New research uses decades of satellite data to show how climate variability—particularly El Niño and La Niña cycles—drives shoreline change along the North American West Coast.
The research, led by the Université de Toulouse and partners, highlights how coastal erosion and shoreline movement vary significantly with time and with latitude. By analyzing waterline positions—where land meets ocean—between 1997 and 2022, scientists found that in the Pacific Northwest, seasonal waterline movements often exceed 25 meters, while shifts in Southern California and farther south rarely top 10 meters.
The driving forces behind these changes also vary by region. Wave power is the dominant force in the northern parts of the coast, while farther south, sea-level fluctuations and southern hemisphere swell become important. This reflects a transition in how wave climate affects coastal processes from north to south.
“This paper is the synthesis of [lead author Marcan Graffin’s] many separate efforts, from developing satellite shoreline-detection algorithms, to generating large-scale data sets, and then analyzing them alongside climate data. We’ve learned a great deal about the nuances of shoreline variability on the U.S. West Coast from Marcan’s work,” said USGS Research Oceanographer Dr. Sean Vitousek, a co-author of the study.
In addition, the study examines the outsized influence of the El Niño–Southern Oscillation (ENSO), the recurring climate pattern that swings between warm (El Niño) and cool (La Niña) phases in the Pacific Ocean, on shoreline positions. During El Niño years, intense storm tracks shift southward, boosting wave energy and accelerating erosion from Southern California to Baja California Sur. La Niña events, on the other hand, are associated with smaller winter waves and mild shoreline accretion across the subregion.
However, farther north—from Northern California through the Pacific Northwest—the impacts of ENSO are less predictable. There, shoreline response depends on a complex blend of storm path changes, wave-energy intensity, and local geography.
These patterns help explain why some coastlines erode dramatically during strong El Niño winters while others seem to hold steady, demonstrating how regional climate signals interact with local coastal dynamics.
The study is one of the first to examine shoreline changes along such a large, diverse stretch of coast using a consistent satellite-derived dataset. The 25-year archive of shoreline imagery allowed researchers to tease out both seasonal and interannual trends—critical for anticipating how coastlines will respond to future climate extremes.
Read the study, Waterline responses to climate forcing along the North American West Coast, in Nature Communications: Earth & Environment.
