Climate scientists already know that the east coast of the United States could see around one foot rise in sea level by 2050, which will be catastrophic on its own. But they are just beginning to take a hard look at a “hidden vulnerability” that will make things worse: The coast is also sinking. It’s a phenomenon known as subsidence, and it’s about to make sea level rise even more dangerous, both for people and coastal ecosystems.
new research published In the diary nature communications finds that the Atlantic coast, home to more than a third of the US population, is falling several millimeters per year. In Charleston, South Carolina, and the Chesapeake Bay, it is up to 5 millimeters (one-fifth of an inch). In some areas of Delaware, it’s as much as double.
Five millimeters of annual sea level rise along a stretch of coastline, plus 5 millimeters of subsidence there, is effectively 10 millimeters of relative sea level rise. Cities on the Atlantic coast are already suffering persistent floodingand the deluge it will only get worse As they sink as the seas rise. However, high-resolution subsidence data like this is not yet taken into account for coastal hazard assessments. “What we want to do here is raise awareness about this missing component, which according to our analysis actually makes vulnerability in the near future much worse than what you would expect from sea level rise alone,” says Manoochehr Shirzaei, a Virginia Tech environmental safety expert and co-author of the new paper.
The main cause of the dramatic subsidence of the land is the excessive extraction of groundwater, which makes the land collapse like an empty water bottle. In San Jose, California, this has reduced elevation by as much as 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 Shirzaei. previous investigation. Parts of Jakarta are sinking 10 inches a yearforcing Indonesia to move your capital elsewhere. Oil extraction also causes subsidence, a particularly acute problem in the Houston-Galveston area. And landfills or sediment along shorelines can also settle over time.
While scientists knew that the US coastlines are sinking, they didn’t have much data to show local differences in rates. Subsidence varies significantly 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 safety expert at Virginia Tech, used data from a highly sensitive satellite that was sending radar signals back to Earth, then analyzed what bounced back to determine coastal deformation. They did this during the years 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 become more vulnerable to flooding as elevation falls. They also found that most cities on the Atlantic coast experience more than 3 millimeters of subsidence a year, including Boston and New York City. As the elevation drops, it destabilizes above ground infrastructure such as buildings and roads, as well as buried pipelines and cables.
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