An exceptionally energetic hurricane season, fuelled by unusually warm ocean waters and a powerful El Niño, has caused extensive coastal damage in Southern California, raising concerns about erosion and flooding this winter.
The Pacific Ocean has experienced record levels of accumulated cyclone energy this summer, surpassing the previous seasonal high set in 2018, researchers at Colorado State University confirmed. The measure accounts for the intensity, duration and wind energy of tropical storms and hurricanes.
The impact is already visible along Southern California’s coastline, where powerful waves have damaged infrastructure, threatened beachfront homes and stripped sand from beaches before the region’s winter storms have even begun.
“It’s been a wild season,” said Daniel Cayan, a climate researcher at the Scripps Institution of Oceanography at the University of California, San Diego.
In Long Beach, repeated storms caused sections of the historic boardwalk to buckle. As Tropical Storm Rachel approached over the weekend, large waves battered oceanfront properties, leaving some homes at risk of collapse.
In Newport Beach, a swell roughly twice as large as initially forecast overwhelmed 20-foot beach berms, sending seawater onto roads. Other areas, including the Wedge in Newport Beach, San Onofre, Laguna Beach and San Clemente, have also experienced substantial changes as waves and elevated sea levels washed away sand.
The damage prompted Orange County to declare an emergency last month.
Warm waters and El Niño fuel storm activity
Scientists attribute the unusually active season to a combination of long-term ocean warming associated with climate change and the effects of El Niño.
According to Daniel Swain, a climate scientist with UC Agriculture and Natural Resources, El Niño can create conditions that favour tropical cyclones by raising ocean temperatures and reducing wind shear, which can otherwise weaken storms.
“ So it adds more fuel and it makes that fuel more likely to take advantage of its environment,” Swain said during a recent webinar.
Tropical storms normally weaken as they move over the cooler waters of the eastern Pacific. This year, however, a marine heatwave and El Niño conditions have pushed ocean temperatures 10 to 13 degrees above normal in some areas, helping storms retain their strength as they approach the California coast.
The combination of powerful waves, high tides and a Kelvin wave — an ocean disturbance that can raise background sea levels by 6 to 12 inches — has intensified coastal impacts.
Further storm activity remains possible. Hurricane Simon, which is moving along Mexico’s western coast, is expected to make landfall there, while forecasters have estimated a roughly 90% chance of another cyclone forming within seven days.
“I wouldn’t be surprised if we saw a couple more hurricanes or tropical systems forming in the Central Pacific, South Pacific area,” said Kristan Lund, a meteorologist with the National Weather Service in Oxnard.
Winter brings fresh risks
Southern California is now preparing for what could be an unusually severe winter. The US National Oceanic and Atmospheric Administration’s Climate Prediction Center said last week that there was virtually a 100% probability of a “very strong” El Niño this season. The likelihood that it will be the strongest on record since 1950 rose to 83%, from 75% the previous month.
Even without exceptionally heavy rainfall, El Niño can intensify coastal erosion. Beaches generally lose sand during winter, when powerful waves carry it offshore, and regain some of it during calmer summer conditions. Stronger-than-normal winter waves can disrupt that cycle, accelerating erosion and increasing the risk of damage to coastal infrastructure.
“There’s likely to be pretty profound influences along the coast,” Cayan said, warning that powerful waves can also trigger cliff failures and other damage.
Previous strong El Niño events offer a warning. The winters of 1982–83 and 1997–98 brought extensive damage to Southern California, including flooding, damaged piers and threatened homes. The 2015–16 event, meanwhile, caused record coastal erosion despite rainfall that was not above average.
Researchers found that waves during the 2015–16 winter were about 50% larger than usual, while beach erosion was 76% higher than normal.
Cayan said California had avoided some of the worst consequences of recent winter storms because they did not coincide with the highest tides. This year, the timing could prove critical.
King tides, which can push water levels above 7 feet and potentially higher during El Niño, are expected around Thanksgiving, Christmas and late January.
If powerful storms coincide with those periods, the coastline could face substantial erosion, flooding and damage to roads, homes and other infrastructure.
“Those periods are really critical for the fate of the California coastline and infrastructure this winter,” Cayan said.
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