Issues related to groundwater
Issues of over-exploitation:
- 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 one-fourth of the global total.
- India, Pakistan, and Bangladesh are, respectively, the first, fourth, and sixth largest users of groundwater globally. India pumps more than the US and China combined — the second and third-largest users, respectively.
- Drop in water table:
- 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.
- Among the major states, Tamil Nadu had 87% of wells showing a dip in groundwater followed by Punjab (85%).
- 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.
- 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.
- Land subsidence:
- Land subsidence due to groundwater pumping is a problem threatening several Asian cities.
- Experts now predict that Indian cities, too, are likely to face land subsidence if over-exploitation of groundwater continues unchecked.
- Environment & safety:
- Land subsidence and ground rupture can significantly affect the environment and safety of the people.
- Experts said that 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 with sinking rates of 10-20mm/year. Ground rupture has been observed in the Indian hinterland, for example in Uttar Pradesh, adds Teatini.
- 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.
- Example of Uranium contamination:
- Findings: Many parts of Rajasthan may have high uranium levels in their groundwater, according to a study by researchers at the Duke University in North Carolina, United States, and the Central Groundwater Board of India.
- Source: The main source of uranium contamination was “natural,” but human factors such as groundwater table decline and nitrate pollution could be worsening the problem.
- Cases of land subsidence in western countries and in Asia show that the only check against it is the shutdown of pumping wells and supply of potable water through alternative sources.
- Total static groundwater available in India is about 10,812 bcm.
- The average groundwater recharge rate of India’s river basins is about 260m³/day.
- Estimates suggest that India has about 433 bcm of groundwater which is replenished annually through rain and river drainage. Out of that about 398 bcm is utilizable.
- As per estimates India is pumping out some 190 BCM/yr of underground water a year. Nature is refilling only 120 BCM. So, there is shortfall of 70 BCM per year
Section : Environment & Ecology