Kelvin Waves Could Amplify Coastal Flooding and Erosion Along West Coast

Sea levels along the West Coast are projected to rise by up to a foot this month as a series of warm water pulses, called Kelvin waves, make their way north along the shoreline. This phenomenon is raising concerns about increased beach erosion and flooding, particularly for areas already affected by climate change and El Niño.

Kelvin waves are not tsunamis, but rather bulges of water that lift sea levels as they travel. These waves are common during El Niño events, and experts suggest that the current strong El Niño could intensify their impact. The surge, measuring between 6 inches and a foot in height, will move north along the California coast at approximately 6 miles per hour, reaching Oregon and Washington state. These waves are expected to continue passing through from October until February.

"It’s not that this Kelvin wave is going to come and flood anything on its own," said Michael Jacox, a research oceanographer with the National Oceanic and Atmospheric Administration Fisheries’ Ecosystem Science Division. "Instead, it raises the baseline." This means that when high tides, storms, or storm surges occur, the water levels will be amplified by the elevated baseline, potentially leading to greater impacts.

In addition to raising sea levels, Kelvin waves can also increase ocean temperatures and push colder, nutrient-rich waters deeper, affecting marine life.

Kelvin waves form when trade winds along the equator change direction. Typically, winds blowing from east to west push Pacific Ocean water toward Asia. When these winds weaken or reverse, the accumulated water is pushed back east toward South America. Upon reaching the coast of South America, the surge then moves north and south along the coasts of North and South America. The waves themselves are not visible to the naked eye and extend approximately 12 to 20 miles offshore and about 200 meters deep.

Many coastal communities are already contending with rising sea levels and coastal erosion. The higher sea levels associated with Kelvin waves could worsen these existing problems. Experts note that higher sea levels combined with larger-than-average waves, expected from North Pacific swell during El Niño, and large spring tides from October to February, can lead to severe erosion on the West Coast. Major El Niño events in the past, such as those in 1982-83, 1997-98, and 2015-16, have historically caused record erosion along West Coast beaches. The loss of protective beaches can further increase the impact of waves and coastal flooding on property and infrastructure.

Experts anticipate that more Kelvin waves may arrive over the winter, potentially intensifying conditions. While El Niño events typically see five or six Kelvin waves, the current event is being closely monitored. One wave has already occurred, and evidence suggests a third is forming.

In Southern California, concerns are mounting about potential damage, especially given recent incidents where waves have threatened a seaside rail line and caused damage to oceanfront homes. Authorities are working to place emergency sand on beaches, anticipating that the Kelvin Wave could raise water levels significantly.

California Governor Gavin Newsom declared a state of emergency in late September to prepare the state for a potentially historic El Niño season, aiming to expedite protective measures for communities and resources. Officials in Washington state are also prepared to respond to any potential disasters associated with the Kelvin waves, coordinating with the state Emergency Management Division.

The full extent of damage will depend on the interplay of these Kelvin waves with storms and tides amplified by El Niño. While it is too early to definitively predict if this winter season will set new records, current indicators suggest this El Niño is on track to be one of the largest on record.