New research has found that cities on the Atlantic coast of the United States are sinking as much as five millimeters every year, which is faster than sea level rise. This phenomenon, known as subsidence, is impacting many cities around the world, but this report has shown that the United States is also affected. Cities like New York, Baltimore, and Norfolk are home to millions of people, and while they sit on stable ground, the land is still sinking. The researchers noted that this could threaten infrastructure like railways, roads, building foundations, and pipelines. The findings have been reported in PNAS Nexus.
"Continuous unmitigated subsidence on the US East Coast should cause concern," said lead study author Leonard Ohenhen, a graduate student in the lab of Associate Professor Manoochehr Shirzaei at Virginia Tech. "This is particularly in areas with a high population and property density and a historical complacency toward infrastructure maintenance."
In this work, the researchers used publicly available data that has been collected by satellites over multiple years to generate terrain maps, which revealed where the land is sinking, and where it poses a risk. They found millions of cases in which land subsidence had occurred.
The high-resolution maps made by the investigators revealed a large area of the US East Coast that has been sinking by two millimeters or more per year. Some parts of the mid-Atlantic, which cover an area over 1,400 square miles are sinking over five millimeters every year. This exceeds the current rate of sea level rise, which is an average of four millimeters annually.
"We measured subsidence rates of two millimeters per year affecting more than 2 million people and 800,000 properties on the East Coast," Shirzaei said. "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."
There are also places where the subsidence is uneven. The researchers determined that many of areas where it is happening the fastest are directly under large populations centers or crucial locations. "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 two millimeters per year. The effects of these right now and into the future are potential damage to infrastructure and increased flood risks," said Ohenhen.
Sources: Virginia Tech, PNAS Nexus