(CNN)Hundreds of millions of people in India face a serious threat to their livelihoods and food security due to overexploitation of vital water supplies, according to the authors of a new study.
India's groundwater crisis threatens food security for hundreds of millions, study says
India is one of the world's biggest crop producers and more than half of its 1.3 billion people rely on agriculture for their livelihoods. But the groundwater that makes up 40% of the country's water supply has been steadily depleting for years.
The study, published Wednesday in the journal Science Advances, found that overuse of groundwater could cause winter harvests in some regions of the country to fall up to two thirds by 2025.
A team of international researchers analyzed satellite imagery and census data to gauge the impact on winter harvests, which account for 44% of the country's annual cropped acreage for food grains, according to the study. Winter agriculture relies heavily on groundwater irrigation -- as opposed to other seasons that can take advantage of heavy monsoon rains.
Indian food production has skyrocketed since the 1960s, as farmers began widely using tube wells, which draw water from deep underground. This has allowed them to continue farming even during dry seasons when there isn't rain or sufficient surface water -- but over-extraction has left "critically low groundwater availability" in the country's northwest and south, according to the research.
"Many studies have shown that India has large groundwater depletion, but to date it has been unclear what the impacts of this depletion could have on agricultural production," said lead author Meha Jain, an assistant professor at the University of Michigan's School for Environment and Sustainability.
The researchers found that if farmers in over-exploited regions lose all access to groundwater, and if that irrigation water isn't replaced by water from other sources, winter harvests could decrease by 20% nationwide and by 68% in the most severely affected areas.
This is a worst-case scenario, and the damage could be mitigated if authorities take action and adopt alternative irrigation options, the study said. The government has already been widely pushing the adoption of canal irrigation, which diverts surface water from lakes and rivers, and could help offset some of the losses.
But it's far from a perfect solution -- even if all regions currently using depleted groundwater switched to canal irrigation, winter harvests could still decline by 7% nationwide and by 24% in the worst hit locations, according to the study.
And canal irrigation comes at its own cost -- it would mean farmers are more vulnerable to weather changes, since lakes and rivers depend on rainfall. Groundwater is also a more equitable way to distribute water across villages, since wells are decentralized as opposed to large-scale canal projects.
"Our results highlight the critical importance of groundwater for Indian agriculture and rural livelihoods, and we were able to show that simply providing canal irrigation as a substitute irrigation source will likely not be enough to maintain current production levels in the face of groundwater depletion," said Jain in a news release.
Instead, the government needs to adopt a wide range of strategies -- for instance, switching from winter rice to less water-intensive cereals, the use of sprinklers and drip irrigation to conserve water, and policies to increase the efficiency of irrigation canals, according to the study.
India's water crisis has been building for years, gaining international attention in 2019 when Chennai, the country's sixth largest city, faced an acute water shortage.
The city's four main reservoirs ran nearly dry due to insufficient rainfall and low groundwater levels. Water had to be trucked into Chennai from other states and regions, forcing hundreds of thousands of residents to stand in line for hours in the summer heat to receive rationed water.
It's a national problem: 100 million people, including those in the large cities of Delhi, Bangalore and Hyderabad, face the threat of groundwater running out entirely, according to a 2018 report by Niti Aayog, an Indian government think tank.
The agricultural sector has been one of the hardest hit. The regions with the most severe water depletion fall along India's food bowl -- states like Maharashtra and Tamil Nadu, which support the whole country's food security, said Bharat Sharma, scientist emeritus at the International Water Management Institution, who was not involved in the study.
"The water table is depleting very fast in north India ... That is why the farmers started making use of groundwater, because surface water was not available and the explosive use of groundwater began," he said. "The cropping system we are using requires more water than is available."
The devastating effects of climate change have also added to the difficulties facing