San Francisco named top 'urban heat island' in new climate report, but what does this mean?

ByTim Didion and Drew Tuma KGO logo
Wednesday, August 18, 2021
SF is a 'heat island' and it could be making temps hotter, report says
Watching the cool grey fog roll in, it may stretch your imagination to consider San Francisco a heat island, but not when you consider the criteria.

SAN FRANCISCO (KGO) -- Watching the cool grey fog roll in, it may stretch your imagination to consider San Francisco a heat island, but not when you consider the criteria.

"Basically, all we're saying is if the landscape and geography wasn't as it was, you guys would be even colder," explained senior data analyst Jennifer Brady of the nonprofit news organization Climate Central.

Brady and her colleague Kaitlyn Weber broke down the criteria that helped place San Francisco no. 5 on a list of the top 20 Urban Heat Islands nationwide in a recent Climate Central report. They say the index ranks the heat patterns in a city against its natural outlying area, focusing on the man made factors that heat it up.

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"What things we build our buildings with, the height mixture, the variety of the heights and stuff like that," said Weber.

The report points to factors like high-rise canyons that trap hot air, building and road materials that absorb heat rather than reflect it and a scarcity of natural environmental coolers like tree canopy. They say that can all add up to a seven degree increase in average temperature during summer months.

The forces that come together to create urban heat islands can be complicated, but luckily there are things that city's can do to help cool things down a little.

Robin Grossinger is with the San Francisco Estuary Institute. The group is working with the city as part of a large scale planning project called Next Generation Urban Greening.

"To help them figure out how to maximize urban greening, tree canopy the kind of things that we were talking about, tree canopy storm water infrastructure," explained Grossinger.

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At a full five feet, cyclical flooding coupled with other impacts of climate change could begin to cause havoc in the Bay Area.

San Francisco has already introduced programs to green streets that allow storm water to penetrate sidewalks. Grossinger says the challenge in many cities is to expand the greening into denser and sometimes lower income neighborhoods, where the buildings and sidewalks weren't laid out to accommodate trees.

"It is a challenge with the affordability and housing crisis, because obviously we need to make our cities denser, but we think we also need to make them greener at the same time," he said.

Proposed solutions include reconfiguring sidewalks to make room for trees, adding roof gardens and using more heat reflective materials in buildings roads. It's a challenge that will take planning, perhaps block by block.

"If you have a neighborhood that has a problem and it's probably hotter than another neighborhood, you can think about what are some of the small changes we can make to bring the temperatures down," Brady said.

"And since we know the climate is changing, and we know we expect it to continue to be changing, we can use these things to better build in the future," added Weber.

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According to Climate Central, several desert cities in the southwest did not make the list. That's because even though they're warm because of natural heat, they're building materials and layouts actually take advantage of the cooling opportunities available.

Editors Note: This story was produced as a collaboration between ABC7 News and Climate Central as members of the Local Media Association's climate collaborative, a network of participating media outlets working together to improve coverage of climate issues.