Major cities all along the US Atlantic coast are sinking at an alarming rate, with some areas descending faster than global sea levels are rising. The combination of sinking land – or subsidence – and ascending water levels could result in catastrophic damage to urban centers in the near future, warn the authors of a new study.
The researchers analyzed satellite radar data provided by the United States Geological Survey in order to measure vertical land motion (VLM) up and down the east coast from 2007 to 2020. Using this information, the study authors were able to create high-resolution land subsidence maps, revealing which areas are sinking and how fast.
Results indicate that up to 2.1 million people currently live in regions that are sinking by 2 millimeters (0.08 inches) a year, with 867,000 properties located in these areas. Out of the 172 counties examined, seven to 43 are descending by around 5 millimeters (0.2 inches) a year – which is greater than the current 4-millimeter (0.16-inch) annual rise in sea levels.
“We know to some extent that the land is sinking,” said study author Manoochehr Shirzaei in a statement. “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.”
Exactly how much of a threat this poses to people residing in these spots is unclear, although the researchers write that “a subsidence rate of more than a few millimeters per year could cause concern, particularly in densely populated areas or areas with essential facilities like hospitals, schools, or transportation hubs.”
“Here, the problem is not just that the land is sinking,” added lead author Leonard Ohenhen. “The problem is that the hotspots of sinking land intersect directly with population and infrastructure hubs.”
“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 millimeters per year. The effects of these right now and into the future are potential damage to infrastructure and increased flood risks."
Among the major metropolitan areas exposed to subsidence rates above 1 millimeter (0.04 inches) per year are New York City, Baltimore, Newark (New Jersey), and numerous sites in the state of Virginia. As land sinks in these areas, the risk of coastal flooding increases, while damage to building foundations, roads, and other essential infrastructure also becomes a threat.
The study is published in the journal PNAS Nexus.