2023-05-20 11:02:37
In the future, New York could be hit harder by flooding than other coastal cities. In addition to the rise in sea level due to climate change, the subsoil sinks by an average of one to two millimeters per year. The subsidence depends both on the development and on the subsoil itself. While the skyscrapers founded on rock hardly subside, areas closer to the coast with softer subsoil are much more affected. This is calculated by a team led by Tom Parsons from the United States Geological Survey in Menlo Park (US state of California). in the journal “Earth’s Future”.
In 2012, hurricane Sandy caused parts of the metropolis to be flooded by seawater. The heavy rainfall from Cyclone Ida in 2021 caused the sewage system to overflow, and parts of the city were flooded again. Studies show that climate change is likely to increase the number of hurricanes in the New York area, and sea level rise on the US East Coast could be three to four times higher than anywhere else in the world.
Various factors
And the high, heavy buildings in New York City also increase the risk of flooding. Using modeling and estimates, Parsons’ team determined the total weight of the buildings in New York City to be 764 million tons. The specific subsidence rate also depends on the soil types. 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.
Hurricane Sandy caused more severe flooding in the city in 2012.
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Image: dpa
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.
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 is likely to be particularly affected: the southern tip of the central district is just one to two meters above sea level.
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