Major cities on the US Atlantic coast are sinking, in some cases as much as 5 millimeters per year, a new study shows.

The research from Virginia Tech and the US Geological Survey confirms the decline at the ocean’s edge well outpaces global sea level rise.

Particularly hard hit population centers such as New York City and Long Island, Baltimore, Virginia Beach, and Norfolk are seeing areas of rapid “subsidence,” or sinking land, alongside more slowly sinking or relatively stable ground, increasing the risk to roadways, runways, building foundations, rail lines, and pipelines.

“Continuous unmitigated subsidence on the US East Coast should cause concern,” says lead author Leonard Ohenhen, a graduate student working with Manoochehr Shirzaei, associate proifessor at Virginia Tech’s Earth Observation and Innovation Lab. “This is particularly in areas with a high population and property density and a historical complacency toward infrastructure maintenance.”

Shirzaei and his research team pulled together a vast collection of data points measured by space-based radar satellites and used this highly accurate information to build digital terrain maps that show exactly where sinking landscapes present risks to the health of vital infrastructure.

Using the publicly available satellite imagery, Shirzaei and Ohenhen measured millions of occurrences of land subsidence spanning multiple years. They then created some of the world’s first high resolution depictions of the land subsidence.

These groundbreaking new maps show that a large area of the East Coast is sinking at least 2 mm per year, with several areas along the mid-Atlantic coast of up to 3,700 square kilometers, or more than 1,400 square miles, sinking more than 5 mm per year, more than the current 4 mm per year global rate of sea level rise.

“We measured subsidence rates of 2 mm per year affecting more than 2 million people and 800,000 properties on the East Coast,” Shirzaei says. “We know to some extent that the land is sinking. Through this study, we highlight that sinking of the land is not an intangible threat. It affects you and I and everyone, it may be gradual, but the impacts are real.”

In several cities along the East Coast, multiple critical infrastructures such as roads, railways, airports, and levees are affected by differing subsidence rates.

“Here, the problem is not just that the land is sinking. The problem is that the hotspots of sinking land intersect directly with population and infrastructure hubs,” says Ohenhen. “For example, significant areas of critical infrastructure in New York, including JFK and LaGuardia airports and its runways, along with the railway systems, are affected by subsidence rates exceeding 2 mm per year. The effects of these right now and into the future are potential damage to infrastructure and increased flood risks.”

For the study, published in the Proceedings of the National Academy of Sciences , the researchers measured how much the land along the East Coast has sunk and which areas, populations, and critical infrastructure within 100 km (about 62 miles) of the coast are at risk of land subsidence. Subsidence can undermine building foundations; damage roads, gas, and water lines; cause building collapse; and exacerbate coastal flooding—especially when paired with sea level rise caused by climate change.

“This information is needed. No one else is providing it,” says coauthor Patrick Barnard, a research geologist with the USGS. “Shirzaei and his Virginia Tech team stepped into that niche with his technical expertise and is providing something extremely valuable.”

Source: Virginia Tech

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