More than 8 million people live in New York City (NYC), which has been observed to be sinking 1–2 mm/year.
1. Low-lying geography
While there are significant global concerns with sea level rising, especially for coastal cities — including NYC — some of the key factors contributing to the vulnerability of NYC’s sinking are its low-lying geography, densely populated coastal areas, and extensive infrastructure along the waterfront.
According to a scientific article published in Advancing Earth and Space Science, each year NYC has been losing 1–2 mm. The team calculated the mass of all buildings in NYC and modeled the subsidence caused by the pressure they exert on the Earth, with the support from satellite data.
The researchers started analysing the city’s weight, which included all of NYC’s buildings — 1,084,954 of them across all five boroughs. “We’ve just imported all this mass,” said lead author Tom Parsons, a geophysicist at the US Geological Survey.
In lower Manhattan, it almost looks like a mountain range that we’ve kind of built up there, so all that weight is also pressing down.
Tom Parsons, research lead author
Parsons and his colleagues mapped the city on a grid and consulted a database that included the footprint and total height of every building in the city. They used building codes to estimate the weight in each grid square —and came up with a total of 764 billion kilograms (1.68 trillion pounds) for all of NYC’s buildings. “It’s not a perfectly exact weight, but it gives us a rough idea of what the concentration of buildings is,” added Parsons.
The next step was to map the city’s geology. NYC is located on various types of bedrock, including granite, gneiss, and schist, which are generally stable. However, there are localized areas with softer soil and unconsolidated sediments, particularly in parts of Manhattan and Brooklyn, where the ground is more susceptible to settlement and sinking. It’s important to note, however, that while there have been reports of sinking buildings and infrastructure in specific locations, it does not imply that the entire city is sinking uniformly.
2. Global understanding
Ultimately, the study is meant not as a definitive analysis but as a first step in understanding how cities around the world may be contributing to the sea-level rise that threatens them. “As [the study authors] highlight…, the comparison between the data and the models is complicated. There’s a lot of things we don’t understand,” Austermann said, adding that the study essentially gives a rough estimate of subsidence from urban weight instead of an exact calculation.
“From a scientific perspective, this is an important study,” said Andrew Kruczkiewicz, a senior researcher at Columbia University’s Climate School, who was not involved in the research. Its findings could help inform policymakers as they draft ongoing plans to combat, or at least forestall, the rising tides.
3. Enhancing resilience
To address these challenges, NYC has undertaken various initiatives to enhance resilience and adapt to rising sea levels. One such initiative is the “NYC Climate Resiliency Design Guidelines,” which provides guidance to architects, engineers, and designers on incorporating resilience measures into infrastructure projects. The city is also investing in the construction of protective infrastructure, such as seawalls, flood barriers, and green infrastructure like wetlands and marshes, to absorb floodwaters.
The city is also working on long-term plans, such as the “NYC Comprehensive Waterfront Plan,” to ensure sustainable development along the coast and improve the city’s ability to withstand future sea level rise and associated flooding risks.
