The weight of New York City’s 1.1 million buildings causes the city to slowly sink, which can be seen in the cracks that form along bridges and other structures.
New York City is the most populous city in the United States, with 8.8 million people as of 2020. The sheer number of buildings to support all those residents, work, and everyday lives really adds up. New research published May 8 in Earth’s Future suggests that sea level rise at worst on an open coastline could reach 0.39 meters and that 32% of the population in all US coastal cities is below the “Minimum Sea Level Risk Boundary” of a probability of 0.9 meters per year, raising concerns about related climate change…
“In terms of concerns about global sea level rise, generally the idea most people have is that the ice is melting and that changes sea levels,” says Jacky Austermann, a geophysicist at Columbia University, who does not was involved in the study. the new search. But “it’s just a part of the contribution to sea level rise in a given location”. Ground subsidence, which can occur for a variety of reasons, is another important factor to consider, he says. “If you’re on the coast, either the land is sinking or the sea level is rising, they both cause the same amount of flooding,” adds Austermann.
new york sinks
The researchers wanted to learn more about how a city’s weight might play a role in local sea level rise, and New York City provides a lot of data for analysis. “We just imported all this mass”, says lead author Tom Parsons, geophysicist at the US Geological Service. UU. “In lower Manhattan, it almost seems like a mountain chain that we built there, so all that weight is also pressing down”.
For research purposes, the researchers looked at how much weight each building in New York City could support. In fact, there are over 1 million buildings in the five boroughs and they all weigh A LOT! Parsons and his team took a map of the city and used a database already populated with the total height of each building to help them get started. They used building codes to estimate the weight in each grid and came up with a total of 764 billion kilograms (1.68 trillion pounds) for all buildings in New York City. “It’s not a perfectly accurate weight, but it gives us a rough idea of what the concentration of buildings is,” says Parsons. (For simplicity, the team did not account for the weight of roads and sidewalks.)
Next, the researchers mapped the geology of New York City. In some neighborhoods, like midtown Manhattan, there is clayey soil that sits close to the surface and compresses easily. Unlike other areas of the city, some areas like Brooklyn have artificially expanded their physical footprint by filling in land and building. This made its properties safer against weight-induced shedding. Artificial filler varies in type, but it can be compressed very easily. It can be difficult to assess the condition of a soil and then measure the appropriate amounts of backfill material, but there are certain considerations that must be made when calculating backfill.
The researchers fed their building and soil type distribution maps into a set of models designed to predict how different geologies respond to pressure. These results made it possible to detect areas where subsidence due to the city’s own weight can be especially frequent.
Is two millimeters a year too much?
Satellites collect data and track how the land surface changes over time, letting you know how low your city is sinking. Using satellite data, they found that the city was sinking an average of one to two millimeters per year. Note that the models show subsidence in areas not accounted for by urban weight.
The researchers found that areas where construction weight is concentrated on looser soils are likely to contribute substantially to ground subsidence. The study is not intended to be a definitive analysis, but rather a first step towards understanding how cities around the world may be contributing to the sea level rise they are experiencing.
Researchers are attributing different potential factors that cause sea level rise, and this could help us as we continue on the path to finding solutions to climate change. “As (the study authors) point out…, the comparison between data and models is tricky. There are a lot of things we don’t understand,” says Austermann, adding that the study essentially provides a rough estimate of sinking urban weight rather than an exact estimate.
One of the limitations of this research is that scientists have not been able to mimic the city’s 400-year development. They were unable to fully capture and project their weight and therefore any related subsidence could occur in the coming years.
“They model the overall subsidence of an initial load of all buildings as if they were somehow built at the same time, magically appearing in uncompacted soil or rock simultaneously,” says Cathleen Jones, a physicist at the Jet Propulsion Laboratory (JPL). ). from NASA. Jones is not involved in the new research that studies subsidence and other types of land deformation. He specializes in using satellite data, which can provide better information for the study.
“Of course, the buildings were built at different times, so that part of the model is not realistic,” he says, adding that this is his opinion, not NASA or JPL’s. Jones notes that the team’s long-term sink estimates are more realistic and match satellite observations.*
This study is a useful reminder of both the challenges and opportunities that lie ahead in the field. The new findings may not apply to all regions, but they are important for understanding issues such as those faced coastal cities from all over the world.
If we don’t adapt to living in a coastal area soon, it could have devastating consequences. By 2050, nearly 70% of the world is expected to live in a city. This combination means that cities that are already vulnerable to sea level rise may also be struggling under their own weight, and while much of New York City benefits from a solid foundation, other cities are in a more dire situation. difficult.
“Most coastal cities in the world are expanding significantly,” says Parsons. “It’s likely to be a growing concern given this kind of shift in the distribution of people.”
*Editor’s Note (5/30/23): This paragraph was updated after publication to reflect the full scope of Cathleen Jones’ comments on the accuracy of the study results.
Meghan Bartels is a science journalist and news reporter for scientific american who lives in New York City.