In 1977, a photo was taken of hydrologist Dr. Joseph F. Poland standing next to a utility pole in California’s San Joaquin Valley. Signs on the pole indicate where the ground level was in a given year: At the top, one reads 1925; further down, 1955; at his feet, 1977. The ground had sunk almost 30 feet in about 50 years as a result of groundwater pumping. One would think the image would have become a wake-up call to the dangers of land subsidence. It was not.
A recent study in Nature Communications found that cities along the U.S. East Coast—home to roughly 118 million people—are sinking at a rate of roughly 0.12 inches a year. Across the nation, more than 17,000 square miles in 45 states are sinking. The situation is even worse in some places around the globe.
Mexico City, home to 21 million people, has sunk more than 32 feet in the last 60 years. Areas of Jakarta, Indonesia, population 11.2 million, have sunk 8.2 feet in the last 10 years and continue to sink almost 6 inches per year—a dilemma that has ultimately forced the Indonesian government’s decision to build a new capital city more than 1,200 miles away.
In its most basic definition, land subsidence happens when conditions change below ground. The changes can be natural, including soil settling, permafrost melting, and organic material such as peat compacting over time. Others are human-induced: the weight of buildings compacting soil, underground mining, oil extraction, and fracking. Then there’s groundwater extraction. As a recent headline in The New York Times states, “America Is Using Up Its Groundwater Like There’s No Tomorrow.” And that’s a problem.
“Land subsidence is greatly enhanced by groundwater pumping,” says Paul Chinowsky, director of Resilient Analytics, a consultancy that advises engineering firms on climate issues. “We are pumping more than is being restored into our underground aquifers.”
Overextraction of groundwater is responsible for more than 80 percent of known land subsidence occurrences in the U.S., according to the U.S. Geological Survey. As populations grow and groundwater extraction continues, land subsidence will only get worse—because once land sinks, it doesn’t rise again.
“Damages due to floods, earthquakes, or landslides are large and evident but can be resolved over time,” says Professor Pietro Teatini, of the department of Civil, Environmental, and Architectural Engineering at the University of Padova in Italy, and chair of the UNESCO Land Subsidence International Initiative. “The loss of elevation due to land subsidence is more difficult to notice, but it is permanent. Returning to the original condition is impossible.”
He explains that the reason land subsidence is irreversible is because soil doesn’t act like a sponge once it compacts. Adding water may prevent soil from compacting more, but it will never return to its original state. “Land subsidence is largely unrecoverable,” Teatini says, “because soil is more compressible when its pore pressure reduces due to groundwater pumping than when groundwater pressure recovers.”
Land subsidence often occurs slowly, which is one of the reasons cities neglect it. “Cities don’t think about how that small number impacts other events, but land subsidence essentially amplifies everything,” Chinowsky says.
Amplification comes in the form of relative sea level rise—the combined impact of sinking land and rising seas. In areas north of Tampa Bay, Florida, groundwater pumping has caused land to sink up to 0.24 inches per year, which will lower ground levels nearly 6.5 inches by 2050 if the rate of subsidence persists. Add the Florida Climate Center’s prediction that sea levels will rise 10 inches to 12 inches during the same period, and parts of Tampa Bay could face a relative sea level rise of 16.5 inches to 18.5 inches by 2050. This would put the city on track to be partially underwater by 2100.
“We’ve got to work with the hazards and not against the hazards. We have to look at everything from a risk perspective. That is going to require changing our design process and our thought process.”
PAUL CHINOWSKYDIRECTOR, RESILIENT ANALYTICS
The danger isn’t only to coastal areas. Depleting groundwater further inland can cause ground in one area to sink while a neighboring patch holds firm. When that happens, land fissures appear. Sinking land can also magnify flooding problems along major rivers and inland bodies of water. When land subsidence occurs, it tends to do so on an angle, Chinowsky says. So, during a storm surge, angled land channels water due to subsidence, essentially creating a path for that storm surge to quickly move inland.
Land subsidence can’t be reversed, but it can be stabilized. Managed aquifer recharge is one process, which essentially involves pumping water back into aquifers to stabilize ground levels. The city of Norfolk, Virginia, is hoping it will be a solution.
Areas of Norfolk are sinking more than 0.14 inches per year— twice the rate that its waters are rising. Its Sustainable Water Initiative for Tomorrow (SWIFT) is an aquifer recharge project to replenish the Potomac aquifer, eastern Virginia’s primary groundwater supply. SWIFT will pump purified water back into underground aquifers to increase groundwater stores for future consumption—and hopefully slow and stabilize land subsidence.
