Rising seas, sinking cities: Land subsidence on the East Coast

A recent study highlights a concerning environmental issue facing the U.S. East Coast. In this region, land subsidence poses a severe risk to infrastructure, populations, and properties. 

The research team, led by Leonard O. Ohenhen, used radar satellite data to assess vertical land movement and its potential impacts.

Focus of the study

“Coastal regions, where most megacities are located, are on the front lines of climate change impacts and associated uncertainties,” wrote the study authors. 

“The coincidence of population migration toward low-elevation coastal areas and continued accelerating sea-level rise (SLR) will increase the future vulnerability of coastal communities worldwide.” 

“The impact of SLR-amplified hazards on coastal communities, such as flooding and erosion, dominates in global climate change discussions, with other coastal hazards, such as land subsidence (the lowering of land elevation) relegated to the background.” 

“Land subsidence, however, is a pernicious and growing problem on a global scale with more immediate hazards to coastal areas and often presents more pressing and localized challenges.”

The extent of the problem

The study revealed that a vast area of the U.S. East Coast is experiencing subsidence, with a smaller region of about 3,700 km2 sinking at an alarming rate of over 5 mm per year. 

The downward movement of land can lead to various hazards, such as damage to building foundations, roadways, and utility lines. It can also result in building collapses and intensify coastal flooding, particularly when combined with climate change-induced sea level rise.

Populations and properties at risk

Land subsidence rates of 2 mm per year are already impacting up to 2.1 million people and 867,000 properties along the East Coast. Several communities, including Norfolk and Virginia Beach in Virginia, Baltimore in Maryland, and areas within New York City like Queens, the Bronx, and Long Island, have over 60% of their land area subsiding. 

This phenomenon is not just a natural hazard but also a significant infrastructural challenge, affecting roads, railways, airports, and levees. Notably, New York’s JFK and LaGuardia airports have parts, including runways, sinking at more than 2 mm per year.

Causes and varied impacts

The causes of subsidence are primarily attributed to groundwater extraction and sediment compaction. However, the situation is complex, as some areas are actually rising due to the continent’s gradual rebound from the last glacial period. 

Around the Chesapeake Bay, this results in a patchy mix of rising and falling land, leading to medium–high risks of differential subsidence. This particular form of land subsidence can cause angular distortion, leading to structural damage over time.

Policy implications and future concerns

The study authors emphasize that while there’s no universally agreed-upon subsidence threshold that triggers policy action, the ongoing and unmitigated subsidence on the East Coast is alarming. 

This is especially true given the high density of population and properties, coupled with a general complacency towards infrastructure maintenance. The study highlights the need for immediate and strategic responses to mitigate risks and protect the affected communities.

The research is published in the journal PNAS Nexus.

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