Kelvin wave could raise California sea levels by up to a foot for months

Newsom declares state of emergency ahead of forecasted storms and coastal flooding

A planetary-scale ocean phenomenon known as a kelvin wave is approaching California’s coastline and could raise sea levels by up to a foot for months, according to scientists studying ocean circulation at NASA’s Jet Propulsion Laboratory and NOAA’s Southwest Fisheries Science Center. The wave reached the northern tip of South America in late August and has begun moving toward the west coast of the US, scientists said. California Governor Gavin Newsom declared a state of emergency this week ahead of forecast winter storms, storm surges and coastal flooding.

Sea levels along the California coast have already risen about 8 inches over the past century, and researchers said the combined effect of the kelvin wave and an exceptionally strong El Niño could exceed damage from previous major El Niño winters. The El Niño climate pattern has already surged past its highest recorded temperature several months before its expected peak.

In a typical year, a thick layer of warm water sits in the western Pacific, held in place by trade winds that usually blow from South America toward Asia. The kelvin wave phenomenon forms when those winds die down or reverse during El Niño years, releasing the warm water as a slow-moving slosh that spans thousands of miles, carrying it across the Pacific along the equator toward South, Central and North America.

“You can follow them along. We see the higher sea levels along the equator, and when the wave reaches the coast of South America, it cannot continue to go eastward,” said Severine Fournier, a research scientist at NASA’s Jet Propulsion Laboratory. “So it goes north and south.”

Nate Mantua, a research scientist at NOAA’s Southwest Fisheries Science Center, explained the slosh mechanism: “When the wind stops blowing or weakens, the force that’s holding that pile of water in place goes away, so that water surges or sloshes back towards California.” Researchers expect the influence of the kelvin wave to linger through the winter and into early next year, Mantua said.

Kelvin waves are a natural phenomenon that have been happening for thousands of years and measured by agencies like NOAA since record-keeping began, Mantua said. Sea levels along the California coast have already risen about 8 inches over the past century, meaning the kelvin wave will add water on top of a figure that’s already going up, he said. “We can predict a lot of the impacts,” he added, “but not all.”

The current wave reached the northern tip of South America in late August and could arrive at California within days, scientists said. Once it reaches the coast, it could elevate sea levels for months as the ongoing El Niño keeps the warm water trapped against the shore.

This year’s El Niño is likely to be the largest in at least 1,000 years, and climate readings have already surged past the highest temperature ever recorded for the phenomenon several months before its expected peak. The climate pattern brings increased risk of severe storms, storm surges, flooding and coastal erosion.

“It’s a wave unlike the ones you’re used to at the beach. They don’t crash, you can’t really seem them come by,” said Mike Jacox, a research oceanographer at NOAA’s Southwest Fisheries Science Center. “This winter, we’re supposed to have some really high tides around Thanksgiving and Christmas. If you also have more storms, then you have storm surge. It’s just like you’re raising the floor on all that stuff that happens.”

California is preparing for a potentially severe season. Governor Gavin Newsom declared a state of emergency this week, mobilizing state resources ahead of potential winter storms, coastal flooding and other impacts. Road-closure and snow-removal equipment is being staged along highways; the state national guard is being prepared for search-and-rescue operations; and agencies are identifying ways to cut red tape in the event of a natural disaster.

The California Coastal Commission, which plans and regulates the use of land and water along the state’s coastline, has urged homeowners and residents to prepare by inspecting areas vulnerable to flooding or erosion, adding drainage and addressing causes of damage before severe weather arrives. “A key observation from past El Niño events is that the most damaging storms are often those that coincide with the highest tides,” wrote Kate Huckelbridge, the commission’s head, in a memo earlier this month. “Storms that peak during high tides are far more likely to cause damage than if the same storm peaked during low tide.”

Past strong El Niño years — 1983, 1998 and 2016 — have helped researchers refine predictions of where and how damage can occur, Mantua said. But with rising baseline sea levels and what he called the “really exceptional intensity of this event,” Mantua warned the season “may end up causing even more damage than we’ve seen in major El Niño winters.”

“In the El Niño winters in the northern Pacific, we tend to have a lot of storminess, we tend to have more storms and big storm waves in the ocean than we typically do,” Mantua said. “So you add that on top of this elevated sea level… then you just expose places to more of the ocean’s energy and simple inundation.”