Why Cities Sink: The Slow Disaster Beneath the World's Great Cities

We talk endlessly about rising seas. We talk far less about the stranger, faster half of the problem: that many of the world's great coastal cities are sinking — some of them dropping toward the water many times faster than the ocean is climbing to meet them. And the main reason is not climate change. It is that we are quietly pumping the ground out from under our own feet.

Jakarta, the sprawling capital of Indonesia and home to millions, has a problem so severe that the country is doing something almost unheard of: building an entirely new capital city hundreds of kilometres away and preparing to abandon the old one to the sea. The reason is not simply that the ocean is rising. It is that Jakarta itself is sinking — in some neighbourhoods by tens of centimetres a year — settling downward far faster than the water is coming up.

Jakarta is the most dramatic case, but it is very far from alone. From Venice to Mexico City to Bangkok, and even parts of New York and Houston, some of the most important cities on Earth are slowly descending into the ground. It is one of the most under-appreciated slow-motion disasters of our time, and the most surprising thing about it is the cause. We tend to assume that cities near the water are threatened by rising seas. For a great many of them, the bigger and faster threat is the land going down — and much of that sinking is something we are doing to ourselves.

The counterintuitive truth: sinking beats rising

Start with a fact that reframes the whole conversation. The global sea level is rising, driven by climate change, at a rate of roughly three to four millimetres a year — about a tenth of an inch. That is a serious long-term problem. But when scientists surveyed around a hundred of the world's coastal cities, they found that a third of them were sinking at more than a centimetre a year — several times faster than the sea is rising. In the worst-affected places, mostly in Asia, cities are subsiding ten to twenty times faster than the ocean is climbing.

This is a crucial shift in perspective. For these cities, the flood risk they face in the coming decades is dominated not by how fast the sea rises, but by how fast the land drops. The two effects add together into what scientists call "relative sea-level rise" — the change in sea level as experienced by that particular piece of ground — and where the ground is sinking fast, that relative rise can be many times the global average. Flood models that account only for the rising sea, and ignore the sinking land, dramatically underestimate the danger. The water is coming for these cities much sooner than the climate headlines alone would suggest, because the cities are travelling downward to meet it.

So why is the land sinking?

The ground is a sponge, and we are wringing it out

The single biggest cause of urban sinking is deceptively simple: we are pumping too much water out of the ground beneath our cities.

To understand why that makes the land sink, picture what lies underground. Beneath many cities are aquifers — layers of sediment, sand, and rock whose countless tiny pores are filled with water. That water is not just sitting there passively; it is under pressure, and it helps hold the sediment grains apart, providing structural support to the ground above, rather like the water in a firm, soaked sponge helps it keep its shape. Now start pumping that water out — to supply drinking water, industry, and agriculture for a booming population — faster than rain can refill it. As the water is removed, the pressure that held the pores open disappears, and the weight of all the earth above squeezes those empty pores shut. The sediment compacts. And as it compacts, the ground surface settles downward. Wring out the sponge, and it collapses.

This is why the fastest-sinking cities are so often rapidly growing megacities in places with soft, water-logged ground: enormous, thirsty populations draw ever more groundwater from the aquifers beneath them, and the land steadily deflates in response. The process is usually gradual and invisible, a matter of millimetres and centimetres a year — but over decades it adds up to metres, and it does not easily reverse.

Groundwater extraction is the leading cause, but not the only one. The sheer weight of a modern city — its dense concrete-and-steel towers pressing down on soft ground — can contribute to the sinking. Many vulnerable cities are built on naturally compressible ground to begin with: soft river deltas, reclaimed land, or old lakebeds. And natural geological processes play a part too. But again and again, when scientists look for the dominant driver, they find it is the removal of water from below.

Three cities, three warnings

The abstract process becomes vivid in the world's great sinking cities, each of which tells a slightly different version of the story.

Jakarta is the extreme. Much of the city relies on groundwater wells because piped water supply is limited, so millions of people and countless businesses have been drawing down the aquifers for decades. The result is the highest average rate of urban sinking in the world, with some districts having dropped by metres over the years and large parts of the city now lying below sea level, increasingly reliant on walls and pumps to hold back the sea. The sinking is so unmanageable that Indonesia has begun relocating its capital to a new, purpose-built city far away — an admission that parts of Jakarta may simply be losing the fight. There is, however, a hopeful footnote: after the government tightened restrictions on groundwater extraction, Jakarta's sinking rate in recent years slowed markedly compared with a few decades ago, showing that the trend can be reined in.

