Below is New York’s JFK Airport. Note the red hotspots of high subsidence versus the blue-green of more moderate elevation changes. The airport’s average subsidence rate is 1.7 millimeters per year (similar to LaGuardia and Newark airports), but throughout JFK it varies between 0.8 and 2.8 millimeters per year, depending on the exact location.
This type of uneven settlement can also occur in much smaller structures, such as buildings, where one side can fall faster than the other. “Even if it’s just a few millimeters a year, it can cause cracks to form along the structure,” Owenhen says.
The study found that land subsidence is highly variable both regionally and locally on the Atlantic Coast, due to regional differences in geology and topography, as well as different rates of groundwater pumping. The problem appears to be particularly troubling in some communities, such as Virginia Beach, where 451,000 people and 177,000 properties are at risk. Baltimore, Maryland has a population of 826,000 people and 335,000 properties, while New York City (Queens, Bronx, and Nassau) has a population of 5 million people and 1.8 million properties.
Therefore, there are two elements to addressing the problem of land subsidence. That means taking high-resolution data like this study and combining it with groundwater data. “Subsidence is very spatially variable,” Snyder said. “If we can understand the details of where groundwater extraction is actually impacting and demonstrate the need to change the management of that water, we can reduce future subsidence.”
Sirzaei emphasizes that the time to act is now. Combating land subsidence is like treating a disease. Diagnosing and treating problems now will reduce your expenses and save you money later by avoiding disaster. “This type of data and research can become a critical component of health systems for infrastructure management,” he says. “Like cancer, if diagnosed early, it can be cured. But if you delay, you will be investing a lot of money and the outcome will be uncertain.”