Sea level rise is swallowing Mid-Atlantic farmland faster than expected, study finds
Virginia Institute of Marine Science
image:
Aerial view of a tidal marsh winding between two farm fields on Maryland's Eastern Shore, with a white salt patch visible on the right-hand field and a line of trees marking a levee between the marsh and farmland.
view moreCredit: Grace Molino
Ghost forests, the cemetery-like groupings of dead trees killed by saltwater intrusion, have become haunting symbols of sea level rise overtaking land along the Mid-Atlantic coast. But a new study in Nature Sustainability led by William & Mary’s Batten School & VIMS points to even more dramatic land losses in the region’s coastal farmlands, where the rate of marsh encroachment is happening nearly twice as fast.
Using satellite data spanning decades as well as recent field measurements, the study’s authors found that between 1984 and 2022 approximately 25,000 acres of farmland was lost to sea level rise in the Chesapeake and Delaware Bay watersheds, despite preventative measures taken by local farmers.
“There's this assumption that we'll never let sea level rise consume farmland, that people will protect valuable land. And it's just wrong,” said Matt Kirwan, co-author and professor of marine science at the Batten School of Coastal & Marine Sciences & VIMS. “We found lots of examples where small levees were built at the edges of fields to prevent saltwater intrusion, but they only slowed down the loss. They couldn’t stop it.”
Measuring marsh encroachment
As sea levels continue to rise due to human-driven climate change, saltwater creeps farther inland through groundwater, tidal creeks and storm surges. This process, known as saltwater intrusion, gradually kills freshwater plants and replaces them with salt-tolerant marsh grasses. Scientists track this transformation by measuring how the boundary between dry land and marsh shifts over time, a metric known as retreat.
Rather than measuring only how far inland the marsh boundary moved, which can depend on how flat or steep the land is, the authors tracked the elevation of the boundary as well. This approach accounts for differences in terrain and allows for a more direct comparison of marsh encroachment between farmland and forest.
The mid-Atlantic coast experiences sea level rise at roughly double the global average, making it both a hotspot for these changes and an ideal location to study them.
The study shows that marsh encroachment can be up to 7 times more frequent on agricultural land compared to forestland in the mid-Atlantic and that, regionally, agricultural land appears to have accelerated the impacts of saltwater intrusion.
“We hypothesized, and most people would intuitively expect, that marshes would migrate slower into farmland, that forests are more vulnerable than farmland. But we found the opposite,” Kirwan said. “On farmland, it’s much more subtle. It’s a row of crops at the edge of the field that’s brown instead of green, but it still adds up to thousands of acres of lost agricultural production.”
Why coastal farmlands are vulnerable
The study references an assumption that coastal farmland’s economic value incentivizes flood mitigation strategies to protect against sea level rise. In point of fact, mid-Atlantic farmers have built levees or earthen berms around their land to reduce inundation, along with other mechanisms like ditches.
However, because Virginia and Maryland made tidal wetlands protected ecosystems in the 1970s, few structural interventions have been built since then, raising doubts about whether coastal farmlands are as protected as presumed.
“Some of the berms are still being used and maintained, but a lot of them have been abandoned and are now surrounded by marsh,” said the study’s lead author and Batten School Ph.D. graduate Grace Molino ’25.
To conduct field surveys for the study, Molino visited six farm sites on the Eastern Shore along with co-author and former Batten School & VIMS student intern Grace Levins. They found that levees and other structural interventions did mitigate saltwater intrusion, bringing the vertical retreat rate in line with that of forests in the same area.
While these individual efforts did reduce marsh encroachment locally, the study found that regionally farmland was still more vulnerable to saltwater intrusion than forests. New construction is limited because of complicated permitting requirements, and the ones that are maintained cannot fully prevent land conversion to marsh. Additionally, crops are biologically less resilient than trees.
“It’s not that farmland is flat and therefore it retreats faster,” Kirwan said. “Trees have lifespans of hundreds of years. It can take decades to kill a tree. Agricultural crops have lifespans of less than a year.”
The overlooked impact of farmland on coastal resilience
Discussions around the impact of human development on coastal habitats have traditionally been focused on urban flood prevention methods like hardened shorelines and seawalls, which have been shown to prevent wetlands from migrating inland as seas rise. And yet, less than 15% of coastal watersheds in the United States are heavily developed. The vast majority of the nation's coastline is rural, and the human footprint on those landscapes has been largely overlooked.
“It's really underappreciated how large human impacts can be even in rural areas where you don't have the big beach houses, you don't have the big seawalls,” Kirwan said. “Everything's more subtle, but they're still having a big impact."
Rural communities are often not included in conversations about future flood infrastructure or coastal adaptation. The study argues that a paradigm shift is needed to understand the responses of these areas and the people who live in them.
Investigating these rural responses to marsh encroachment can be difficult. Researchers typically work on public land, where there is little barrier to entry. To access privately-owned farmland, Molino had to make old-fashioned cold calls and knock on doors. The effort was well worth it, she said.
“The landowners there have this unbelievable wealth of knowledge,” Molino said. “Most of them have lived on the land for several generations and know a lot about the neighboring properties and how things have changed.”
At one site in Maryland, a landowner who uses the property as a weekend hunting retreat during waterfowl season gave Molino a tour of two massive impoundment structures he had built on fields that were too salty to farm. One had been partially funded through a U.S. Department of Agriculture program that pays landowners to create wildlife habitat.
