California’s coastline is preparing for a potentially damaging double threat this winter, with six areas stretching from San Luis Obispo to Humboldt Bay facing heightened risks of flooding and erosion.
A new study from UC Davis identifies these geographic hotspots as particularly vulnerable to beach loss, property damage, unstable coastal bluffs, and the temporary or permanent destruction of infrastructure.
The study attributes the threat to roughly a foot of climate-driven sea-level rise combined with what could become the strongest El Niño on record.
The six areas facing the greatest flood and erosion risks are:
- San Luis Obispo County: Public beaches and roads in Avila Beach and Pismo Beach could face severe erosion and damage from powerful waves.
- Monterey & Santa Cruz Coastline: The Elkhorn Slough region, Moss Landing, nearby roads, agricultural land, and coastal homes in Santa Cruz are vulnerable to extensive inundation.
- South San Francisco Bay: Homes, local roads, marshlands, and major transportation centers—including San Francisco International Airport, East Bay marshes, and the eastern approach to the Bay Bridge along I-80—face significant flooding threats.
- Marin & North Bay Arterials: US-101 in Corte Madera, residential neighborhoods in San Rafael, and key sections of Highway 37 near Novato Creek, the Petaluma River, and Mare Island are highly exposed to saltwater flooding.
- Stinson Beach: Oceanfront homes, local roads, and beach facilities are directly at risk from storm surge and coastal erosion.
- Humboldt Bay: Nearby farmland, local roads, US-101 corridors, and low-lying marshes face serious threats from the combined effects of 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 of the Road Ecology Center at UC Davis, said in the study.
The study said an eastern Pacific “Kelvin wave,” combined with storm systems that repeatedly push water inland, has already exposed Southern California to powerful surf, elevated tides, and historic flooding.
Researchers caution that the danger is not merely theoretical. During the winter of 2019, atmospheric river storms raised coastal water levels by nearly 10 inches and closed Highway 37 in the North Bay, despite the presence of a relatively weak El Niño, according to the study.
“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 higher baseline sea levels, open-coast swells, and runoff from inland areas could combine to produce severe flooding and accelerate erosion along California’s coast.
