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From New York City to Manila, some of the world’s largest and most vibrant coastal cities are battling a silent and monstrous challenge: sinking land. Known as land subsidence, this phenomenon exacerbates the effects of rising sea levels, threatening millions of people and the infrastructure that sustains their lives. But what is causing this slow and steady descent into crisis? And can anything be done to stop it? Click on the first slide to know more.
Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Around the globe, this is becoming an increasingly urgent issue.
In a study published in Nature Sustainability, researchers used satellite-based radar to measure the degree of relative land subsidence in 48 of the world's largest coastal cities. They found that nearly all of these cities are experiencing some degree of land subsidence. In 44 of them, certain areas are sinking at a much faster rate than the sea is rising.
The most effected cities include Tianjin (China), Ho Chi Minh City (Vietnam), Chittagong (Bangladesh), Yangon (Myanmar), Jakarta (Indonesia), Ahmedabad (India), Istanbul (Turkey), Houston (USA), Lagos (Nigeria), and Manila (Philippines).
In the densely populated northern part of Metropolitan Manila, Philippines, the cities of Navotas and Malabon's exposure to frequent flooding has led to significant changes, including the adaptation of the country's iconic jeepneys—elaborately decorated buses—now made from stainless steel to withstand corrosion from seawater.
Streets have been raised repeatedly over the years, with some now elevated higher than the entrances to people's homes. "They keep on putting the roads higher and higher, but I don’t know how they can sustain that," said Dr. Mahar Lagmay, executive director of the University of the University of the Philippines Resilience Institute to the BBC.
Places all around the world are falling victim to the “big sink.” The submerging of cities, also known as land subsidence, occurs when the ground loses its ability to support the weight above it. One of the primary causes is the over extraction of groundwater.
For example, Jakarta, the capital of Indonesia, is often called the fastest sinking city in the world. In some areas, the land drops by up to 25 centimeters each year due to excessive groundwater pumping.
As aquifers are depleted, the ground compresses, causing a gradual but significant drop in elevation. Experts predict that by 2050, about 95% of North Jakarta will be submerged.
With global warming, rising sea levels and sinking land, Egypt could lose one of its treasures: the city of Alexandria.
Its millions of inhabitants will have no choice but to become climate exiles. Already, hundreds of Alexandrians have had to leave apartments weakened by flooding.
Urban development plays a significant role. The weight of modern infrastructure, combined with inadequate planning and poorly regulated construction, exacerbates subsidence.
Coastal cities are particularly vulnerable, as they are often built on soft, unconsolidated soils that are more prone to compression.
Rising sea levels due to climate change compound the issue of sinking cities. As global temperatures increase, polar ice caps and glaciers melt, leading to higher ocean levels.
Coastal cities already grappling with subsidence find themselves doubly exposed. The combination of sinking land and rising seas accelerates the rate at which these cities are becoming uninhabitable.
The impact on urban populations is profound. Sinking cities face frequent flooding, which disrupts daily life and damages critical infrastructure.
Transportation networks, utilities, and housing all suffer, leading to economic losses and displacement. In Jakarta, for instance, entire neighborhoods are at risk of being submerged, forcing residents to relocate and leaving behind ghost towns.
Health risks also escalate in sinking cities. Floodwaters often carry pollutants, leading to outbreaks of waterborne diseases. Inhabitants, particularly those in low-income areas, face increased exposure to health hazards, with limited access to medical resources.
Venice, a historic city renowned for its canals, has become a symbol of the fight against subsidence and rising sea levels. Despite implementing measures like the MOSE flood barrier project, Venice continues to face challenges in protecting its cultural heritage.
MOSE (Modulo Sperimentale Elettromeccanico) is designed to protect Venice from flooding, which is one of the primary factors contributing to the city's sinking. The project works by deploying large gates that can be raised to seal off the Venetian Lagoon from the Adriatic Sea during high tides, known as "acqua alta."
When a high tide of 51 inches (130 cm) or more is predicted, the gates rise to block the flow of water into the lagoon, preventing the city from experiencing devastating floods. MOSE is Italy's biggest engineering project ever, and among the biggest in the world (according to How Stuff Works). The cost, initially estimated at US$1.35 billion (1.3 billion Euros), has risen to US$6.2 billion (6 billion Euros).
By controlling the water levels, MOSE aims to reduce the pressure of rising sea levels and extreme tides, which, over time, have contributed to Venice's gradual sinking. In addition to flood protection, the system helps preserve the city’s infrastructure, historical sites, and natural environment, which are all at risk due to rising waters.
New York is studying the MOSE project as a potential solution to protect the city from rising sea levels, but it faces a much larger challenge. To safeguard New York City, it would require 6 miles of barriers, with costs estimated between US$62 billion and $200 billion.
Building a sea wall around New York could have unintended consequences for surrounding areas such as Long Island, New Jersey, and Connecticut. As Justin Davidson explains in Curbed.com, "Water that hits an artificial wall doesn't just go away; it caroms off to somewhere else," potentially worsening flooding for neighboring regions.
In areas like New Orleans and Port Arthur, median property values are generally lower, indicating a higher concentration of lower-income residents. This economic disparity means that these communities are more vulnerable to face significant exposure to the impacts of land subsidence and sea level rise by 2050.
In Bangkok, land subsidence of up to two centimeters (0.78 inches) per year, coupled with rising sea levels, threatens its role as a hub for Southeast Asia. The Thai government is exploring large-scale infrastructure solutions, including constructing seawalls and relocating at risk communities.
To combat the sinking of cities, governments and urban planners must take urgent and coordinated action. Reducing groundwater extraction is a critical first step. Cities can invest in alternative water sources, such as desalination plants and rainwater harvesting systems, to reduce reliance on underground aquifers.
Sustainable urban planning is equally essential. Utilizing lighter construction materials and limiting high-rise developments in vulnerable areas can help mitigate the problem.
Restoration of natural ecosystems, such as mangroves and wetlands, also offers a buffer against rising sea levels while helping to stabilize the ground. Sinking cities are a stark reminder of the interconnected challenges of urbanization, climate change, and resource management.
While the issue is daunting, it is not insurmountable. As the world grapples with the twin challenges of rising seas and sinking lands, it becomes clear that the time for action is now.
Through proactive measures, collaboration, and investment in sustainable practices, we can ensure that the world's urban centers remain vibrant and resilient for generations to come.
Sources: (Yale) (CNN) (Science Focus) (Voronoi App) (Nature) (Engineering) (Ahead Of The Herd)
Coastal cities at risk of submersion
Earth's largest cities are descending into the sea
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From New York City to Manila, some of the world’s largest and most vibrant coastal cities are battling a silent and monstrous challenge: sinking land. Known as land subsidence, this phenomenon exacerbates the effects of rising sea levels, threatening millions of people and the infrastructure that sustains their lives. But what is causing this slow and steady descent into crisis? And can anything be done to stop it? Click on the first slide to know more.