, such as double-glazed windows.
Between the lines: People who live in lower-income neighborhoods and historically redlined areas suffer disproportionately higher urban heat impacts, yet are less likely to have access to air conditioning at home, work or school, the data shows.
- The housing segregation practice pushed more people of color into areas with less tree canopy cover, which can exacerbate health problems. Indigenous and Black people have higher rates of heat-related deaths nationwide, according to a 2023 KFF study.
- Columbia University found that historically redlined areas experience hotter summers than non-redlined areas in about 84% of major U.S. cities.
- Oakland was among the top cities that face the highest additional summer heat due to redlining: over 12°F compared to San Francisco's 6°F.
What we're watching: Researchers at Lawrence Berkeley National Laboratory project that by the middle of this century, temperatures in some California metros will linger in triple digits for one-third of the year.
- Cities will need to plant more trees and install cool roofs, walls and pavements to boost their resilience.
- San Francisco officials are also looking into codifying a maximum temperature threshold in the building code and addressing administrative barriers that may deter or slow extreme heat adaptations.