Already struggling with a problem of potholes linked to climate change, New York City is gradually sinking in water due to the weight of its skyscrapers.
This is the conclusion of a May report from the United States Geological Survey titled “The weight of New York City: Possible contributions to subsidence from anthropogenic sources.”
The report, which you can read here, indicates that the southern tip of the borough of Manhattan is vulnerable to natural disasters in a study. About 8.4 million people live in New York City, which is sinking 1-2 mm/year as sea levels rise, which puts the city at the same sinking rate as Venice, Italy.
Urban subsidence can be caused by groundwater withdrawal, natural soil compaction, tectonic effects, diversion of normal sediment accumulation, and the weight of cities themselves, the report says.
“New York City faces accelerating inundation risk from sea level rise, subsidence, and increasing storm intensity from natural and anthropogenic causes,” found the study, which calculates the mass of all buildings in New York City and model the subsidence caused by the pressure they exert on the Earth.
It also emerges that the East Coast city faces significant challenges from flood hazard. The threat of sea level rise is, according to the government researchers, four to five times higher than the global average along the Atlantic coast of North America.
“Post-glacial isostatic effects are projected to cause between 500–1,500 mm of subsidence by 2100. Much of lower Manhattan lies between 1 and 2 m in elevation above sea level, and measured subsidence from Global Positioning System (GPS) there is 2.1 mm/year,” the report says.
Rising Seas + Urbanization
The study chronicles the passage of two recent hurricanes that killed many people and caused heavy damage in the Big Apple to illustrate the dangers that await the huge urban center, including the boroughs of Brooklyn and Queens.
“In 2012, Hurricane Sandy forced sea water into the city, whereas heavy rainfall from Hurricane Ida in 2021 overwhelmed drainage systems because of heavy runoff within the mostly paved city,” it says, adding that the combination of tectonic and anthropogenic subsidence, sea level rise, and increasing hurricane intensity imply an accelerating problem along coastal and riverfront areas.
“Repeated exposure of building foundations to salt water can corrode reinforcing steel and chemically weaken concrete, causing structural weakening,” the government researchers warn, adding that New York is ranked third in the world in terms of future exposed assets to coastal flooding.
About 90% of the 67,400 structures in the expanded post-Hurricane-Sandy flood risk areas have not been built to floodplain standards, according to the report whose goal is to raise awareness that every additional high-rise building built at coastal, river, or lakefront settings could contribute to future flood risk, and that mitigation strategies may need to be included.
“New York is emblematic of growing coastal cities all over the world that are observed to be subsiding” which means that “there is a shared global challenge of mitigation against a growing inundation hazard,” the study warns.
Other Major Cities Sinking
Besides the City That Never Sleeps and Venice, other major cities around the world are also sinking at an equally alarming rate, according to the researchers. Projected sea level rise poses a clear threat to coastal cities, with “an expected increase of 200–600 mm by 2050 worldwide.” Globally, populations who live in subsiding cities will, the report says, face rising seas at rates up to four times faster than stable regions.
“Increasing urbanization will likely exacerbate subsidence by groundwater extraction and/or construction density, which combined with accelerating sea level rise implies a growing flood hazard in coastal cities,” the government researchers predict. “As these trends continue it will be important to be mindful of accompanying mitigation strategies against inundation in growing coastal cities.”