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Depleted Aquifers Could Decrease India’s Winter Harvest Dramatically

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Tube wells, drilled bore holes that use stainless steel pipes to reach deep below the surface, have supplanted traditional dug wells in India over the past 50 years, leading to huge gains in food production. | Courtesy of Meha Jain

As aquifers in India dry up over the next decade, farmers who rely on groundwater for irrigation may see disastrous losses to annual production, according to a new study.

If farmers were to lose access to groundwater from aquifers predicted to be at critically low levels by 2025, the amount of land planted in the winter growing season could decrease by as much as 68% in the most threatened regions and 20% nationally, an international team of researchers announced in the Feb. 24 issue of Science Advances.

This worst-case scenario is unlikely to fully unfold but highlights the urgency of the problem for the 600 million Indians who rely on farming for their primary livelihood, the 1.3 billion people they feed domestically and the more than 100 countries that import their produce.

“This is important research that better defines the potential consequences of groundwater depletion on agricultural production in India,” said Matthew Rodell, a hydrologist at NASA’s Goddard Space Flight Center who leads projects that monitor groundwater storage changes and was not involved in the new study. “The dangers of such an outcome cannot be overstated.”

Global groundwater reserves, the source of irrigation for 40% of the world’s agricultural production, are rapidly depleting, and the situation is particularly acute in India. In the 1960s, traditional dug wells across the country began to be supplanted by tube wells, drilled bore holes that use stainless steel pipes to reach deep below the surface. This new source of irrigation led to huge gains in food production, allowing farmers to plant in the largely dry winter. Though it is still secondary to the monsoon season, which lasts from late May to early October, the winter growing season now accounts for 44% of India’s grain yield.

While scientists know that many of India’s aquifers are just a few years away from becoming exhausted, the exact impact of this depletion on crop production has proven hard to calculate. The few studies on the topic have relied on coarse, district- or state-level agricultural census statistics that do not distinguish between whether a crop is irrigated by groundwater or other sources, such as canals.

“We have been quite good at finding what the environmental issues are, what we are doing badly — overusing groundwater for example,” said Carole Dalin, an associate professor at University College London who has studied the amount of groundwater depletion embedded in the international food trade and was not involved in the new study. “There is indeed less work on what the consequences will be and, more importantly, what we can do to avoid them.”

To estimate what the loss of access to groundwater would mean for the winter harvest, Meha Jain, an assistant professor of geospatial data sciences at the University of Michigan, and colleagues based in the U.S., Israel and India analyzed satellite images taken by NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS). The researchers began by determining what percentage of a given plot of land was planted during the winter growing season. Thanks to MODIS’s fine resolution — each pixel represents one square kilometer — they were then able to tie the satellite imagery to village-level census data on the type and amount of irrigation used by farmers.

 

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Images captured by MODIS in Nov. 2020 showed a blanket of smoke over northwestern India following crop fires in the region. | NASA

Groundwater provides more than 60% of India’s total irrigation, and some regions are more dependent on it than others. One of the areas in which the situation is most dire is the northern Indo-Gangetic Plain, where most of the country’s wheat is grown, the researchers found. Because of the Indo-Gangetic Plain’s outsize importance, if its wells were to become nonfunctional, the decrease in available calories would affect the whole subcontinent.

“There would be devastating impacts,” said Jain, the study’s lead author.

With empty aquifers, winter cropped area could decrease by more than two-thirds in the northwest and central regions and one-fifth in the country as a whole, the study shows. Replacing groundwater with canal irrigation, which the Indian government is promoting widely alongside drip and sprinkler irrigation, would mitigate the losses but would not allow farmers to match current yields. If farmers switch to canal irrigation, the decrease would be limited to 24% in the worst regions and 7% nationally.

The new study could help policymakers and farmers around the world decide how to adapt as groundwater reserves gradually disappear. In addition to expanding surface irrigation, interventions including planting less water-intensive crops and improving water-use efficiency will be necessary to avoid a significant change to the annual harvest.

“It’s going to be a combination of these strategies that will help farmers maintain levels of production despite groundwater depletion over the coming decades,” Jain said.

 

 

Author

Adam D. Cohen

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