Busy California airports used by millions of travelers could face flooding risks during the upcoming holiday season thanks to sea level rise and a record-breaking El Niño climate pattern, a new report warns.

While recent levee improvements have reduced the risk at Oakland International Airport, San Francisco International Airport – built on marshland – is vulnerable to flooding of 3 feet or more. That could ground flights, with takeoffs not recommended when standing water on the runway exceeds 0.5 inches.

“It doesn’t mean it’s certainly going to happen because it’s all about timing,” Fraser Shilling, director of the University of California-Davis Road Ecology Center, told KGO on Wednesday.

But with this week’s record tides seen up and down the California coast, experts fear much worse flooding is on the way.

“This was just like a preview. This is a trailer,” Shilling said.

There are flood protection measures in place at San Francisco’s airport, which had more than 1.8 million travelers just last Thanksgiving. Those measures include vinyl sheet pile walls, concrete seawalls and concrete-capped earthen berms, Doug Yakel, a public information officer at the airport, told The Independent.

“SFO facilities staff are also making preparations to reduce flooding risk which includes clearing drainage areas, ensuring pump stations are in top condition, clearing trees that could cause power outages, and preparing sand bags,” he said.

But Shilling told KGO that it was “clear from their description that none of those things are long-term protection.” Yakel did not address that comment.

The big picture

Climate change threats to infrastructure are accelerating, especially along U.S. coasts. This past week has been a prime example, with high tides breaking records in the Bay Area and in Southern California.

San Francisco blew past its previous October high tide records at 2.01 feet on Wednesday, according to Anthony Edwards, a meteorologist at the San Francisco Chronicle. Both San Diego and Los Angeles recorded their highest coastal water levels in over a century earlier this week.

The water has stranded drivers, submerged backyards and forced residents to travel by kayak and paddleboard.

The swelling tides – not yet king tides, per the state’s government – are fueled by near record high ocean temperatures offshore, El Niño-spurred pulses of energy known as Kelvin waves and the position of the moon.

Combining the effects of sea level rise, high tides, climate-related marine heat and the El Niño-driven Kelvin waves – which push water toward the coast – leads to a tidal height that’s at least 34 feet above normal, climate scientist Marc Alessi wrote this week in The Equation.

Recent models suggest that between 24 to 75 percent of California beaches could disappear seasonally or permanently by 2100 without taking action to make areas resilient to these effects.

With an upcoming peak in tides during the holiday travel season, December tides could be 1 to 2 feet higher than this week, according to Dr. Jeff Masters, an extreme weather and climate change expert.

Peak El Niño intensity is expected around November and December, climate scientist Daniel Swain noted in a post on his site Weather West. That means already hot, expanding seawater could continue to encroach farther on coastlines.

“Between November 2026 and January 2027, I would anticipate multiple significant coastal flood events that are worse in severity and also much more widespread than what we are currently seeing,” he wrote.