“New York City’s Sinking Skyline: The Risk of Flooding and Climate Change”

The total weight of the buildings in New York City of 764 million tons pushes the US 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 locations. There is another factor in New York: the concrete jungle that forms the unique skyline of the “Big Apple” in the USA also presses the city into the ground. This increases the probability of being affected by flooding even more than in other coastal cities.

A research team from the United States Geological Survey in California calculates an average of one to two millimeters of subsidence per year. The subsidence of cities like New York depends both on the development and on 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 is therefore much more affected.

New Atlantis? New York sinks more due to its skyline

In 2012, hurricane Sandy caused seawater to flood parts of the metropolis. The heavy rainfall from hurricane Ida also caused the sewage system to overflow in 2021, and here too parts of the city were under water. According to studies on climate change, hurricanes are likely to occur more frequently in the New York area in the future German Press Agency (dpa). In addition, sea level rise on the US East Coast could be three to four times greater than anywhere else in the world.

The high, heavy buildings of the skyline increase the risk of flooding in addition to these risk factors. In modeling and estimation, the research team determined the total weight of buildings in New York City to be 764 million tons.

USA: In addition to New York City, Staten Island is also sinking sharply

The concrete subsidence rate depends, among other things, on the soil conditions. According to this, clay soils and artificially filled areas have a sinking potential of 7.5 to 60 centimeters due to development, with an average of a good 29 centimetres. Other soils are less prone to yielding under load, with average values ​​of 6 to 12 centimetres. The researchers determined a subsidence potential of 0 to 0.5 centimeters for rock. Because with this subsoil, the earth deforms immediately after construction, and then hardly any more.

In addition, there is a natural subsidence in the New York area that still stems from the last Ice Age. The authors emphasize that the building load only contributes to the reduction. Strong subsidence has also been observed in the north of Staten Island, where the building load is low.

New York – 90 percent of buildings not built for flooding

The scientists warn against a careless approach to the development of the city. After Hurricane Sandy, 90 percent of buildings in flood-prone areas were not built to flood-prone standards. The extraction of groundwater could lead to further lowering.

The East River and Harlem River bring little sediment to New York Harbor because of tributary fill-up. The geologists write that this makes the city more susceptible to flooding from northeast winds and hurricanes. Lower Manhattan in particular is likely to be affected: the southern tip of the central district is just one to two meters above sea level. (na/dpa)