How crucial is groundwater recharge in irrigation?

April 5, 2022, 1:48 PM IST

MG Chandrakanth in Economic Policy, Environment, India, TOI.

India is the largest pumper of groundwater in the world, pumping twice that of the USA and 6 times that of Western Europe, pumps around 75 acre inches per well from around 30 million irrigation wells. Around 70% of irrigation in India is from groundwater. It is crucial to appreciate the role of natural recharge of groundwater and how it influences pumping from an irrigation borewell. Thus recharge of groundwater is crucial for sustainable extraction. Hard rock areas of India form 65% of its geographical area where recharge from rainfall is hardly 10%. Therefore if farmer receives a rainfall of around 750 mm in a year, only 75 mm is the natural recharge and the rest drains away.

Volume of rainwater pumped in relation to recharge

On one acre of land which is 4000 square meters, rainfall of 750 mm per year implies as under: 750 mm of rainfall is 0.75 meter. On 4000 sq. meters, rainfall of 0.75 meter implies = 0.75M X 4000 Sq. M = 3000 cubic meters. Given 1 cubic meter is = 1000 litres of water, 3000 cubic meters = 3000000 litres of water. Since one gallon of water = 4.54 litres, 3000000 litres of water = 660793 gallons, which is equal to 29 acre inches or ha cms since 1 acre inch or 1 ha cm = 22611 gallons of water. Therefore 1 acre with 750 mm of rainfall is approximately equal to 29 acre inches of rainwater assuming modest evapo transpiration. Each irrigation of 5 cms for paddy is around 2 acre inches for one acre.

Unsustainable extraction of groundwater

Considering recharge to groundwater from rainfall of 10%, out of 29 acre inches only 2.9 acre inches will enter the aquifer. One irrigation well extracts around 100 acre inches of groundwater. On an average an irrigation well irrigates around 3 acres. Thus, for three acres, the total recharge is 2.9 acre inches X 3 acres = 8.7 acre inches or approximately 9 acre inches. Thus, by recharging 9 acre inches of water farmer is pumping out 100 acre inches of water per well on an average every year leaving a gap of approximately 90 acre inches to be recharged by other areas consciously or unconsciously. Thus extracting 100 acre inches from a well and recharging only 9 or 10 acre inches is over exploitation leading to massive failure of borewells forcing farmers to invest on drilling new wells continuously.

Awareness regarding groundwater extraction

Therefore it is crucial to educate farmers that they are withdrawing around 100 acre inches of groundwater from one irrigation well, is in fact extracting groundwater from at least another 30 acres of land, since each acre recharges only around 3 acre inches of water per year. Unless groundwater recharge programs are undertaken on a massive scale, groundwater wells will face premature, / initial failures. Studies in the Dept of Agricultural Economics, UAS Bangalore funded by the Ford Foundation since 1995 till 2005 indicate that (1) probability of well failure is around 0.4; (2) open wells/dug wells have virtually vanished due to the advent of deeper borewells over time (3) the amortized cost of groundwater per acre inch ranges from Rs. 300 to Rs. 400 without considering electricity cost (4) to lift one acre inch of groundwater, the electricity cost is around Rs. 100, which implies Rs. 10,000 per year per well for 100 acre inches (5) The total cost of groundwater inclusive of electricity ranges Rs. 400 to Rs. 500.

Implications of cultivating paddy and sugarcane using groundwater

Farmers and our Government, if they are really concerned about the precious and scarce groundwater should first think of the current crop pattern in well irrigation. For example, how ethical to cultivate paddy / sugarcane using groundwater? If farmers still decide to cultivate them, they should realize that they are in fact using (40 acre inches X Rs. 500 per acre inch =) Rs. 20,000 worth of groundwater for every acre of paddy and double that = Rs. 40,000 worth of groundwater for every acre of sugarcane cultivated. These costs may vary for other parts of India.

Low water, high value crops

Instead of cultivating paddy and sugarcane using groundwater, farmers should cultivate low water high value crops such as flowers, fruits, vegetables, small millets which are economically viable. Farmers should realize that they are drawing a precious resource and hence resort to ‘wise’ use rather than ‘beneficial’ use (Ciriacy-Wantrup). This means, farmers can use groundwater not for paddy, not for sugarcane, but for flowers, fruits, vegetables, using micro or drip or sprinkler irrigation.

Need for irrigation extension

Governments have virtually no program towards Irrigation Extension. Even agricultural extension by Agriculture /Horticulture Departments is relegated since there are no positions of ‘Gramsevaks’. The Governments need to make use of our Agri Engineering graduates offering them hands on training in groundwater, linking them with the Department which handles Groundwater. Even with the Dept of Mines and Geology, Irrigation Department, Minor Irrigation Department, Urban water supply Board, and all the laws such as Irrigation Act of 1965, Land Reforms Act, the latest Groundwater Regulation and Control Acts in different States, groundwater resource has been treated as an ‘orphan’ since there is no agency to practically conserve (like Forest Department which exclusively deals with forestry). Dept of Mines and Geology is more concerned with Mines, since minerals are more ‘valuable’ than ‘groundwater’ !

Green revolution is in fact groundwater overexploitation revolution.

The Governments and farmers need to realize that while our food production and horticulture production has surpassed 300 million tonnes each, this is at the cost of overexploitation of groundwater for irrigation. Farmers need to be educated through creating awareness towards importance of groundwater recharge, which costs around 20 percent of the cost of borewell, and also help to volumetrically measure groundwater through low cost water measuring devices to appreciate the true value of groundwater so that farmer/s use/s groundwater efficiently, effectively, sustainably.

The original Article can be found on.

https://timesofindia.indiatimes.com/blogs/economic-policy/how-crucial-is-groundwater-recharge-in-irrigation/