It’s normal for beaches and shorelines to erode during stormy winter months along the US West Coast. But add to this normal pattern a strong El Niño—which brings increased wave energy—and erosion can be especially severe. This is precisely what happened when a very strong El Niño struck the West Coast during the winter of 2015/2016.
The 2015/2016 El Niño is the subject of a recent paper published in Nature Communications. The paper, whose co-authors include CIRC coastal researchers Peter Ruggiero and Katherine Serafin, examines how the El Niño of 2015/2016 affected both ocean wave patterns at near-coast buoys and shoreline erosion at 29 beaches along the US West Coast. Among their key findings, the researchers note that the El Niño resulted in the highest winter beach erosion on record for the West Coast. (Yes, you read that correctly.) However, this finding, while startling, is not surprising.
The El Niño of 2015/2016 was one of the three most powerful on record (dating back to 1871), and that power pummeled our region’s beaches. The El Niño’s waves, the researchers discovered, carried about 50 percent more energy than normal. What’s more, the researchers note, the off-shore buoys recorded one of the most energetic single wave events in recorded history when monster waves struck buoys on December 10th and 11th, with maximum wave heights ranging from 39 to 62 feet off the Oregon coast.
Because bigger waves equal more erosion, the West Coast suffered the highest winter beach erosion—what researchers refer to as shoreline retreat—ever measured. (Yes, we’re stating this finding twice, but it really deserves to be stated twice.)
Southern and central California suffered the worst erosion, with shorelines retreating four to five times more than in a mild winter. (The mild winter in this case was the winter of 2014/2015, which was used in the study for comparison.) At the same time, northern California and Washington experienced double the shoreline retreat. Oregon, by contrast, got off relatively lucky.
Levels of erosion for Oregon’s beaches during the El Niño winter of 2015/2016 surpassed levels for the El Niño-free winter of 2014/2015 by only 30 percent. According to the authors, Oregon was largely spared because of steady beach accretion, or growth, since the 2009/2010 El Niño. The state also experienced a couple of mild winters leading up to the recent El Niño, which also helped.
Another Glimpse into Our Future?
As our planet warms, research suggests we will see not only sea level rise, but also losses in some areas to the natural sediment supply that yearly rebuilds our West Coast beaches following their winter pummeling.
Both sea level rise and sediment loss are expected to increase the severity of coastal hazards, such as erosion and flooding, that events like the 2015/2016 El Niño tend to precipitate. And the 2015/2016 El Niño, much like the drought of 2014/2015, could provide a kind of glimpse into our climate-changed future.
To take just one example, the background coastal sea levels were one quarter to one and one half feet above normal during the winter of 2015/2016. These levels are the expected global mean sea level rise projected to happen during the next few decades. In other words, the severity of shoreline retreat seen during the winter 2015/2016 is expected to happen even during winters without strong El Niño in the not-to-distant future.
Let’s consider one last factor noted by the researchers.
Winter precipitation in southern California is expected to decrease. This implies less sediment discharge from rivers and less beach rebuilding for the state’s southern shoreline. This will make the southern California coast more susceptible to greater shoreline retreats. By contrast, the winter climate of Oregon and Washington is projected to be wetter, so reductions in sediment supply due to climate change alone is not anticipated in the Northwest.
STUDY: Nature Communications.
Citation: Patrick L. Bernard, Daniel Hoover, David M. Hubbard, Alex Snyder, Bonnie C. Ludka, Jonathan Allan, George M. Kaminsky, Peter Ruggiero, Timu W. Gallien, Laura Gabel, Diana McCandless, Heather M. Weiner, Nicholas Cohn, Dylan L. Anderson, and Katherine A. Serafin. (2016). “Extreme oceanographic forcing and coastal response due to the 2015-2016 Niño.” Nature Communications. doi: 10.1038/ncomms14365
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