The total weight of buildings in New York City of 764 million tons pushes the U.S. metropolis into the sea and increases the risk of flooding.
New York – The city that never sleeps faces a problem. Sea level rise due to climate change is already a risk for coastal places. In New York, there is another factor: the concrete jungle that forms the unique skyline of the "Big Apple" of the USA pushes the city into the ground. As a result, the probability of being affected by flooding increases even more than in other coastal cities.
A team of researchers from the United States Geological Survey in California has calculated an average of one to two millimeters of subsidence per year. The subsidence of cities such as New York into the ground therefore depends on both the buildings and the subsoil itself. While skyscrapers standing on rock hardly sink, the subsoil of areas closer to the coast is often made of softer material and thus much more severely affected.
New Atlantis? New York sinks more sharply due to its skyline
In 2012, Hurricane Sandy caused parts of the metropolis to be flooded by seawater. The heavy rainfall from Hurricane Ida also caused the sewage system to overflow in 2021, with parts of the city also under water. According to studies on climate change, hurricanes are likely to occur more frequently in the New York area in the future, according to information from the German Press Agency (dpa). In addition, sea-level rise on the U.S. East Coast could be three to four times greater than elsewhere in the world.
The tall, heavy buildings of the skyline increase the risk of flooding in addition to these risk factors. In modelling and estimating, the research team put the total weight of buildings in New York City at 764 million tonnes.
The tall heavy buildings in New York City increase the risk of flooding. © Imago/Wirestock
USA: In addition to New York City, Staten Island is also sinking sharply
The specific subsidence rate depends, among other things, on the condition of the soil. According to the study, clay soils and artificially filled areas have a subsidence potential of 7.5 to 60 centimetres due to development, with an average value of a good 29 centimetres. Other soils are less susceptible to yielding to the load, with averages of 6 to 12 centimeters. For rock, the researchers determined a subsidence potential of 0 to 0.5 centimetres. Because with this subsoil, the earth deforms immediately after construction, after which hardly any more.
In addition, there is a natural subsidence of the ground in the New York area, which still dates back to the last ice age. The building load only contributes to the reduction, the authors emphasize. Also in the north of Staten Island, where the building load is low, strong subsidence had been observed.
New York – 90 percent of buildings not built for flooding
The scientists warn against a careless approach to the development of the city. For example, after Hurricane Sandy, 90 percent of buildings in flood-prone areas were not built according to floodplain standards. The extraction of groundwater could lead to further subsidence.
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Because of the replenishment of tributaries, the East River and the Harlem River hardly bring any sediment into New York Harbor. This makes the city more susceptible to flooding by northeasterly winds and hurricanes, the geologists write. Lower Manhattan is likely to be particularly affected: The southern tip of the central district is just one to two meters above sea level. (NA/dpa)