Mexico City is the inland cautionary tale, proof that you don't need to be near the sea to be destroyed by subsidence. Built on the site of a drained ancient lakebed, the city sits on soft clay, and it pumps huge volumes of groundwater to supply its vast population. As that clay compacts, parts of the city sink dramatically — historically by dozens of centimetres a year in the worst spots, with some areas having dropped by many metres over the past century. Because it is not coastal, Mexico City doesn't face the sea — but the uneven sinking cracks buildings, tears apart roads and pipelines, and warps historic structures, a slow structural catastrophe unfolding across the metropolis.

Venice is the ancient and famous one, sinking for centuries into the soft sediments of its lagoon under a combination of its own weight, past groundwater extraction, and the natural settling of the ground. Battered by ever more frequent floods, Venice has resorted to a vast system of mobile flood barriers to hold back the highest tides. It is the world's most storied sinking city, and a preview of the engineering lengths to which threatened cities may have to go.

And the list runs on: Bangkok on its marine clay, barely above sea level; delta cities across Asia like Dhaka, Ho Chi Minh City, and Manila; rapidly growing coastal cities in Africa such as Lagos; and, more slowly but measurably, cities on the eastern seaboard of the United States, from New York to Houston, sinking a millimetre or two a year from a mix of groundwater use, the weight of development, and geology. Subsidence is not an exotic problem confined to a few unlucky places. It is a widespread condition of the modern, thirsty, densely built city.

Why it matters more than it seems

The consequences of a sinking city go well beyond eventual flooding, though that is the headline danger. As the ground subsides — often unevenly, sinking faster in some spots than others — it stresses everything built on and in it. Foundations crack. Buried pipes rupture. Roads buckle, rail beds warp, and runways develop dangerous slopes. The infrastructure of a city is engineered on the assumption that the ground beneath it will stay put; when it doesn't, the damage is chronic, expensive, and everywhere at once. Subsidence has even been implicated as a contributing stress in catastrophic structural failures.

And then there is the water. For coastal cities, sinking land plus rising seas means more frequent and more destructive flooding, storm surges reaching further inland, and saltwater creeping into freshwater supplies and soil. Hundreds of millions of people live in low-lying coastal cities, and a great many of those cities are sinking. The combination of a subsiding land surface and a rising ocean is a genuine threat to the long-term habitability of some of the largest urban centres humanity has ever built.

The rare good news

Here, though, is where the story of sinking cities diverges from the story of climate change in an encouraging way. Rising seas are extraordinarily hard to stop, requiring the whole world to change how it powers itself. But subsidence — the sinking part of the problem — is much more directly within our control, because we largely cause it ourselves by pumping groundwater.

That means it can be slowed by doing the opposite: reducing how much water we draw from the ground. The most powerful proof comes from cities that have already done it. When authorities have cracked down on groundwater extraction and supplied water by other means, the sinking has dramatically slowed — Jakarta's rate has fallen sharply under new restrictions, and Bangkok managed to slow its once-alarming subsidence after introducing regulations. Tokyo, decades ago, essentially arrested its own severe sinking by curbing groundwater pumping. Subsidence, once it has happened, generally cannot be undone — the compacted ground does not spring back up. But its progress can be halted. The tools are known: manage and limit groundwater extraction, provide reliable piped water so people don't have to rely on wells, recharge depleted aquifers where possible, and build with the reality of soft ground in mind.

The lesson of the world's sinking cities is therefore a double one. It is a warning about a hidden, accelerating danger that most people don't even know is happening beneath the world's great metropolises — and a rare, genuinely hopeful reminder that this particular disaster, unlike so many others, is one we have the power to slow, if we choose to stop wringing out the ground we have built our cities upon.

Sources and further reading

• Studies of coastal-city subsidence (e.g., surveys of ~99–100 cities in Geophysical Research Letters and reporting via the World Economic Forum and National Geographic) finding a third sinking faster than sea-level rise, some 10–20 times faster.
• Explanations of the mechanism: groundwater extraction removing pore-water pressure and compacting aquifer sediments, plus the roles of building weight and soft/reclaimed/lakebed soils.
• Case studies: Jakarta's extreme subsidence and the relocation of Indonesia's capital to Nusantara; Mexico City's lakebed-clay sinking; Venice's lagoon subsidence and flood barriers; and subsidence in Bangkok, Asian delta cities, Lagos, and US cities.
• References on "relative sea-level rise" (subsidence plus sea-level rise), the resulting flood and infrastructure risks, and the underestimation of risk by sea-level-only models.
• Reporting on slowed subsidence following groundwater regulation in Jakarta, Bangkok, and Tokyo.