Molino said she was struck by how this landowner had independently adapted to saltwater intrusion by completely changing his land use, and that a federal program existed to support that decision.
“Individual landowner decisions have such a strong influence on the changes that we're seeing on the coast,” Molino said. “It's so important to actually get out into the field and talk with them and understand what's driving these decisions.”
Marshes are also under threat from sea level rise. If they can’t build soil fast enough to keep pace with rising tides, they must move to higher ground. So what may be bad for farmers in terms of land loss can at the same time be good for marshes, because agricultural land represents a new and faster pathway for them to migrate inland, potentially bolstering coastal resilience overall. But that comes directly at the expense of farmers’ livelihoods.
Molino believes that science can help figure out a solution for all. She cited the mission of the Batten School & VIMS to provide solutions-based science and how these farmers are exactly the kind of people she hopes science can serve.
In carrying out this study, science already has benefited these landowners. During one field visit, a landowner asked Molino to let him know if she found any breaches in his levees so he could plug them. When she got back to the lab, she called him and gave him the breaches’ exact GPS coordinates.
Journal
Nature Sustainability
Article Title
Sea-level-driven land conversion amplified by coastal agriculture
Article Publication Date
18-May-2026
Sea levels rising dramatically in some areas due to land subsidence
Weight of cities and declining groundwater levels worsen climate change impacts
- Land subsidence intensifies flood risks in coastal cities
- Groundwater extraction, oil and gas production, and heavy buildings drive sinking
- Groundwater management offers an effective countermeasure
Densely populated coastal regions in many parts of the world are particularly vulnerable to flooding. The sinking of land masses exacerbates the impacts of rising sea levels in these areas. This is shown by researchers from the Technical University of Munich (TUM) and Tulane University.
Global sea‑level rise is one of the greatest challenges of climate change: more than half a billion people live in low‑lying coastal zones. A research team from the German Geodetic Research Institute at TUM (DGFI‑TUM) and Tulane University in New Orleans shows in a study published in Nature Communications that people in densely populated coastal regions experience a relative sea-level rise of about 6 millimeters per year on average. This is roughly three times the coastline-weighted global mean of 2.1 millimeters per year, which describes the average relative rise measured worldwide along coastlines. Even when compared with the climate-driven absolute sea-level rise of around 3.15 millimeters per year, the value is still nearly twice as high. This amplified rise is caused by sinking land, a process known as subsidence.
Key drivers of land subsidence: groundwater extraction, resource use, ice loss, and tectonics
According to the researchers, the exact causes of subsidence cannot always be clearly identified in every case. However, among the most important and consequential factors are intensive groundwater extraction, oil and gas production, the compaction of young sediments in delta regions, as well as structural loads in rapidly growing cities. In addition, long-term geological processes such as tectonics and post-glacial adjustments also play a role.
“If we want to understand sea‑level rise along coastlines and respond effectively, we must not only observe the ocean but also the land itself. Especially in densely populated coastal regions, human activities cause the land to subside more strongly – often due to excessive extraction of water and resources that previously stabilized the subsurface. The sheer weight of cities, along with long-term geological processes, can further intensify this subsidence. In doing so, we significantly amplify the effects of climate‑driven sea‑level rise,” says Dr. Julius Oelsmann, lead author of the study and researcher at DGFI‑TUM.
Subsidence of Up to 42 Millimeters per Year
Countries with the highest relative sea-level rise include Thailand, Bangladesh, Nigeria, Egypt, China, and Indonesia, where population-weighted coastal averages of around 7 to 10 millimeters per year were calculated. The United States, the Netherlands, and Italy also show elevated values of about 4 to 5 millimeters per year.
Prominent subsidence hot spots include Jakarta (–13.7 mm/year), Tianjin (–13.5 mm/year), Bangkok (–8.5 mm/year), Lagos (–6.7 mm/year), and Alexandria (–4 mm/year). The extent of subsidence can vary greatly within individual cities: In Jakarta, some areas reach rates of up to –42 millimeters per year, while other parts of the city simultaneously show uplift.
Conversely, in some regions geological uplift leads to a relative decrease in sea level along coastlines, as seen in Sweden and Finland. There, the land continues to rise as a result of post-glacial rebound following the last Ice Age – and does so faster than sea levels are increasing.
Groundwater Management as a Countermeasure
“In many large coastal cities, groundwater extraction is a major driver of land subsidence. This means that local political and water‑management decisions can make a significant difference. Improved groundwater management, stricter regulation of withdrawals, or targeted recharge of aquifers can at least slow subsidence rates and, in some cases, largely halt them,” says Florian Seitz, Professor of Geodetic Geodynamics and Director of the German Geodetic Research Institute at TUM (DGFI‑TUM).
Successful examples include Tokyo and the metropolitan region of Houston, Texas. In Tokyo, subsidence rates once exceeded 10 centimeters per year, reaching peaks of around 24 centimeters per year in particularly affected areas. Through government intervention and the introduction of alternative water supplies, these rates were significantly reduced.
Similarly, in the Harris–Galveston region in Texas, intensive groundwater extraction was the main driver of subsidence. In response, the Harris-Galveston Subsidence District was established in 1975 to regulate groundwater withdrawal, promote alternative water sources, and support water conservation measures.
Journal
Nature Communications
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Subsidence more than doubles sea-level rise today along densely populated coasts
Article Publication Date
16-May-2026
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