India’s biggest cities are sinking - and it’s part of a worldwide trend

India’s biggest cities are facing a crisis that grows deeper every day. Beneath the crowded streets and high-rise buildings, the land itself is sinking.

Scientists from Virginia Tech have shown that this quiet descent is already weakening buildings and threatening millions of lives.

The study, published in the journal Nature Sustainability, turns the ground beneath India’s urban centers into a subject of urgent concern.

Why India’s cities are sinking

The researchers studied five megacities – New Delhi, Mumbai, Chennai, Kolkata, and Bengaluru – using satellite radar data from 2015 to 2023. They discovered that 878 square kilometers of land are sinking.

Nearly 1.9 million residents live in areas where the ground drops more than 4 millimeters every year. The reason is simple yet alarming: overuse of groundwater.

“When cities pump more water from aquifers than nature can replenish, the ground quite literally sinks,” said Susanna Werth, assistant professor of geosciences at Virginia Tech.

“Our study shows that this overexploitation of groundwater is directly linked to structural weakening in urban areas.”

As water is drawn out, the soil compresses. Empty spaces underground collapse, and the surface begins to sink. Monsoon changes have made this worse by reducing how much water seeps back into aquifers.

Satellite data also show a long-term decline in India’s total water reserves, a trend now visible from space.

Cities face uneven sinking

Each city tells a different story. Delhi’s land sinks because of compressed river sediments that have supported centuries of construction.

Some areas like Dwarka show slight recovery due to government rules limiting groundwater pumping and encouraging rainwater collection.

Chennai faces faster sinking, especially along the Adyar River and central neighborhoods like Valasaravakkam and Kodambakkam. Sandy and clay soils there compact easily.

Mumbai’s dense settlements, such as Dharavi, experience local sinking from unregulated borewells. Bengaluru’s hard rock base has slowed the process, though increased water extraction since 2022 signals growing danger.

The study also hints that the sheer weight of modern buildings might be pushing the ground further down. Skyscrapers, roads, and concrete layers together create a load the earth can no longer hold evenly.

Uneven ground weakens buildings

The problem isn’t just that the ground sinks – it sinks unevenly. This differential movement, called “differential settlement,” strains buildings from the base up.

Foundations bend, walls crack, and underground pipes break apart. Once a structure starts to shift, even slightly, the stress travels through every floor.

“The silent strain we see today could lead to tomorrow’s disasters if cities do not adapt their infrastructure and groundwater management policies,” said lead author Nitheshnirmal Sadhasivam.

This warning connects local problems to a larger pattern of neglect. Subsidence rarely acts alone – it teams up with weak materials, old construction, or floods to create catastrophe.

Satellites track sinking cities

To track the slow sinking, researchers turned to satellites. Using Interferometric Synthetic Aperture Radar (InSAR), they captured land movement across entire cities with millimeter accuracy.

Over 1,200 radar images built a clear picture of India’s urban ground shifting over time. The results showed how small, gradual changes can add up to large structural risks.

“Our research shows how satellite-based ground mapping techniques can reveal risks that are otherwise hidden until collapse occurs,” said Professor Manoochehr Shirzaei.

The study used a measure called “angular distortion” to calculate how much a building tilts or bends due to uneven land movement. More tilt means more damage.

About 2,406 buildings in Delhi, Mumbai, and Chennai already show high risk. If nothing changes, more than 23,000 buildings could face severe structural threats within 50 years.

Cities under growing pressure

Chennai tops the list for future damage, followed by Delhi and Mumbai. In some neighborhoods, foundations already strain under uneven soil pressure.

Once cracks appear, they rarely close. Water seeps in, corrosion spreads, and small faults grow into serious hazards. Even cities with lower current risk, like Bengaluru and Kolkata, cannot relax.

Uneven land movement can disrupt drainage and water lines, making floods worse and repairs harder.

Engineers and planners face a difficult reality: subsidence doesn’t announce itself. It happens quietly until the damage is visible, and by then, prevention is too late. Floods, earthquakes, and storms all amplify the stress that sinking soil begins.

Climate adds more strain

Changing rainfall, intense droughts, and rapid urban growth all feed the problem. When dry years force cities to dig deeper for water, the ground loses strength.

The researchers predict that as global water demand rises, many other cities will experience the same cycle of overuse and collapse. More than 150 urban regions worldwide already face measurable subsidence.

Climate change worsens the pattern. Wetter monsoons cause floods that erode weakened ground, while drier ones increase groundwater pumping.

The study shows that India’s challenge mirrors global struggles where land, water, and infrastructure compete for survival.

Tech helps sinking cities

The scientists propose turning satellite monitoring into a standard part of city planning. Regular InSAR scans can identify at-risk zones long before foundations fail.

Engineers could then reinforce vulnerable structures or redesign drainage systems. The same data can also guide policies for sustainable water extraction.

“Investing in adaptation now, through groundwater regulation, resilient design, and proactive monitoring, will save lives and resources in the long run,” said Shirzaei. His message points to prevention rather than repair.

Building smarter, not just higher

New building codes must include land movement data. Groundwater management should pair with construction planning so that cities don’t keep building on unstable ground.

Reviving local ponds, planting vegetation, and using artificial recharge wells could help stabilize soils. Satellite data can track whether such efforts work in real time.

India’s rapid urban expansion has come with invisible costs. Every skyscraper and highway adds pressure to the land below. Without better water control and long-term monitoring, cities risk turning their progress into collapse.

A quiet warning for the world

This is not just India’s problem. Cities across Asia, Africa, and the Americas depend on aquifers that are draining fast.

The same slow sinking seen in Delhi or Chennai could unfold anywhere water tables drop. The ground does not forgive imbalance – it simply adjusts downward.

The message from this study is clear: stability cannot be assumed. The land beneath us is changing, slowly but surely. Whether cities choose to act now or later will decide if that change ends in cracks or collapse.

The study is published in the journal Nature Sustainability.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–