Coastal hazards along the U.S. West Coast during the 2015-16 El Niño

The variability of the El Nino-Southern Oscillation is the dominant driver of inter-annual coastal hazards risk across the Pacific Basin, with the Eastern North Pacific region typically subjected to elevated waves and water levels during the El Niño end member of that climate cycle. Based on climate indices stretching back 145 years, the 2015-16 El Niño was one of the three strongest events ever recorded, along with 1982-83 and 1997-98. By analyzing the last several decades of wave and water level data coupled with the behavior of 29 beaches scattered across the U.S. West Coast, we show that oceanographic forcing and coastal response was unprecedented for many locations during the winter of 2015-16. Winter beach erosion across the study area was 76% above normal, and most beaches in California eroded beyond historical extremes. However, damages across the region were mitigated by anomalously large beach sand volumes at the onset of the El Niño event, driven by unusually low-wave energy conditions in the preceding years, particularly in the Pacific Northwest. Nevertheless, if severe El Niño events become more common in the future as some studies suggest, this coastal region, home to over 25 million people, may become increasingly vulnerable to coastal hazards independent of projected sea level rise.