It is the backbone of India’s drinking water and irrigation supply systems, but overexploitation of groundwater is a threat to not only our food security but also the stability of the land, says Radheshyam Jadhav in the third of the series for TOI’s Water Positive campaign.
India is standing on a slippery slope when it comes to our use of groundwater. Literally. Because in overexploiting this resource, we are risking more than just our ability to meet our future water needs. Groundwater overusethreatens the stability of the land.
Land subsidence due to groundwater pumping is a problem threatening several Asian cities. Beijing, Jakarta, Dhaka, Bangkok, Ho Chi Minh City, Shanghai in the recent past, and Tokyo in the 1960s-1970s have all faced the problem. Experts now
predict that Indian cities, too, are likely to face land subsidence if overexploitation of groundwater continues unchecked.
Land subsidence and ground rupture can significantly affect the environment and safety of the people. Cases of land subsidence in western countries (Venice and Ravenna in Italy, Houston in US) and in Asia show that the only check against it is the shutdown of pumping wells and supply of potable water through alternative sources.
According to Italy-based scientist Pietro Teatini, land subsidence can be significant in coastal zones along the Bay of Bengal, such as the deltaic regions of the Mahanadi, Godavari, Krishna and Cauvery rivers. Kolkata is already suffering, he says, with sinking rates of 10-20mm/year. Ground rupture has been observed in the Indian hinterland, for example in Uttar Pradesh, adds Teatini.
Meanwhile, as Indian cities continue to drill deep for water, more than 60% of wells analysed by the Central Ground Water Board (CGWB) had levels lower than the decadal average (2007-2016) and about a sixth 17.5%) had levels 2 metres or more below the average. These 2017 pre-monsoon numbers are a cause for concern considering that 90% of rural domestic water use is based on groundwater and 70% of water for agriculture comes from aquifers.
Of the 14,465 wells CGWB surveyed, water levels were down in 8,785. Among the major states, Tamil Nadu had 87% of wells showing a dip in groundwater followed by Punjab (85%). Just 38% of the wells across states showed a rise in water levels over the decadal average. Even among these, the overwhelming majority are less than 2 metres above the average. A recent report warns of a major crisis due to over-extraction and groundwater contamination covering nearly 60% of all districts. It says there is mounting evidence to suggest that 50% of urban water usage comes from groundwater.
The South Asia Ground Water Forum says the region is the largest user of groundwater, accounting for nearly 50% of the total groundwater pumped for irrigation globally. Groundwater abstracted in the Indo-Gangetic basin is about onefourth of the global total.
Radheshyam Jadhav| TNN | Jun 9, 2018, 08:14 IST