With increasing storm surges and rainfall, the question arises: Instead of propping up sunken land, could cities get ahead of the problem by using stormwater to naturally replenish groundwater resources? Unfortunately, most cities have pushed themselves into a corner. Stormwater infrastructure is designed to speed water away from populated areas as quickly as possible, preventing it from being able to seep back into the ground to recharge groundwater stores.
Chinowsky says cities should consider how to best utilize rainwater to recharge their aquifers naturally. “We need to think about not pushing water away, but about where the water actually needs to go,” he says. “It’s not just rethinking how we create things, but rethinking land use so we can allow water to recharge aquifers. And that really goes against everything that we’ve been doing for 100 years.”
The city of Charleston, South Carolina, has been rethinking how to protect itself from sinking land and rising seas. As Dale Morris, chief resilience officer and director of emergency management for the city of Charleston, says, “Charleston is the canary in the coal mine. We have every type of flood risk known.”
About 50 percent of the Charleston peninsula is built on filled and reclaimed land. Those and some other areas of the city are now sinking 0.12 inches to 0.16 inches a year, says Morris, due to the natural/geologic processes of soil compacting. That equates to an inch of land subsiding every six years or so. If sea levels rise an inch every two years, which is what the city is planning for, it will have to deal with about four inches of relative sea level rise every six years.
Since 2010, Charleston’s population has increased by over 34 percent. “All that development, done unwisely, can exacerbate problems,” Morris says. To protect against future threats, he says developers now must follow Charleston’s stormwater design standards “to make sure they’re storing more stormwater, managing more stormwater in a better way, and are thinking of the outflow conditions with a certain amount of sea level rise.”
The city has also invested $200 million in a deep-level tunnel project to cope with increased stormwater in lower land elevations.
Another concern is shallow groundwater flooding. “With the hydrostatic pressure from the Atlantic Ocean and our rivers, the shallow groundwater is going to rise up as the seas rise,” says Morris. “And since we’re so flat, we are starting to see that—and we’re starting to worry.”
Charleston is anticipating 14 inches of sea level rise by 2050. “That informs a lot of our planning,” Morris says. “It’s not protection or retreat. It’s developing the right way and helping the areas that are vulnerable now and going to get more vulnerable because of the changing climate.”
As cities sink and sea levels rise, so does the risk of climate gentrification. Scientific American reports that over 1 million people in Miami alone may be displaced due to climate change by 2100. More than half of Miami-Dade County will feel pressure to relocate—and those who can’t afford to do so will have fewer options.
Wealthy locals and retirees have always preferred waterfront homes in Miami Beach. Yet with the combined threat of sea level rise and areas sinking up to 0.12 inches a year, residents and developers are seeking higher ground. Sitting at 10 feet above sea level, the immigrant neighborhood of Little Haiti has become prime real estate.
Pamela Yonkin, sustainability and resiliency director for HDR, explains, “The amount of land we can build on is going to decrease on the coasts. Places that are higher up, like Miami’s Little Haiti, are going to become more desirable. An increase in demand, combined with a fixed or diminishing supply of land, often leads to increased prices on existing real estate.”
“There are a lot of ways to build infrastructure to protect against climate impacts, and a community’s preference is an important consideration when choosing which course to take.”
PAMELA YONKINSUSTAINABILITY AND RESILIENCY DIRECTORHDR
It’s something Little Haiti is already experiencing, forcing longtime residents out of the neighborhood, according to The New York Times. In April 2012, the average home value in Little Haiti was $58,403; in April 2023, it was $482,557. Similar situations are occurring in other areas of Miami, such as Liberty City (8.5 feet above sea level) and West Coconut Grove (10 feet above sea level).
Yonkin encourages engineering firms to think about how a potential infrastructure project will affect all members of a community during the early planning stages. That way, they can seek input from the public and weigh the risks and benefits of different infrastructure alternatives before key decisions are made.
“Gentrification is not a new issue—it is just new in this context—and some of the tools we use are relevant,” she says. “We encourage our clients to consider things like mixed income development, inclusionary zoning policies, and incentives to control displacement.”
To maximize the potential of the existing land while also contributing to the public well-being, Morris advocates for infrastructure with multiple functional benefits.
“Engineering communities are really good at developing single-purpose infrastructure, but they have to do more than that when they look at land use and green infrastructure,” he says. “It isn’t a neat and tidy box of ‘Go solve this engineering problem.’ It’s people, it’s place, it’s urban fabric, it’s greenery, it’s stormwater ponds that are attractive—it’s all those things.”
