A new study published in the journal Earth's Future has tracked subsidence, or the settling of sediments, underneath the Big Apple and found the city is sinking an average of 1 to 2 millimeters per year. However, some parts are sinking even faster.
The port city of 8.2 million people, which sits at the mouth of the Hudson River and also straddles the East River and Harlem River, is already barely above sea level. When the city sustained a direct hit by Hurricane Sandy in 2012, the sea swelled above its embankments and inundated city streets, with water pouring into the subway system and myriad underground tunnels as well.
As sea levels continue to rise as a consequence of global warming, the city’s steady sinking is likely to become an even bigger problem.
"The point of the paper is to raise awareness that every additional high-rise building constructed at coastal, river, or lakefront settings could contribute to future flood risk," said geologist Tom Parsons of the United States Geological Survey, who wrote the study with other colleagues at the University of Rhode Island.
Parsons' team calculated the cumulative weight of Gotham’s buildings at roughly 1.68 trillion pounds - and that’s not even including roads, sidewalks, bridges, railways, and other parts of the city. They also looked at the soil substrates beneath the city, finding clay-rich soils alongside sand and silt - all prone to subsidence. There were also smaller bedrock outcrops, which stand up to the weight of construction much better.
The Big Apple has more than 6 000 high-rise buildings, 274 of which are skyscrapers standing over 492 feet tall. Those include towering structures like the Empire State Building, 30 Hudson Yards, and One World Trade Center, all of which have more than 100 floors.
"New York is emblematic of growing coastal cities all over the world that are observed to be subsiding, meaning there is a shared global challenge of mitigation against a growing inundation hazard," the researchers said.
Indeed, New York is just one of many coastal metropolises facing a sinking problem amid rising sea waters: the Indonesian capital of Jakarta, for example, is sinking at a stunning rate of 11 centimeters per year. By 2050, one-quarter of the city is expected to be underwater. Jakarta is home to some 10.5 million people.