As the sea level rises, the east coast also sinks

by The Insights

The climatologists already be aware that the east coast of the United States could see a sea level rise of about one foot by 2050, which would be catastrophic in itself. But they are just beginning to thoroughly measure a “hidden vulnerability” that will make matters worse: the coastline is also shipwreck. It’s a phenomenon known as subsidence, and it’s poised to make rising oceans all the more dangerous, both for people and for coastal ecosystems.

New research published in the journal Nature Communication finds that the Atlantic coast, home to more than a third of the US population, is shrinking by several millimeters a year. In Charleston, South Carolina, and the Chesapeake Bay, it’s up to 5 millimeters (one-fifth of an inch). In some parts of Delaware, it’s up to double.

Five millimeters of annual sea level rise along a stretch of coast, plus 5 millimeters of subsidence there, is actually 10 millimeters of relative sea level rise. the Atlantic are already suffering from persistent flooding, and the deluge will only get worse as it sinks as the seas rise. Yet high-resolution subsidence data like this is not yet considered for coastal risk assessments. “What we want to do here is really raise awareness of this missing component, which our analysis shows makes vulnerability in the near future much worse than you would expect from elevation alone. sea ​​level,” says Manoochehr Shirzaei, an environmental security expert at Virginia Tech and co-author of the new paper.

The main cause of dramatic land subsidence is the over-extraction of groundwater, causing the land to collapse like an empty water bottle. In San Jose, California, this reduced the elevation by 12 feet. The combination of sea level rise and subsidence could inundate up to 165 square miles of Bay Area coastline by 2100, according to previous research by Shirzaei. Parts of Jakarta are sinking 10 inches a year, forcing Indonesia to move its capital elsewhere. Oil extraction also causes subsidence, a particularly acute problem in the Houston-Galveston area. And landfills or sediments along the coasts can also settle over time.

Although scientists have been aware that US coasts are sinking, they haven’t had much data to show local differences in rates. Subsidence varies considerably even over short distances, given variations in the underlying geology and nearby human activity. For this new paper, Shirzaei and lead author Leonard Ohenhen, also an environmental security expert at Virginia Tech, used data from a highly sensitive satellite that sent radar signals to Earth, then analyzed what bounced back. to determine coastal deformation. They did this between 2007 and 2020, along 3,500 kilometers (2,200 miles) of the Atlantic coast.

The researchers found particularly intense subsidence in agricultural areas, where groundwater is extracted to feed crops, which in turn will be more vulnerable to flooding as elevation drops. They also found that most Atlantic coastal cities experience more than 3 millimeters of subsidence per year, including Boston and New York. As elevation decreases, it destabilizes above-ground infrastructure like buildings and roads, as well as buried pipes and cables.

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