Morris cites Charleston’s Low Battery Renovation project as an example. The original Low Battery was a seawall installed 100 years ago that was showing its age and inadequacy as tides began overwhelming it. So the city did a complete overhaul of the site. It raised the seawall, rebuilt the street next to it, added a wider walking path and parklets, and made all of it Americans with Disabilities Act-accessible.
“We have a multifunctional tidal management structure to help us deal with storm surges,” Morris says. “People walk it all the time, people fish off it and are just delighted with how it looks and how it functions. It’s a combination of really good engineering, good urban design, good transportation—all put together.”
Multipurpose infrastructure that puts the community “front and center” is essential. “There are a lot of ways to build infrastructure to protect against climate impacts, and a community’s preference is an important consideration when choosing which course to take,” Yonkin says.
To effectively address sinking land and rising seas, Chinowsky believes engineers will need to reconsider the relationship between the built environment and nature. “The 1970s, when a lot of infrastructure and urban expansion took place, was a time when engineering had a perspective of man over nature—anything that was there, we could conquer it,” he says. “If this mentality continues, we’re going to lose in the long run.”
“The loss of elevation due to land subsidence is more difficult to notice, but it is permanent. Returning to the original condition is impossible.”
PIETRO TEATINIPROFESSOR, UNIVERSITY OF PADOVALAND SUBSIDENCE INTERNATIONAL INITIATIVE CHAIRUNESCO
Yonkin agrees, particularly when that approach comes with costs of constant upkeep. “A roadway or water system built in a vulnerable area that needs to be repaired over and over again is not a good use of public funds, even if from an engineering perspective we can fix it,” she says.
It’s time to think differently, says Chinowsky. “We’ve got to work with the hazards and not against the hazards. We have to look at everything from a risk perspective,” he says. “That is going to require changing our design process and our thought process. We have to get out of this mindset that design is looking at books and looking at tables and following the standards.”
That is because the standards often set requirements based on historical climate data, which may no longer be relevant given the rapid pace of climate change. Designing to the standards may meet today’s requirements, but firms must also prepare for what’s ahead. “Is what we’re designing today meeting both the requirements of today and of the future?” Chinowsky says. “Are you meeting the obligation of that infrastructure in 20 or 30 years?”
As the climate and the land continue to change, engineers must rise to the occasion and work to ensure a sustainable future.
Scott Burnham is a writer based in Waltham, Massachusetts. He has written for Architizer, Metropolis, Skanska, and The Guardian.
Tokyo’s response to land subsidence shows how rethinking the role of rain can stabilize a sinking city’s future.
Starting around 1910, Tokyo’s Kōtō City district began drawing heavily from the city’s groundwater to support an exploding population and burgeoning industrial activities. Excessive pumping in Kōtō City and other parts of Tokyo caused land to sink roughly 15 feet over the course of 50 years, with some areas losing about 4 inches each year; the peak year was in 1968, when some areas lost up to 9.5 inches of ground elevation.
In the early 1970s, the Tokyo Metropolitan Government (TMG) became serious about tackling land subsidence. It implemented a range of regulations to reduce groundwater pumping and increase the permeation of rainwater infiltration to recharge groundwater stores in green areas and farmland. Shortly after the regulations took hold, land subsidence in the city leveled off.
The city’s grand pivot was born from a simple principle: Instead of barricading against rain, let the rain in as nature intended. TMG assessed that the majority of Tokyo was covered by impermeable surfaces and infrastructure—such as buildings, roads, concrete viaducts, and drainage systems. Yet beneath the city’s surface was a layer of highly permeable red soil, which historically gave the area abundant groundwater resources. TMG realized that a means of recharging groundwater stores was already in place—it just needed to let the rain reach the soil, and nature would take over.
So TMG established extensive guidelines for rainwater permeation: Any new groundwater pumping facilities must install rainwater infiltration facilities to ensure an equilibrium between the volume of water pumped and that which is permeated back through the soil. Plans were even made for expanding water-permeable pavement and rainwater infiltration measures in the city’s general flood control and urban development project.
As a result, areas that once experienced nearly 10 inches of subsidence each year now register at about 0.4 inches annually.
“By working with rain instead of guarding against it, Tokyo not only reduced its risk of land subsidence, it restored nature’s self-regulating system,” says Professor Pietro Teatini, of the department of Civil, Environmental, and Architectural Engineering at the University of Padova in Italy, and chair of the UNESCO Land Subsidence International Initiative.
“It’s not protection or retreat. It’s developing the right way and helping the areas that are vulnerable now and going to get more vulnerable because of the changing climate.”
DALE MORRISCHIEF RESILIENCE OFFICERDIRECTOR OF EMERGENCY MANAGEMENTCITY OF CHARLESTON