SEATTLE (AP) — Sea levels along the West Coast are projected to rise by up to a foot this month due to a series of warm water pulses known as Kelvin waves, which are raising concerns about beach erosion and flooding in areas already affected by climate change and El Niño. Kelvin waves are characterized by water bulges that elevate sea levels as they travel along the coast, and they are commonly associated with El Niño events. Experts suggest that this year's super El Niño may amplify these effects.
The surge, measuring between 6 inches to a foot, is expected to move north along the California coast at approximately 6 miles per hour (9.6 kilometers per hour), reaching Oregon and Washington state. The waves are anticipated to continue passing through from October until February.
Michael Jacox, a research oceanographer with the National Oceanic and Atmospheric Administration Fisheries' Ecosystem Science Division, stated, "It's not that this Kelvin wave is going to come and flood anything on its own." He explained that elevated sea levels can exacerbate flooding during high tides, storms, or storm surges.
The Kelvin waves also contribute to increased ocean temperatures and push cold, nutrient-rich waters deeper, affecting marine life. Dillon Amaya, an assistant professor at North Carolina State University, noted that Kelvin waves are a regular occurrence during El Niño, which involves warming ocean waters. These waves form when trade winds along the equator shift direction, causing water to move back toward the east along the equator until it reaches the coast of South America.
The waves are not visible and do not cause noticeable changes in boat movement; they are described as a broad bulge extending 12 to 20 miles (19 to 32 kilometers) offshore and about 200 meters deep. Coastal communities are already facing challenges from rising sea levels, such as erosion in San Clemente, California, where waves are increasing in size.
Sean Vitousek, a research oceanographer with the U.S. Geological Survey, indicated that the combination of higher sea levels, larger waves from North Pacific swells, and significant spring tides could lead to exceptional erosion along the West Coast. Historical data shows that major El Niño events in 1982-83, 1997-98, and 2015-16 resulted in severe beach erosion.
Alyssa Napuri, deputy chief of staff for Orange County Supervisor Katrina Foley, expressed concern that the Kelvin waves could worsen existing issues along the Southern California coast. Emergency sand is being placed on beaches in anticipation of the waves, which could raise water levels by 6 to 12 inches.
California Governor Gavin Newsom declared a state of emergency in late September to prepare for what is expected to be a significant El Niño season, allowing for faster resource mobilization and community protection. Experts from the Washington state Department of Natural Resources are also preparing for potential impacts from the Kelvin waves, although no special preparations have been requested so far.
The extent of damage from the Kelvin waves will depend on the strength of storms and tides influenced by El Niño. Amaya noted that while it is too early to determine if this winter season will set records for El Niño activity, it is on track to be one of the largest events recorded. Associated Press reporter Amy Taxin contributed to this story from Santa Ana, California.