Sea levels along the US West Coast could rise by up to a foot, about 30 centimetres, this month as Kelvin waves move north, according to Associated Press and AFP reports published on October 3. Scientists warn that these warm-water pulses linked to El Niño could increase exposure to coastal flooding and beach erosion when they coincide with high tides and storms.
AP reported that the approaching pulse could raise water levels by roughly 15 to 30 centimetres, with effects extending from California toward Oregon and Washington. Experts interviewed by the agency expect further pulses between October and February. These figures describe an expected rise in sea level, rather than a measurement already recorded everywhere along the coast.
The phenomenon is different from a tsunami or a breaking surf wave. AFP describes a broad, sustained bulge of water travelling along the shoreline. In its background explanation, NOAA Fisheries says weakening or reversing equatorial winds generate waves that travel east across the Pacific before turning north along the American coast.
Dillon Amaya, a marine scientist at North Carolina State University, told AFP that the higher water level can magnify the effects of storm surges, large swells and exceptionally high tides. He also explained that warmer water expands, adding to the rise. The danger therefore depends on the combination of ocean and weather conditions, rather than on the pulse alone.
The environmental concerns extend below the surface. NOAA Fisheries explains that Kelvin waves deepen the boundary between warmer upper waters and colder water beneath. El Niño can also weaken the winds that normally bring cold, nutrient-rich water upward. Together, these processes warm coastal waters and alter the conditions supporting marine life.
NOAA's California Current assessment identifies prolonged warmth as a major risk to marine resources when El Niño follows existing marine heatwaves. The agency is monitoring the ecosystem with satellites, surveys and partner institutions, and is seeking unusual observations from fishing crews. That monitoring will help track how conditions develop as the autumn and winter pulses arrive.
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