El Niño, a recurring climate phenomenon marked by above-average sea surface temperatures, when changes in wind patterns allow warmer water to spread across the central and eastern equatorial Pacific, could spell a wet winter for portions of the western and south-eastern US, climate models show. Coastal areas may be at elevated risk of flooding, experts warn.
Climate scientists predict this year’s “super” El Niño, a label assigned when sea surface temperatures climb by at least ۲C, will be the strongest of the century. The weather system is expected to intensify in the fall and winter, persisting until early spring ۲۰۲۷, according to the US National Oceanic and Atmospheric Administration (Noaa).
California has a ۷۰%-۱۰۰% chance of experiencing above-average rainfall along its coast, according to a model from the European center for medium-range forecasts.
“El Niño is never going to guarantee any particular outcome in any California winter,” Daniel Swain, the UCLA climate scientist, noted at a virtual El Niño town hall hosted by California state senator Mike McGuire this week. But, he added, a weather event as strong as the one being currently predicted shifts the odds in favor of a wet winter: “That will likely affect and increase the likelihood of coastal flooding, particularly during strong storm events or during king tide events.”
California has been devastated by El Niños in the past.
A ۱۹۸۲-۸۳ weather system destroyed ۳۳ ocean-front homes and damaged ۳,۰۰۰ other residences, according to the California coastal commission. In a ۱۹۹۷-۹۸ El Niño, California experienced massive flooding and ۱۷ storm-related deaths. In more recent history, during the El Niño winter of ۲۰۱۵-۱۶, state officials reported record coastal erosion on California beaches.
“With less beach in front of the coastline, the waves will have even greater impact on the shoreline with more likelihood of flooding and undercutting of cliffs,” said Mark Merrifield of the Scripps Institution of Oceanography, at McGuire’s town hall.
El Niño is not expected to completely erase drought in the US south-west, where some reservoirs are at an all-time low. “It would have to be exceptionally wet,” Dr Joel Lisonbee, senior associate scientist at the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder, told the Guardian in June. “That would also mean flooding, and the destruction and potential loss of life that comes along with that.”
Swathes of the US Gulf coast and east coast, stretching from Florida up to the mid-Atlantic region, are facing similar high odds of increased precipitation.
During El Niño years, central and south Florida have historically experienced more severe weather with more tornadoes and flood events, according to Noaa. In a ۱۹۹۸ El Niño winter, an outbreak of unusually strong tornadoes in that region led to ۴۲ deaths and more than $۱۰۰m in damage.
Experts warn that not every El Niño behaves the same, nor does it affect different geographical regions in the same way. Some have fueled hurricanes and heavy precipitation, while others have triggered extreme heat and drought.
While this is “a natural cycle”, Merrifield said at the town hall, the potential effects of a temporary sea-level rise in California from the super El Niño also “gives us a bit of a stress test of what the state is likely to experience with future climate change”.
“The El Niño, I think, is a good opportunity to sort of see where our vulnerabilities are throughout the state and what we can do to prepare,” Merrifield added, “and it also is a sobering look at what we can expect with climate change.”
