Where Is the Los Angeles Heat Island Effect Most Intense?

No, this is not a trick question. By definition, you'd think the answer is L.A., where the heat is generated, but it's actually San Bernardino, 56 miles to the east. Turns out that like ozone, heat is transported by the wind.

2 minute read

September 24, 2015, 12:00 PM PDT

By Irvin Dawid


San Bernardino

welcomia / Shutterstock

"Heat islands are created by a combination of heat-absorptive surfaces (such as dark pavement and roofing), heat-generating activities (such as engines and generators), and the absence of vegetation (which provides evaporative cooling)," according to the Urban Heat Island Index for California from the California Environmental Protection Agency (CalEPA).

Using the new index which tracks temperatures across the state, CalEPA found that "[t]he highest temperatures crop up east of downtown Los Angeles and are pushed into the inland valley by ocean breezes," writes Sanden Totten, science reporter for KPCC. [Listen here]

"In that way we found that the urban heat island effect in the L.A. area really mimicked the ozone pollution problem in L.A. where it moved east and settles against the hills," said Gina Solomon, Deputy Secretary for Science and Health with CalEPA.

She adds that the index, a result of 2012 legislation (AB 296, Chapter 667, Statutes of 2012), is a way of "quantifying the urban heat island effect." It "is designed so that cities can have a quantifiable goal for heat reduction," according to the webpage.

"We call it not an urban heat island but an urban heat archipelago because it's like a whole chain of urban heat islands that run into each other," Solomon said.

“The Urban Heat Island Index offers state and local governments a tool to help prioritize areas for programs that reduce heat in urban communities, such as urban greening projects and cooler roofs and pavements," notes the press release.

Monday, September 21, 2015 in KPCC

portrait of professional woman

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching. Mary G., Urban Planner

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching.

Mary G., Urban Planner

Get top-rated, practical training

High-rise apartment buildings in Waikiki, Hawaii with steep green mountains in background.

Study: Maui’s Plan to Convert Vacation Rentals to Long-Term Housing Could Cause Nearly $1 Billion Economic Loss

The plan would reduce visitor accommodation by 25,% resulting in 1,900 jobs lost.

April 6, 2025 - Honolulu Civil Beat

Two yellow and white Dallas Area Rapid Transit light rail streetcars at station in Dallas, Texas.

North Texas Transit Leaders Tout Benefits of TOD for Growing Region

At a summit focused on transit-oriented development, policymakers discussed how North Texas’ expanded light rail system can serve as a tool for economic growth.

April 3, 2025 - KERA News

Blue and white Seattle Link light rail train exiting concrete Downtown Bellevue Tunnel in Bellevue, WA.

Why Should We Subsidize Public Transportation?

Many public transit agencies face financial stress due to rising costs, declining fare revenue, and declining subsidies. Transit advocates must provide a strong business case for increasing public transit funding.

April 7, 2025 - Todd Litman

Amtrak Acela

How to Make US Trains Faster

Changes to boarding platforms and a switch to electric trains could improve U.S. passenger rail service without the added cost of high-speed rail.

2 hours ago - Bloomberg CityLab

Mural showing tools and craft supplies with banner reading 'Things are made here' in front of makerspace in Columbia, Missouri.

Columbia’s Revitalized ‘Loop’ Is a Hub for Local Entrepreneurs

A focus on small businesses is helping a commercial corridor in Columbia, Missouri thrive.

3 hours ago - Next City

Close-up of wood log with emerald ash borer larvae tracks etched in the wood.

Invasive Insect Threatens Minnesota’s Ash Forests

The Emerald Ash Borer is a rapidly spreading invasive pest threatening Minnesota’s ash trees, and homeowners are encouraged to plant diverse replacement species, avoid moving ash firewood, and monitor for signs of infestation.

4 hours ago - The Bemidji Pioneer