An analysis by NASA's Sea Level Change Science Team found that if a strong El Niño occurs this winter, cities along the West Coast of the Americas may experience an increased frequency of high-tide flooding that can swamp roads and spread into lower-lying buildings.
In January 2023, an unusually large tide known as the "King Tide" flooded a highway ramp in Northern California. Rising sea levels and El Niño can exacerbate such flooding. The kind of high-tide flooding that inundates roads and buildings on the West Coast of the Americas tends to be uncommon outside of El Niño years, but that could change by the 2030s. Source: California King Tide Project
El Niño is a cyclical climate phenomenon characterized by higher than normal sea levels and above-average ocean temperatures along the equatorial Pacific coast. These conditions will spread poleward along the western coast of America. This year's still-developing El Niño will bring more rain than usual to the southwestern United States and drought to countries in the western Pacific, such as Indonesia. These effects usually occur from January to March.
Flood event prediction
A NASA analysis has found that a strong El Niño could cause up to five so-called once-in-10-year flooding events in cities such as Seattle and San Diego this winter. Places like La Libertad and Baltra in Ecuador could see up to three 10-year floods this winter. This type of flooding does not typically occur on the west coast of the Americas outside of El Niño years. The researchers noted that by the 2030s, rising sea levels and climate change could cause these cities to experience a similar number of once-in-a-decade floods each year, without the need for El Niño.
Data from the SWOT satellite shows sea level anomalies - how much sea levels have risen or fallen compared to the average height - on August 12, 2023, and October 3, 2023, along the coasts of Ecuador and Peru. These data indicate that an El Niño is developing along the west coast of the Americas. Source: NASA/JPL-Caltech
"I'm a little surprised how quickly these once-in-a-decade events can become commonplace," said Phil Thompson, an oceanographer at the University of Hawaii and a member of NASA's sea-level change science team. "I thought maybe by the 1940s or 1950s that would be the case."
A 10-year flood is one that has a 1 in 10 chance of occurring in any given year. They are a measure of how high local sea levels are: the extent of flooding in a particular city or neighborhood depends on several factors, including the topography of the area and the location of homes and infrastructure relative to the ocean. The once-in-a-decade flood could result in what the National Oceanic and Atmospheric Administration classifies as moderate flooding, inundating some roads and buildings and possibly requiring evacuations or moving belongings to higher ground.
NASA's coastal flooding analysis found that by the 2030s, cities on the West Coast of the Americas could experience up to 10 of these once-in-a-decade floods during strong El Niño years. By the 2050s, strong El Niño could cause up to 40 such events a year.
Watch sea level rise
Water expands as it warms, so sea levels tend to be higher where the water is warmer. Researchers and forecasters monitor ocean temperatures and water levels to spot the formation and development of El Niño.
"Climate change is already changing baseline sea levels along coastlines around the world," said Ben Hamlington, a sea level researcher at NASA's Jet Propulsion Laboratory in Southern California and leader of the agency's sea level change science team.
Sea levels are rising as the Earth warms as the Earth's atmosphere and oceans heat up and ice sheets and ice shelves melt. This has increased the number of days throughout the year that coastal cities experience high tides or flooding. Phenomenons such as El Niño and storm surges can temporarily raise sea levels, exacerbating these effects.
Missions that monitor sea level, including the Surface Water and Ocean Topography (SWOT) satellite and Michael Freilich Sentinel-6, help monitor El Niño in the short term. SWOT, in particular, collects sea level data right down to the coast, helping to improve predictions of sea level rise. This information can help policymakers and planners prepare communities for rising sea levels in the coming decades.
"As climate change accelerates, the frequency of flooding in some cities will increase by 5 to 10 times," said Nadya Vinogradova Shiffer, a SWOT project scientist and director of the Ocean Physics Program at NASA Headquarters in Washington. "SWOT will pay close attention to these changes to ensure that coastal communities are not caught off guard."