By Shatakshi Gawade
Imagine a stacked pile of papers. Every time a single sheet is pulled out from the middle, the top sinks, imperceptibly. More sheets would of course lead to more sinking. In our case, the stack is the Earth’s crust, the removed sheet is extracted groundwater, pumped from deep borewells, and the sinking top layer is the surface we are on. Such a sinking surface – land subsidence – is the alarming reality in several parts of the country as groundwater extraction continues unabated.
Groundwater is stored under the surface of the Earth in cracks and pores of rock and soil in structures called aquifers. An aquifer is a water-bearing rock that allows the groundwater to flow into wells and springs, which may flow into streams or lakes. Water seeping down into the soil recharges these aquifers. But the rate of recharge is different according to the type of rock, which is why the well may run dry if the extraction is higher than recharge, or land may subside.
By some estimates, human activities are responsible for 77 per cent of the ground subsidence across the world, of which 60 per cent is attributed to groundwater extraction. With a fourth of the planet’s groundwater being withdrawn in the country, India is the largest user of the underground resource.
Groundwater provides 48 per cent of the water supply in Indian cities. U.S.A.’s National Aeronautics and Space Administration (NASA) has recorded that in just the last decade, the groundwater in north India has decreased by 108 billion cubic metres. Such unabated, often unregulated, extraction of groundwater is causing land subsidence and recent research suggests is even tilting the Earth’s axis.
Researcher Shagun Garg found that land was subsiding in Kapashera, 10 km. from Delhi’s airport, at the rate of 17 cm. per year. He also observed sinking land in other parts of Delhi NCR. This corresponds with the over four metre decline in groundwater in some pockets of Delhi, in wells monitored by the Central Ground Water Board (CGWB) in November 2020 compared to the decadal average (2010-2019). CGWB has recorded a decline of about 33 per cent of groundwater in wells across India by upto two metres. A decline of over four metres has been observed in Dehradun, Ghaziabad, Indore, Allahabad, Kanpur, Lucknow, Jaipur, Vijayawada, Chennai, Coimbatore and Madurai.
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Groundwater being pumped at a farm. Human activities are responsible for 77 per cent of the global ground subsidence, of which 60 per cent is attributed to groundwater extraction. Photo: Suraj Mondal.
The other causes for groundwater loss are changes in the landscape on account of infrastructure such as building basements, tunnels and metros, which disturb aquifers and recharge and discharge zones. Land subsidence causes damage to structures, making buildings unsafe, damaging linear infrastructure such as roads and railways, causing changes in elevation of streams and canals, which may cause them to breach their banks, flooding, and mine inundation. All of these lead to economic losses, and unnecessary loss of human life. Researchers believe that reversing land subsidence is not possible. The only way to arrest this deadly phenomenon is to manage groundwater extraction, and plan infrastructure carefully in a way that does not damage aquifers.
The warmer colours in the map of north India show greater sensitivity to groundwater storage changes. NASA found that 109 cubic km. of groundwater disappeared here from 2002 to 2008, at an average of one metre every three years, proving that the current rate of groundwater extraction is not sustainable. Photo: Public Domain/NASA/Matt Rodell.
