West Coast Braces for Rising Seas From Kelvin Waves
At a Glance
- A series of Kelvin waves is expected to raise sea levels along the U.S. West Coast.
- The higher water levels could increase coastal erosion and flooding risks during storms and high tides.
- The waves are linked to El Nino and are expected to continue through the winter.
- Authorities in California and Washington are monitoring conditions and preparing for possible impacts.
A series of warm-water pulses moving north along the U.S. West Coast is raising concerns over higher sea levels, coastal erosion, and flooding as El Nino intensifies.
Key Statements and Focus Area
- Coastal Risk: "The effects can be amplified"—Michael Jacox, NOAA Fisheries research oceanographer.
- Erosion and Flooding: "The loss of protective beaches also increases wave impacts and coastal flooding on property and infrastructure." — Sean Vitousek, U.S. Geological Survey research oceanographer.
- Focus Area: The main concern is how elevated sea levels could combine with storms, high tides, and larger waves to increase coastal hazards.
The Kelvin waves are expected to move north along the California coast at roughly 6 miles per hour, reaching Oregon and Washington as they travel along the shoreline. The elevated water levels are expected to range from about 6 inches to 1 foot.
Unlike a tsunami, a Kelvin wave does not produce a visible wall of water. It is a broad underwater bulge that raises sea levels as it travels along the coast.
Researchers say the waves develop during El Niño when changes in equatorial trade winds push warm water eastward across the Pacific. Once the water reaches the Americas, the resulting surge can move north and south along the coast.
The waves can extend roughly 12 to 20 miles offshore and reach about 200 meters in depth. They also raise ocean temperatures and push colder, nutrient-rich water deeper, potentially affecting marine ecosystems.
The immediate concern for coastal communities is the interaction between elevated sea levels and other conditions. High tides, storms, and larger North Pacific swells could produce significantly higher water levels than the Kelvin waves would create by themselves.
Researchers say the combination could be particularly challenging from October through February, when larger spring tides are expected. Previous major El Niño events, including those of 1982-83, 1997-98, and 2015-16, were associated with severe West Coast beach erosion.
The loss of beach material can also leave coastal infrastructure more exposed to waves and flooding. Southern California is already dealing with erosion, with waves approaching a seaside rail line and damage reported to oceanfront homes during recent swells.
Officials in the region are placing emergency sand on beaches in response to the coastal threat. California has also declared a state of emergency ahead of what authorities expect could be a major El Niño season.
Washington state officials are monitoring the situation and coordinating through the state's emergency management system, although no additional special preparations had been requested at the time of the report.
Researchers expect several Kelvin waves during a major El Niño. One wave passed through earlier in the year, while evidence indicates another is forming and could continue moving north during the coming weeks.
The extent of actual damage will depend largely on the strength and timing of storms, tides, and ocean swells during the winter.
FYI
Kelvin waves are a recurring feature of El Nino events and are driven by changes in Pacific Ocean circulation rather than by seismic activity. Their significance for coastal communities comes from their ability to temporarily raise the starting level of the sea.
El Niño itself is a naturally occurring climate pattern involving unusually warm ocean temperatures in the central and eastern tropical Pacific. Climate change is adding to longer-term sea-level rise, meaning temporary increases from ocean conditions can occur on top of an already elevated baseline.
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