According to recent research, New York City is sinking under the cumulative weight of all of its buildings.
This slow process might cause problems for a metropolis whose sea level has been rising more than twice as fast as the world average — and is expected to climb by eight to 30 inches by 2050, reports CNN.
Furthermore, experts predict that the human-caused climate crisis will result in more frequent and intense rainfall events such as nor'easters and hurricanes, it said.
“We’re a ways off from the ocean simply moving in,” said lead study author Tom Parsons, a research geophysicist at the US Geological Survey. “But we’ve had a couple of major hurricane events with Sandy and Ida in New York where heavy rainfall caused inundation in the city, and some of the effects of urbanization have allowed water to come in.”
The article, published in the journal Earth's Future, intends to demonstrate how high-rise structures in coastal, riverbank, or lakefront locations may contribute to future flood risk, and that mitigation measures should be implemented to prevent the potentially dangerous effects.
Sinking city risks — and a mystery
The researchers computed the mass of the 1,084,954 structures in New York City's five boroughs at the time, estimating that they weighed nearly 1.68 trillion pounds (762 billion kilograms) – roughly 1.9 million fully loaded Boeing 747-400s, the report also said.
The research team afterwards used simulations to evaluate the impact of that weight on the ground, which they compared to satellite data revealing actual surface geology. This analysis revealed how fast the city is sinking: “The average is about 1 to 2 millimeters a year, with some areas of greater subsidence that are up to about 4½ millimeters a year,” Parsons said.
Subsidence is the technical word for the sinking or settling of the Earth's surface caused by natural or man-made factors. According to a research published in September 2022, 44 of the 48 most populous coastal towns have parts that are sinking faster than sea levels are rising. The new technique of this current study is to consider the weight of New York City's skyscrapers and how they contribute to the sinking of the area underneath them, added the report.
However, the structures are not entirely to blame for the disaster. “We could see some correspondence where there’s construction on very soft soils and artificial fill,” Parsons said. “Other places, we see subsidence that’s difficult to explain. And there’s a lot of different causes of it, such as post glacial relaxation that happened after the last ice age, or groundwater pumping.”
According to the study, several sections of lower Manhattan, Brooklyn, and Queens are sinking at a quicker than average pace.
“Some of that seems to correspond with construction projects going on,” Parsons said. “But we also see subsidence on the north end of Staten Island that I can’t figure out an explanation for, and I’ve looked into all kinds of different things — so that still remains a mystery.”
Mitigating risk around sinking cities
According to the study, subsidence can cause floods even before sea level rise, and not just in New York City. “It’s a global issue. My co authors from the University of Rhode Island looked at 99 cities around the world, not only coastal but inland as well, and the vast majority of them have subsidence issues,” Parsons said, citing Jakarta as an example which is sinking so quickly that the Indonesian government is contemplating to relocate the country's capital.
“We know that global sea levels are rising and shorelines are changing, and that it is critical to understanding the impact of human activities, such as greenhouse gas emissions, on our warming world,” said geophysicist Sophie Coulson, a postdoctoral fellow at Los Alamos National Laboratory who was not involved in the study. “This research takes a look at an important human factor that has only recently come into focus — the effect of urban building loads on coastal land subsidence.”
The scientists, she continued, employ a sophisticated combination of computer modeling, satellite observations, and GPS data to estimate the short- and long-term sinking rates of different regions of the city and pinpoint the places most at risk.
“New York City is among the most densely populated coastal areas in the world, with a large portion of its critical infrastructure constructed in low-lying coastal areas,” she said.
“Understanding how and why the landscape is changing, and identifying areas most vulnerable to flooding is essential for making the right preparations to mitigate future sea level rise.”