New York City is sinking under water under the weight of its own buildings much faster than the level of the world’s seas is rising. Because of this, the metropolis is at risk of flooding much faster than many other cities, a group of researchers from the US Geological Survey found out.
Sea level relative to New York is rising twice as fast as worldwide. According to forecasts, it will rise by 20-75 cm by 2050. “On average, New York City is sinking at a rate of 1-2 mm per year, but in some areas subsidence reaches 4.5 mm per year,” geophysicist Tom Parsons, one of the authors of the study, told CNN.
“New York City is in serious trouble due to the risk of flooding. The threat of sea level rise here is three to four times higher than the average along the Atlantic coast of North America. The 8.4 million residents of New York City, which is characterized by a high concentration of the population, may be at varying degrees of danger in the event of flooding, ”the study says.
Researchers calculated the mass of 1.08 million buildings in the five boroughs (boroughs) of New York that existed as of September 2022. It amounted to 762 million tons – this is equivalent to approximately 1.9 million fully loaded Boeing 747-400 aircraft.
A team of scientists then calculated the effect of this weight on the surface of the earth using computer simulations and satellite data. This analysis revealed the speed with which the largest metropolis in the United States is gradually sinking.
However, not all subsidence is due to the huge weight of buildings, says Parsons. “We understand subsidence in places where buildings are built on soft ground or artificial embankments. But there are areas where we are seeing subsidence, which is difficult to explain,” the expert explained.
According to him, some areas of New York can sink faster than usual for a variety of reasons: due to the pumping of groundwater, due to the so-called relaxation of the soil caused by the last ice age.
Among those areas that sink faster than others are the most densely populated boroughs of New York: Queens, Brooklyn, lower Manhattan. Parsons notes that this partly corresponds to the load from large and heavy buildings. But scientists also recorded subsidence of the northern part of Staten Island, the most remote and least populated area of the metropolis. And so far they can not find an explanation for this.
New York City’s accelerated sinking relative to sea level means that it risks being completely or partially flooded in the future. The authors of the study do not give accurate predictions of when this will happen – the time range is from tens to several hundred years, with the ongoing rate of subsidence. However, geophysicists note that other factors can also accelerate the flooding of the metropolis: extreme showers, hurricanes, which occur more often due to anthropogenic influence on the environment.
Parsons recalls that in recent years the city has been suffering more and more damage from natural disasters. For example, due to Hurricane Sandy in 2012, seawater from the bays flooded part of the city. And torrential rains during Hurricane Ida in 2021 knocked out drainage systems for several days.
The problem is not only that the streets of the metropolis may be under water in decades. In the much shorter term, there is a threat to the integrity of buildings.
“Repeated exposure of building foundations to salt water can corrode reinforcing steel and chemically weaken concrete, resulting in structural weakness,” explains Parsons. Despite the lessons of Sandy, many of New York’s skyscrapers built since 2012 haven’t taken these factors into account, he says.
The city ranks third in the world in terms of the number of objects that may be subject to flooding in the future, the study says. Of the 67,400 structures in flood-prone areas, 90% were built without standards for flooded terrain.
New York is far from the only coastal city to face this problem. The study found that nearly all of the world’s most populous coastal cities are sinking relative to sea levels faster than globally rising ocean levels.
“My co-authors at the University of Rhode Island studied 99 cities around the world — not just coastal, but inland — and the vast majority of them have subsidence problems,” Parsons said. As an example, he cited Jakarta, which is located in a swampy area and sinks so quickly due to groundwater that the Indonesian authorities intend to move the capital to another city.
As stated in the summary of the scientific article, its purpose is to draw attention to the problem and explain that each new skyscraper built on the coast of the sea, river or lake can increase the risk of future flooding. And also stimulate the development of a strategy to mitigate the impact of construction on soils.