“New York City Sinking Under the Weight of Its Skyscrapers: Impacts and Future Risks”

Reading time: 2 min — Spotted on Science Alert

New York is heavy. In total, the weight of its buildings reaches 764 billion kilograms. Supporting a million constructions, the Big Apple sinks a little more into the earth every year, while sea levels rise: a recent study, published in the scientific journal Earth’s Future, and co-authored by Tom Parsons , Pei-Chin Wu, Meng Wei and Steven D’Hondt, determined that the metropolis sank by one to two millimeters each year under the weight of its buildings.

This progressive subsidence, which is called “subsidence”, can usually be of tectonic or thermal origin or, in the case of New York, linked to an overload, that is to say that loads weighing on the ground push it even deeper.

“The aim of this article is to raise awareness that each new high-rise building built by the sea, river or lake could contribute to the risk of future flooding”write geologist Tom Parsons of the United States Geological Survey and his colleagues at the University of Rhode Island.

In fact, some parts of the city are sinking much more quickly, and this deformation could increase the risk of flooding, despite the construction of gigantic dykes to fortify the city.

The coming crash

In their study, Parsons and his colleagues considered only the mass of New York’s buildings and their contents, without calculating the additional weight that roads, sidewalks, bridges, and other paved areas of the city.

Clay-rich soils, such as those in New York, are particularly prone to subsidence, as are artificial embankments. The more elastic soils, also present in the complex geology of New York, tend to regain their shape after having absorbed the weight of a construction, and the bedrock, which serves as an anchor for many skyscrapers , move only slightly.

The increasing urbanization of the megalopolis, coupled with the drainage and pumping of groundwater, however risks aggravating the phenomenon of subsidence. “New York is emblematic of the expanding coastal cities around the world that are seen subsiding, which means there is a common global challenge of mitigating growing flood risks”, say the researchers. And indeed, New York is far from the only one to suffer from subsidence: Jakarta, the Indonesian capital, could be under water by 2050, parts of the city sinking by almost 11 centimeters per year. due to groundwater extraction.

Reducing greenhouse gas emissions remains the best way to limit future risks, whether to deal with rising waters or hurricanes, which previously harassed Manhattan in 2012 (Sandy) and 2021 (Ida ).