A Pulse of Warm Water Hitting the Pacific Coast Could Mean Erosion and Flooding

Sea levels along the West Coast are expected to rise by up to one foot this month because of powerful waves of warm water called Kelvin waves. These waves are moving north along the shoreline and could cause beach erosion and flooding. Scientists are especially worried because the coast is already dealing with the effects of climate change and a strong El Niño weather pattern this year. Communities from California to Washington state are now preparing for the worst.

Kelvin waves are nothing like tsunamis. They don't curl up and crash onto the beach. A better way to picture them is water sloshing back and forth in a bathtub during an earthquake. In the ocean, they are bulges of water that slowly raise sea levels as they travel along the coast. They are common during El Niño events, but experts say this year's extra-strong El Niño could make their effects much more serious.

Over the next week, a surge of water six inches to one foot tall will move north along the California coast at about six miles per hour, or 150 miles per day. That means higher sea levels will soon reach Oregon and Washington state as well. Scientists predict these waves will keep arriving from October through February. One wave already passed through in May or June, and a third one is now forming.

Michael Jacox is a research oceanographer with the National Oceanic and Atmospheric Administration. He explained that a Kelvin wave alone won't flood towns. Instead, it raises the starting point for water levels. So when a big storm or high tide hits, the water is already six inches higher than usual — and the damage can be much worse. 'The effects can be amplified,' he said.

Kelvin waves form when trade winds near the equator slow down or change direction. Normally, those winds push warm Pacific Ocean water westward toward Asia. When the winds weaken or reverse, that bulge of water gets pushed back east until it hits South America. From there, it travels north and south along the coasts of North and South America. The wave can't be seen with the naked eye and won't make boats rock up and down — it's more like a giant flat pancake stretching 12 to 20 miles out from shore.

Many coastal communities are already struggling with rising sea levels. For example, the beach in San Clemente, California is being slowly eaten away by erosion. Experts say waves are also getting bigger, and the Kelvin waves could make all of these problems worse. 'People are on edge,' said Dillon Amaya, a professor at North Carolina State University. 'They think about more flooding happening, more beach erosion.'

The combination of higher sea levels, bigger waves from the North Pacific, and large spring tides from October to February could cause serious erosion on the West Coast. Sean Vitousek, a researcher with the U.S. Geological Survey, noted that the biggest El Niño events in 1982–83, 1997–98, and 2015–16 caused the worst beach erosion on record. Losing beaches also means less protection for homes and other buildings near the water. 'The loss of protective beaches also increases wave impacts and coastal flooding on property and infrastructure,' Vitousek said.

Officials in Southern California are already taking action. Authorities are placing emergency sand on beaches as fast as they can to help protect the shoreline. Alyssa Napuri, a local official in Orange County, said water levels could rise six to twelve inches because of the Kelvin wave. Homes along the ocean were already damaged last month during swells tied to Hurricane Marie. 'We're already struggling as it is,' Napuri said.

California Governor Gavin Newsom declared a state of emergency in late September to help the state get ready for what could be a historic El Niño season. This declaration allows the state to act more quickly to protect communities, gather important resources, and get ready before the worst storms arrive. In Washington state, officials said they are ready to respond to any disasters, though they have not yet been asked to make special preparations.

How bad things get will depend on the strength of the storms and tides that come with El Niño. If the storms are stronger than usual, the damage could be very significant. Amaya said it is still too early to know for sure whether this winter will break records. However, he noted that this El Niño is already on track to be one of the biggest ever seen. 'This El Niño itself is certainly on that trajectory of being one of the largest if not the largest El Niño we've ever seen,' he said.