A new study using satellite data has found that New York City is sinking at a relatively fast rate, with some urban areas sinking much faster than others. According to the team, one contributing factor is the sheer weight of the city's high-rise buildings.
The team, led by US Geological Survey research geophysicist Tom Parsons, looked at subsidence models, surface geology, and the Interferometric Synthetic Aperture Radar and Global Positioning System (satellite data).
"Geodetic measurements show a mean subsidence rate of 1–2 mm/year across the city that is consistent with regional post-glacial deformation, though we find some areas of significantly greater subsidence rates," the team explained in their study.
Part of the problem is urbanization itself.
"Cumulative pressure applied to the ground from large buildings contributes to subsidence not only from initial primary settlement caused by soil compression and reduction of void space, but also through potential secondary settlement caused by creep in clay rich layers that can continue indefinitely," the team explains.
The team calculated the total mass of the buildings in New York at 764,000,000,000 kilograms (1.68 trillion pounds), exerting pressure on the ground below. The geology of New York is complex, with a range of soils. The team writes that buildings on clay-rich soil and artificial fill "are especially prone to significant building settlement and clay models show the largest potential subsidence, ranging from −75 to −600 mm with a median of −294 mm at a sample point in lower Manhattan".
Other factors contributing to subsidence included hurricanes Sandy and Ida, and the team warned that repeat exposure of building foundations to seawater – from hurricanes or rising sea levels – can cause structural weakening, corroding the steal and weakening the concrete. These problems will only be exacerbated by the climate crisis and increased urbanization.
"Major cities around the world are expected to grow disproportionately relative to rural areas, with a projected 70 percent of the world's population living in cities by 2050," the team concludes. Major cities on every continent except Antarctica are observed to be subsiding, and the issue may be worsened as populations grow.
"Increasing urbanization will likely exacerbate subsidence by groundwater extraction and/or construction density, which combined with accelerating sea level rise implies a growing flood hazard in coastal cities. As these trends continue it will be important to be mindful of accompanying mitigation strategies against inundation in growing coastal cities."
The study was published in the journal Earth's Future.