Severe Coastal Flooding in California Highlights El Niño Challenges

Homes and roads from Newport Beach to Long Beach have been damaged by this week’s coastal flooding. This event stems from a rare combination of factors, showcasing the challenges California might face with a predicted “super” El Niño winter. The flooding incidents are a stark reminder of how Tropical Storm Rachel, along with high tides, a record-hot ocean, and El Niño-generated waves, can impact coastal areas.

Unprecedented Events

Jonathan Warrick, a research geologist with the U.S. Geological Survey, highlighted how the combination of high tides, Kelvin waves, and hurricane-induced waves marks an unprecedented situation. With the possibility of a prolonged El Niño season, Californians could face a string of winter storms and king tides during the holiday season.

The center of Rachel was expected to move onshore in northern Baja California on Saturday night. Sunday morning presented the highest flooding risks for the Orange County and San Diego coasts. Swells, onshore winds, and high tides compounded these risks. High tide took place at 9:43 a.m. in La Jolla and 9:48 a.m. in Newport Beach.

Future Projections

According to Warrick and others, this week’s events might provide insights into future seasons. Although it is not certain we will experience similar conditions this winter, the trend indicates rising instances of such events with continued sea level rise.

The highest high tides typically occur around the summer and winter solstices. Notable instances are anticipated on Thanksgiving Day, Christmas Eve, and January 22. If these coincide with winter storms, they might lead to coastal erosion, flooding, and damage, as noted by Reinhard Flick, a researcher at the UC San Diego Scripps Institution of Oceanography.

Mark Merrifield, director of the Scripps’ Center for Climate Change Impacts and Adaptation, explained that large tides occur about every 18.6 and 4.4 years. California is currently nearing the peak of these cycles, which may lead to significant king tides around Christmas, boosted by high sea levels resulting from El Niño.

Historical Context

El Niño is a climate pattern characterized by unusually warm temperatures in the central and eastern equatorial Pacific Ocean, typically causing above-average precipitation in Southern California. Two of the strongest El Niños in recent decades resulted in substantial damage to the Southern California coast.

Another example, although it didn’t lead to excessive rainfall, caused record coastal erosion. During this week’s flooding in Orange County, Tropical Storm Rachel was a significant factor. The storm, downgraded from a hurricane, worked alongside an El Niño-driven Kelvin wave, which raised the background sea level by 6 to 12 inches.

The Kelvin wave could sustain elevated sea levels for an extended period. Dillon Amaya, a Kelvin wave expert and assistant professor at North Carolina State University, is monitoring another incoming Kelvin wave from Mexico, expected to affect Southern California in the coming weeks.

Reactive Measures

As the current Kelvin wave has already moved past Los Angeles and San Francisco, city officials are taking precautions. Sand berms and sandbags are being used to protect vulnerable areas from potential flooding.

The Los Angeles Harbor reported a tidal peak of 7.7 feet, higher than the predicted tide, and Sunday’s projected high tides were anticipated to challenge recent records for the county. Historically, only two storms had crossed near California at tropical storm strength, in 1939 and 1997, causing significant flooding and damage.

This year’s El Niño season is projected to be categorized as “very strong,” with the National Oceanic and Atmospheric Administration predicting an 83% chance it will break previous records.