Increased withdrawals of groundwater resources are accelerating groundwater depletion rates in India, a groundwater depletion hotspot, a new study finds. The study, published today in the journal Science Advances, is led by University of Oklahoma Department of Geography and Environmental Sustainability assistant professor Nishan Bhattarai.
Bhattarai and his collaborators found that under a business-as-usual scenario of groundwater use for irrigation, warming may triple the groundwater depletion rates. Approximately 60% of India's irrigated agriculture depends on the threatened groundwater. The results of the study indicate that adaptation to an increasingly warm climate threatens the security of India's future food and water.
"Without policies and interventions to conserve groundwater, we find that warming temperatures will likely amplify India's already existing groundwater depletion problem, further challenging India's food and water security in the face of climate change," Bhattarai said.
The study uses an empirical model linking groundwater depletion, crop water stress and India's climate. After modeling these relationships across the country, the authors also assessed whether the relationships between these variables differed for India's two major aquifer systems, unconsolidated and consolidated aquifers.
Additionally, the study suggests that climate change may increase the areas of the country where groundwater depletion occurs. Currently, the most overexploited aquifers are in the northwest and south of India, but the study indicates that by 2050 that area may extend to the southwest, the southern peninsula and central India.
The study used a unique dataset combining groundwater depth data from thousands of wells across India, a high-resolution remote-sensing data product measuring crop water stress, and temperature and precipitation data.
Prior studies focused specifically on the effects of climate change and groundwater depletion on crop production rather than the feedback mechanisms between these variables. Those studies also did not account for farmer decision-making. Bhattarai's study considers that farmers may increase irrigation to adapt to increased crop water demand, but groundwater depletion could reduce irrigation abilities over decadal time scales.
Increased water demand means that the warming temperatures increase crop water stress in both the monsoon and winter growing seasons. And, while monsoons provide ample water for crops through precipitation and surface water availability, for consolidated aquifer systems, groundwater depletion is driven by a decrease in monsoon recharge. For unconsolidated aquifer systems, the declines are caused by increased groundwater withdrawal during the winter season.
The study calls for an end to the overexploitation of groundwater withdrawal, citing a need for policies for rationing the power supply and metering electricity usage that has historically allowed farmers to withdraw groundwater on demand. Additional measures include regional water source development and allocation, rewarding those farmers who invest in groundwater recharge, and the reduction or removal of energy subsidies.
The study's coauthors include David B. Lobell of Stanford University, 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, Yadu Pokhrel of Michigan State University, and Meha Jain of the University of Michigan.
