LA area has highest urban heat island effect in California

One of downsides of living in a city is that heat can be absorbed in the concrete and pavement of buildings and streets, creating so-called urban heat islands.

To find out which areas of the state are most affected, the California Environmental Protection Agency created a first-of-its-kind index tracking temperatures across the state.

"We took the first try at quantifying the urban heat island," explained Gina Solomon, Deputy Secretary for Science and Health with CalEPA.

Her team found that the greater L.A. area sees more additional heat than any other region, in part because of how urbanized it is.

"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.

Urban heat island temperatures in the greater Los Angeles area. Image via CalEPA.

The researchers used temperature records and atmospheric models to assess the temperature of various cities across California. They then compared those temperatures with nearby rural areas that see similar heat.

By noting how much hotter cities were, CalEPA was able to see how much additional heat was trapped by pavement and concrete.

During the summer in some parts of the L.A. region, temperatures could jump 19 degrees Fahrenheit due to this effect.

The highest temperatures crop up east of downtown Los Angeles and are pushed into the inland valley by ocean breezes. The heat then pools in the foothills of the San Bernardino Mountains.

"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," Solomon said.

Some regions, like Bakersfield, are prone to high summer temperatures, but the researchers found this didn't always lead to extreme heat islands, since that city is not as urbanized as other places.

Urban heat island temperatures in Bakersfield. Image via CalEPA.

Solomon says pinpointing the areas most affected by urban heat is important since there’s a lot that can be done to cool things down.

Solutions include planting more trees and bushes, painting roofs white so they don’t absorb as much heat and using lighter colored concrete on streets and sidewalks.

She added that it's also important to warn the young, elderly and other vulnerable populations in those areas so they can take extra precautions when extreme heat is expected.