California’s coastline is bracing for a double hit this winter and six places, from San Luis Obispo to Humboldt Bay, are facing an enhanced flooding and erosion risk.

According to a new study released by UC Davis these key geographic hotspots are likely to witness a loss of beaches, shoreline property damage, bluff instability, and temporary or permanent infrastructure destruction.

According to the study, this extreme weather is driven by a foot of sea-level rise from climate change, alongside what could be the strongest El Niño on record. 

The six places facing biggest flooding risk are:

1. San Luis Obispo County: Public beaches and roadways in Avila Beach and Pismo Beach face severe erosion and wave damage.
2. Monterey & Santa Cruz Coastline: The Elkhorn Slough area, Moss Landing, local roads, agricultural fields, and shoreline housing in Santa Cruz are vulnerable to heavy inundation.
3. South San Francisco Bay: Residential areas, local roads, marshes, and major transportation hubs—including San Francisco International Airport, East Bay marshes, and the eastern approach of the Bay Bridge along I-80—face high flood risks.
4. Marin & North Bay Arterials: US-101 in Corte Madera, residential sectors in San Rafael, and critical segments of Highway 37 near Novato Creek, Petaluma River, and Mare Island are highly susceptible to saltwater flooding.
5. Stinson Beach: Frontline oceanfront homes, local roadways, and beach infrastructure are directly threatened by storm surge and coastal erosion.
6. Humboldt Bay: Surrounding agricultural fields, local roadways, US-101 corridors, and low-lying marshes face high vulnerability from compounding high tides and runoff.

“All the problems we are seeing now were predicted years ago and we should not be surprised when they start happening,” Fraser M. Shilling, Director Road Ecology Center, UC Davis, said in the study.

An eastern Pacific “Kelvin wave” paired with storm tracks that continually shove water inland has already exposed Southern California to powerful surf, high tides, and historic flooding, the study said. 

Researchers warn that the threat is far from theoretical. In the winter of 2019, atmospheric river storms pushed coastal waters up by nearly 10 inches, shutting down Highway 37 in the North Bay during an otherwise weak El Niño, the study noted. 

“It is possible that the beach flooding in Southern California is resulting in irreversible damage to the beaches of Long Beach and Newport Peninsula areas which even extensive riprap and sand augmentation won’t solve,” Shilling added.

Experts warn that stacking these elevated base sea levels with open-coast swells and inland runoff will trigger severe flooding and accelerated erosion statewide.

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