(Adapted from press release by Jim Erickson, University of Michigan)

Farmers in India have adapted to warming temperatures by intensifying the withdrawal of groundwater used for irrigation, according to a new study coauthored by Stanford environmental scientist David Lobell. If the trend continues, the rate of groundwater loss could triple by 2080, further threatening India’s food and water security, according to the paper, published Sept. 1 in Science Advances.

“By looking at how farmers have responded to warm years in the recent past, we can see a dramatic increase in irrigation in hotter years,” said Lobell, the Gloria and Richard Kushel Director of Stanford’s Center on Food Security and the Environment and professor of Earth system science in the Stanford Doerr School of Sustainability. “We expected they would water more when it’s hot, but the magnitude surprised us.” 

Reduced water availability in India due to groundwater depletion and climate change could threaten the livelihoods of more than one-third of the country’s 1.4 billion residents  and has global implications. India recently overtook China to become the world’s most populous nation and is the second-largest global producer of common cereal grains including rice and wheat.

The study analyzed historical data on groundwater levels, climate, and crop water stress to look for recent changes in withdrawal rates due to warming. The researchers also used temperature and precipitation projections from 10 climate models to estimate future rates of groundwater loss across India.

“Using our model estimates, we project that under a business-as-usual scenario, warming temperatures may triple groundwater depletion rates in the future and expand groundwater depletion hotspots to include south and central India,” said study lead author Nishan Bhattarai of the Department of Geography and Environmental Sustainability at the University of Oklahoma.

Previous studies have focused on the individual effects of climate change and groundwater depletion on crop production in India. Those studies did not account for farmer decision-making, including how farmers may adapt to changing climate through changes in irrigation decisions.

The study takes into account the fact that warmer temperatures may increase water demand from stressed crops, which in turn may lead to increased irrigation by farmers.

Previous studies found that climate change could decrease the yield of staple Indian crops by up to 20% by mid-century. At the same time, the country’s groundwater is being depleted at an alarming rate, primarily because of water withdrawal for irrigation.

For the newly published study, the researchers developed a dataset that contains groundwater depths from thousands of wells across India, high-resolution satellite observations that measured crop water stress, and temperature and precipitation records.

Most climate models call for increased temperature, increased monsoon (June through September) precipitation and decreased winter precipitation in India over the coming decades. The research team found that warming temperatures coupled with declining winter precipitation more than offset added groundwater recharge from increased monsoon precipitation, resulting in accelerated groundwater declines.

Across various climate-change scenarios, their estimates of groundwater-level declines between 2041 and 2080 were more than three times current depletion rates, on average.

Lobell is also the William Wrigley Senior Fellow at the Stanford Woods Institute for the Environment, and a senior fellow at the Freeman Spogli Institute for International Studies and the Stanford Institute for Economic Policy Research.

The study’s senior author is Meha Jain of the University of Michigan’s School for Environment and Sustainability. Other coauthors include Balwinder Singh of the International Maize and Wheat Improvement Center in India and the Department of Primary Industries and Regional Development in Western Australia, Ram Fishman of Tel Aviv University, William Kustas of the U.S. Department of Agriculture, and Yadu Pokhrel of Michigan State University.

The research was funded by a NASA Land-Cover Land-Use Change Grant and a NASA new investigator program award to Jain. The research was supported in part by the U.S. Department of Agriculture’s Agricultural Research Service.