In the future, New York could be hit harder by flooding than other coastal cities in the United States. 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. With more than a million buildings in New York City, the city faces a fate similar to that of Venice, Rotterdam and Jakarta. While the skyscrapers built on rock hardly sink, areas closer to the coast with softer subsoil are much more affected. This was calculated by a group led by geophysicist Tom Parsons from the United States Geological Survey in Menlo Park, California. in the journal Earth’s Future.
The four-person team estimates the buildings’ weight to be around 764 million tons. In addition to the weight, the type of soil is also responsible for the sinking of the city. “The surface geology of New York City is very complex,” the authors write, “because it is made up of various units including sand and beach deposits, boulder clays, and bedrock.” All of these types of soil have a different settling behavior. Above all, loamy soils and artificial embankments, which are common in Brooklyn, among other places, are prone to subsidence.
The scientists warn against a careless approach to the development of the city
Parsons and colleagues estimate that loamy soil and artificially filled areas would have a subsidence potential of 7.5 to 60 centimeters, 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.
And as the city slowly moves down, the sea level rises. Since In 1950, the water level on the coast of New York State rose by almost 23 centimeters gone up. Overall, the threat of sea level rise along the east coast of the United States is about three to four times higher than the global average.
This, in combination with the sinking ground and the increasing intensity of hurricanes, can lead to severe flooding. Only 2021 has hurricane Ida and the associated heavy rainfall showed that the city’s drainage systems could not cope with these enormous amounts of water. If undesigned buildings are repeatedly exposed to salt water, the materials such as steel and concrete will be structurally weakened over time.
The scientists warn against a careless approach to the development of the city. So be after the hurricane sandy 90 percent of buildings in flood-prone areas are not built to flood-prone standards. The extraction of groundwater could lead to further lowering. In addition, the East River and the Harlem River hardly bring any sediment into the port of New York. 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.