Climate scientists are warning that a 'super' El Niño, expected to be the strongest of the century, could bring a wet winter and increased flooding risk to the western and south-eastern United States. According to the US National Oceanic and Atmospheric Administration (Noaa), the weather system, characterized by above-average sea surface temperatures in the central and eastern equatorial Pacific, is predicted to intensify in the fall and winter, persisting until early spring 2027.
High Chances of Above-Average Rainfall in California
California's coast has a 70% to 100% chance of experiencing above-average rainfall, according to a model from the European Centre for Medium-Range Weather Forecasts. Daniel Swain, a UCLA climate scientist, noted at a virtual El Niño town hall hosted by California state senator Mike McGuire that while 'El Niño is never going to guarantee any particular outcome in any California winter,' a weather event as strong as predicted 'shifts the odds in favor of a wet winter.' He added that this 'will likely affect and increase the likelihood of coastal flooding, particularly during strong storm events or during king tide events.'
Historical Devastation from El Niño
California has faced severe impacts from past El Niños. The 1982-83 event destroyed 33 ocean-front homes and damaged 3,000 other residences, according to the California Coastal Commission. In 1997-98, massive flooding led to 17 storm-related deaths. More recently, the 2015-16 El Niño winter caused record coastal erosion on California beaches.
Mark Merrifield of the Scripps Institution of Oceanography warned at the town hall that '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.'
Drought Not Fully Relieved
Despite the expected rainfall, El Niño is not anticipated to completely erase drought in the US south-west, where some reservoirs are at all-time lows. 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 'it would have to be exceptionally wet,' which would also bring flooding, destruction, and potential loss of life.
Impacts on Gulf and East Coasts
Swathes of the US Gulf coast and east coast, from Florida to the mid-Atlantic region, face similarly 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 1998 El Niño winter, an outbreak of unusually strong tornadoes in that region led to 42 deaths and more than $100m in damage.
Variability and Future Climate Stress Test
Experts caution that not every El Niño behaves the same, nor does it affect different geographical regions uniformly. Some have fueled hurricanes and heavy precipitation, while others have triggered extreme heat and drought. Merrifield described the phenomenon as a 'natural cycle,' but noted that the temporary sea-level rise from the super El Niño 'gives us a bit of a stress test of what the state is likely to experience with future climate change.' He added, '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, and it also is a sobering look at what we can expect with climate change.'
