How important is groundwater recharge in irrigation?


India is the largest pumper of groundwater in the world, pumping twice that of the United States and 6 times that of Western Europe, pumps around 75 acre inches per well from around 30 million wells in ‘irrigation. About 70% of irrigation in India comes from groundwater. It is crucial to appreciate the role of natural groundwater recharge and how it influences pumping from an irrigation borehole. Thus, groundwater recharge is crucial for sustainable extraction. India’s hard rock areas form 65% of its geographic area where rainfall recharge is barely 10%. Therefore, if the farmer receives about 750mm of rainfall per year, only 75mm is natural recharge and the rest runs off.

Volume of rainwater pumped compared to recharge

On an acre of land of 4000 square meters, rainfall of 750 mm per year implies as below: 750 mm of rainfall equals 0.75 meters. On 4000 square meters, a rainfall of 0.75 meters implies = 0.75MX 4000 Sq. M = 3000 cubic meters. Let 1 cubic meter = 1000 liters of water, 3000 cubic meters = 3000000 liters of water. Since 1 gallon of water = 4.54 liters, 3,000,000 liters of water = 660,793 gallons, which equals 29 acre inches or ha cm since 1 acre inch or 1 ha cm = 22,611 gallons of ‘water. Therefore, 1 acre with 750 mm of precipitation is approximately equivalent to 29 acre inches of rainwater assuming modest evapotranspiration. Each 5 cm irrigation for paddy is about 2 acre inches for one acre.

Unsustainable groundwater extraction

Considering groundwater recharge from 10% rainfall, out of 29 acre-inches, only 2.9 acre-inches will enter the aquifer. An irrigation well extracts approximately 100 inches of an acre of groundwater. On average, one irrigation well irrigates about 3 acres. So for three acres, the total recharge is 2.9 acre inches X 3 acres = 8.7 acre inches or about 9 acre inches. Thus, by recharging 9 acre inches of water, the farmer pumps 100 acre inches of water per well on average each year, leaving approximately 90 acre inches of space to be consciously or unconsciously recharged by other areas. Thus, extracting 100 inches of an acre from a well and recharging only 9 or 10 inches of an acre is overexploitation leading to massive borehole failure forcing farmers to invest in drilling new wells continuously.

Groundwater Extraction Awareness

Therefore, it is crucial to educate farmers that they are abstracting about 100 acre inches of groundwater from an irrigation well, that they are actually extracting groundwater from at least 30 acres of additional land, since each acre only recharges about 3 acre inches of water per year. Unless groundwater recharge programs are undertaken on a large scale, groundwater wells will face premature/initial failures. Studies by the Agricultural Economics Department of UAS Bangalore funded by the Ford Foundation from 1995 to 2005 indicate that (1) the probability of failure of a well is about 0.4; (2) open wells / dug wells have all but disappeared due to the advent of deeper boreholes over time (3) the amortized cost of groundwater per acre-inch ranges from Rs. 300 to Rs. 400 disregarding the cost of electricity (4) to raise one inch of an acre of water from the ground, the cost of electricity is around Rs. 100, which implies Rs. 10,000 per year per well for 100 acre inches (5) Total groundwater cost including electricity ranges from Rs. 400 to Rs. 500.

Implications of paddy and sugarcane cultivation using groundwater

Farmers and our government, if they are truly concerned about precious and scarce groundwater, should first think about the current cropping pattern in well irrigation. For example, how ethical is growing paddy/sugar cane using groundwater? If farmers still decide to cultivate them, they must realize that they are actually using (40 acre inches X Rs. 500 per acre inch =) Rs. 20,000 groundwater for each acre of paddy and double = Rs. 40,000 groundwater for every acre of sugarcane grown. These costs may vary for other parts of India.

Low water content, high value crops

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

Need for irrigation extension

Governments have virtually no irrigation extension programs. Even agricultural extension by agriculture/horticulture departments is relegated since there are no ‘Gramsevaks’ posts. Governments need to tap into our agricultural engineering graduates by providing hands-on groundwater training, linking them to the department that manages groundwater. Same with the Department of Mines and Geology, Department of Irrigation, Department of Minor Irrigation, Urban Water Supply Board and all laws such as the Irrigation Act 1965, land reform law, latest groundwater regulation and control laws in different states, groundwater resources have been treated as “orphan” as there is no agency to practically conserve it ( such as the Forestry Department which deals exclusively with forestry). The Department of Mines and Geology is more interested in Mines, because minerals are more “precious” than “groundwater”!

The green revolution is in fact a revolution of overexploitation of groundwater.

Governments and farmers need to realize that while our food and horticultural production has exceeded 300 million tonnes each, this comes at the cost of over-exploitation of groundwater for irrigation. Farmers need to be educated by making them aware of the importance of groundwater recharge, which costs around 20% of the cost of the borehole, and also helping to measure groundwater volumetrically through groundwater metering devices. low cost water in order to appreciate the true value of groundwater so that farmers/s use groundwater efficiently, effectively and sustainably.



The opinions expressed above are those of the author.



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