NASA Team Cites Rising Waters and Falling Ground Levels Downtown
A new study from a team of NASA scientists finds that sea-level rise adjacent to Lower Manhattan has accelerated precipitously in the first quarter of the 21st century. An analysis published recently in the peer-reviewed journal Science Advances by a team of researchers from NASA’s Jet Propulsion Laboratory in Southern California and Rutgers University, says, “during the 20th century, relative sea level at the Battery tide gauge in Manhattan, New York City increased at a rate of about 3.1 mm/year. From 2000 to 2022, that rate has increased to 4.4 mm/year.” This amounts to a 42 percent increase in the rate of rising water between this century and last.
The same report noted that while local waters are rising, some land in the New York area is falling, due to subsidence, a process by which softer or looser ground can become compressed over time. One of these subsidence “hot spots” is the southern portion of Governors Island, which is built on 38 million square feet of rocks and dirt from early 20th century subway excavations. This part of Governors Island is sinking at approximately 3.4 millimeters per year, according to the report.
These measurements were taken using a remote sensing technique called interferometric synthetic aperture radar (InSAR). The approach combines two or more three-dimensional observations of the same region to reveal surface motion or topography.
The study found that the average subsidence for the New York metropolitan area as a whole is roughly 0.06 inches per year, or “about the same amount that a toenail grows in a month,” according to a NASA spokesperson.
These findings are broadly consistent with a May report from a team of scientists at the U.S Geological Survey (USGS) and the Graduate School of Oceanography at the University of Rhode Island, which indicated that the ground of Lower Manhattan might sink by as much as two feet before the end of this century.
Both studies are supported by an annual review from the National Oceanic and Atmospheric Administration (NOAA), the federal scientific agency responsible for study of oceans, major waterways, and the atmosphere, which predicts that Lower Manhattan will face increasingly frequent flooding in the decades to come.
That 2022 edition of the NOAA report, “Global and Regional Sea Level Rise Scenarios for the United States,” found (among other projections) that local sea levels will likely rise 19 inches between 2005 and 2060, compared to a nationwide average of ten to 12 inches. The same report predicts that the local occurrence of “extreme-water level events” (defined as water cresting five feet, six inches above the highest ordinary tide) will occur four to five times a year during that interval.