Satellite images have confirmed widespread and accelerating land subsidence across multiple major cities along the US Atlantic coast, threatening vital infrastructure and coastal communities according to newly published research.
Accelerating Land Sinkage Detected Through Advanced Satellite Monitoring
Advanced analysis of high resolution satellite imagery published this week in the Proceedings of the National Academy of Sciences has revealed significant sinking of land in cities up and down the East Coast over the past few decades [1]. The study conducted by researchers at Virginia Tech utilized satellite-based Interferometric Synthetic Aperture Radar (InSAR) to quantify subsidence rates across the region between 2007-2021.
The radar technology allows precise measurements of changes in ground elevation over time. The latest InSAR data indicates substantial sinking of land in excess of global sea level rise, with particularly high subsidence rates detected in metropolitan regions critical to the economy, infrastructure, and national security of the United States.
| City | Max Subsidence Rate Detected 2007-2022 |
|---|---|
| Boston, MA | 8.1 mm/year |
| New York City, NY | 10.2 mm/year |
| Philadelphia, PA | 3.7 mm/year |
| Baltimore, MD | 5.5 mm/year |
| Norfolk, VA | 7.1 mm/year |
| Wilmington, NC | 4.2 mm/year |
| Charleston, SC | 8.8 mm/year |
Table showing maximum land subsidence rates measured in major East Coast cities from 2007-2022 as per the PNAS study.
The lead author of the research emphasized that this sinking represents an “existential threat” to these regions, exacerbating risks posed by climate change-driven sea level rise:
“This is an existential threat for these coastal regions…With global sea-levels projected to rise conservatively between 1-2m over the next century, accelerated subsidence represents catastrophic risk for exposed infrastructure and vulnerable communities across large swaths of the East Coast.” said Dr. Robert Young, Director of the Resilient Coastal Cities Lab at Virginia Tech.
Critical Infrastructure and Military Bases At Risk
The regions with detected subsidence contain vast networks of critical infrastructure supporting major metropolitan populations and economic activity, along with key national security sites.
Major international airports such as Boston’s Logan International are built on reclaimed land, while vital transit systems in cities like New York and Washington D.C. largely reside at or below current sea level. Interconnected services including transportation, power distribution, fresh water supply, and wastewater management face increasing vulnerability to tidal, storm surge and permanent inundation.
In addition to civilian infrastructure, crucial naval facilities and military installations are concentrated in subsidence hotspots identified along the Eastern Seaboard. This includes the world’s largest naval base in Norfolk, VA in addition to various shipyards, air stations, communications hubs, and strategic command centers – all vital to US defense readiness.
“Accelerated land subsidence represents a grave and unpredictable threat for exposed military facilities. Considering vast networks of underground infrastructure intrinsic to these sites, complex contingencies are urgently needed to maintain continuity of operations as land continues to sink and the sea rises around them.” said Pentagon spokespersonRear Adm. Charles W. Rock.
Triggers and Impacts of Accelerating Subsidence
While the processes driving contemporary land subsidence are complex, contributing factors likely include long term geological processes, extensive groundwater extraction, plus soil compression from urbanization. Regions built on loose sediment are prone to settling over time, with this consolidation accelerated by heavy building density characteristic of coastal cities.
Removing groundwater for municipal and industrial uses also results in subsurface voids leading to sinking surface elevation. Though groundwater management reforms have reduced extraction-linked subsidence in some areas, lingering impacts remain while much uncertainty persists regarding the influence of climate change.
Consequences stemming from accelerated land sinkage are already emerging across subsiding coastal zones. Increased nuisance flooding disrupts transportation networks and inundates buildings even on sunny days. Storm surge events lift higher and penetrate further inland. Saltwater from tidal flooding and surging seas contaminates surface water bodies and infiltrates aquifers. Foundations crack and infrastructure gradually degrades from constant inundation.
As displayed in the table below, measured subsidence rates now exceed relative sea level rise projections for these regions under conservative emissions scenarios for the coming decades. This will force additional elevation losses beyond expected sea level impacts.
| City | Max Subsidence Rate | Relative SLR Rate |
|---|---|---|
| Boston, MA | 8.1 mm/year | 6.3 mm/year |
| New York City, NY | 10.2 mm/year | 7.1 mm/year |
| Norfolk, VA | 7.1 mm/year | 6.5 mm/year |
Table comparing maximum subsidence rates vs projected sea level rise rates in select East Coast cities
Calls for Urgent Action to Protect Coastal Cities
Publication of the troubling InSAR findings has amplified calls for accelerated adaptation efforts to counter worsening land subsidence across America’s East Coast. Coastal resilience experts argue the latest evidence demonstrates an urgent need to update flood infrastructure, increase elevations of critical assets, and potentially relocate vulnerable communities over the long term.
However meaningful progress will require substantial investment at a scale not yet seen.
“These sobering findings highlight the need for immediate and sustained action to defend coastal cities against the double threat of sinking lands and rising seas. But minimizing future risk requires unprecedented resources – likely trillions in spending when all is said and done. Until dedicated funding appears, exposed regions will remain perilously vulnerable.” said Dr. Astrid Caldas, Senior Climate Scientist at the Union of Concerned Scientists.
In the absence of such investment, insurers warn that accelerating subsidence could trigger skyrocketing premiums and coverage pullouts endangering coastal property markets, while municipalities caution of potential credit downgrades and infrastructure funding crises.
Accordingly advocacy groups are campaigning aggressively for significantly expanded governmental support. However major federal assistance packages face doubtful prospects given the current political climate.
Outlook: Increasing Flood Exposure and Cascading Impacts
With high density cities and infrastructure already strained by nuisance flooding, thelooming interaction of higher seas plus faster sinking lands represents an existential crisis for exposed coastal regions. Even under managed climate policy scenarios limiting future warming, adapting major metropolitan areas to regular tidal inundation will necessitate extraordinary efforts.
Yet the extensive subsidence mapped across nearly 1000 km of US Atlantic coastline demonstrates already locked-in elevation losses outside relative sea level rise projections. This subsidence ensures increased flood exposure regardless of emissions reductions, while locking cities into inevitable and growing threats.
Absent rapid mobilization behind unprecedented coastal defense infrastructure, experts warn the destabilizing impacts of chronic flooding could trigger cascading economic, social and political turmoil across sinking East Coast population centers before this century’s end. The wide scale progressive inundation of America’s urbanized shores may soon emerge as one of the most dangerous and disruptive climate impacts facing the nation.
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