Sinking Cities

India’s megacities are rising ever higher but the ground beneath them is slipping away. Gleaming expressways, metro lines and glass towers project the image of a nation surging into the future. Yet new research suggests this ascent may rest on perilously unstable foundations. Beneath the concrete sprawl of Delhi, Chennai, Mumbai, Kolkata and Bengaluru, the earth itself is sinking and in some places, alarmingly fast.

A study published in Nature Sustainability by researchers from Virginia Polytechnic Institute and other universities estimates that nearly 900 square kilometres of land across these five cities are subsiding, exposing 1.9 million residents to the risk of the ground dropping more than four millimetres each year. Satellite data from 2015 to 2023 reveal that more than 2,400 buildings are already at high risk of structural damage, while another 23,500 could face severe harm over the next half century if the trend continues. Delhi, soon to overtake Tokyo as the world’s largest metropolis, is sinking by as much as 51 millimetres a year in some areas.

Land subsidence, caused when groundwater extraction or construction compresses the earth beneath, unfolds too slowly for the human eye to notice, but its impact can be devastating. In Delhi’s suburbs of Ghaziabad and Faridabad, and in Chennai’s Adyar floodplains, the ground is quite literally buckling. Such uneven descent can fracture foundations, rupture water mains and amplify the toll of floods and earthquakes. The researchers even observed that parts of Dwarka in Delhi are rising by more than 15 millimetres a year, creating new stresses in the surrounding terrain.

The principal culprit is chronic groundwater depletion. Indian cities, long plagued by erratic rainfall and patchy water infrastructure, have turned to aquifers to slake their thirst. In Delhi-NCR, half the water comes from underground; in Chennai, borewells run deep into fossil aquifers that take centuries to refill. When the water is pumped out, the soil compacts and sinks. The weight of buildings, roads and flyovers adds pressure, accelerating the descent.

This slow-motion crisis lays bare the contradictions of India’s urbanisation. For all their economic dynamism, its megacities are being built on geologically fragile ground. The National Capital Region sits on soft alluvium that compresses easily when drained; Mumbai’s reclaimed coastlines have disturbed natural drainage patterns; Chennai has paved over the wetlands that once absorbed monsoon floods.

Subsidence lowers city elevations, making floods deadlier and drainage systems obsolete. It imperils metros and flyovers that rely on level terrain. As always, it is the poor who are crowded into the most flood-prone neighbourhoods who will bear the brunt when disaster strikes.

To avert catastrophe, India must take its subterranean world as seriously as its skylines. Cities should meter extraction, price water rationally and invest in large-scale recharge through rainwater harvesting and restored wetlands.

The earth’s slow descent is a warning that modernity cannot defy geology. Unless policymakers confront what lies beneath their feet, India’s urban miracle could collapse under its own weight.