Parts of the New York City metropolitan area are sinking and rising at different rates due to several factors ranging from land-use practices to long-lost glaciers, scientists from NASA’s Jet Propulsion Laboratory and Rutgers University found.
While the elevation changes seem small – fractions of inches per year – they can enhance or diminish local flood risk linked to sea level rise, they said.
LAND ELEVATION
The new study sheds light on the dynamic changes in land elevation within the New York City metropolitan area. These subtle shifts, though small in magnitude, have implications for local flood risk due to sea level rise.
Published in Science Advances, the study utilized interferometric synthetic aperture radar (InSAR) technology to track both upward (uplift) and downward (subsidence) vertical land motion across the metropolitan area from 2016 to 2023. These changes in elevation are attributed to a variety of factors, including historical land-use practices and geological processes dating back to the last ice age.
LOCAL FACTORS
Areas with prior modifications to the Earth’s surface, such as land reclamation and landfills, experienced significant motion. This is due to the ground becoming looser and more compressible over time beneath buildings.
GEOLOGICAL HISTORY
The area was once covered by a massive ice sheet approximately 24,000 years ago. About 24,000 years ago, a huge ice sheet spread across most of New England, and a wall of ice more than a mile high covered what is today Albany in upstate New York. Earth’s mantle, somewhat like a flexed mattress, has been slowly readjusting ever since. New York City, which sits on land that was raised just outside the edge of the ice sheet, is now sinking back down.
SUBSIDENCE RATE
On average, the metropolitan area is subsiding at a rate of about 0.06 inches (1.6 millimeters) per year, akin to the growth of a toenail in a month.
The researchers used data from the European Space Agency’s Sentinel-1 satellites and advanced data processing techniques to pinpoint neighborhoods and landmarks sinking at rates exceeding the average. Notable subsidence hot spots include LaGuardia Airport’s runway 13/31 and Arthur Ashe Stadium, which required construction modifications to combat subsidence.
UPLIFT AREAS
Additionally, the study identified areas experiencing uplift, notably in East Williamsburg, Brooklyn, and Woodside, Queens. The causes of these uplifts, including groundwater pumping and injection wells, warrant further investigation.
Understanding these local changes in land elevation is critical for flood mapping and planning, particularly as rising global sea levels lead to more frequent nuisance flood events and storm surges. The study emphasizes the importance of high-resolution estimates of land motion for cities like New York investing in coastal defenses and infrastructure in response to sea level rise.
“We’ve produced such a detailed map of vertical land motion in the New York City area that there are features popping out that haven’t been noticed before,” said lead author Brett Buzzanga, a postdoctoral researcher at JPL.
David Bekaert, a JPL scientist and lead investigator of the project, said that tracking local elevation changes and relative sea level can be important for flood mapping and planning purposes. This is especially critical as Earth’s changing climate pushes oceans higher around the world, leading to more frequent nuisance flood events and exacerbating destructive storm surges.
The research project, OPERA (Observational Products for End-Users from Remote Sensing Analysis), led by JPL, aims to provide detailed surface displacement data across North America, leveraging InSAR data from ESA’s Sentinel-1 satellites and the upcoming NISAR mission, set to launch in 2024. This information will aid in monitoring vertical land motion and other changes related to natural hazards.