Groundwater Depletion and Associated CO2 Emissions in India.

India, the world's largest groundwater user, withdraws about 230‐billion‐m3 groundwater annually for irrigation. Excessive groundwater pumping in India leads to rapid groundwater depletion and CO2 emissions. Here using multiple data sources (observation wells and Gravity Recovery Climate Experiment) to estimate groundwater depletion in India, as well as the associated chemistry and the pumping energy requirements, we provide the first estimate of the potential CO2 emissions due to bicarbonate extraction (CO2 release due to lowering of groundwater table) and groundwater pumping. We show that combined annual CO2 release due to bicarbonate extraction and pumping in India is approximately 32.01–131.74 million tons (31.29–131.02 million tons for pumping and 0.72 million tons for bicarbonate). The total estimated groundwater depletion in India is in the range of 122 to 199 billion m3 from the observation wells (1996–2016) and Gravity Recovery Climate Experiment (2002–2016). The CO2 emissions due to bicarbonate (~0.72 million tons/year) are dominated by those due to groundwater pumping (31.29–131.02 million tons/year) in India. However, the total (pumping and bicarbonate) estimated annual CO2 emission from groundwater is less than 2–7% of the total (annual) CO2 emission from India. Based on our unique data set collected from more than 500 farmers in Punjab, we show that a low‐cost intervention for irrigation scheduling based on soil moisture information can provide a sustainable solution by reducing groundwater pumping and CO2 emissions. The environmental problem of groundwater depletion in India is much more serious than the associated CO2 emissions, and hence, there is an urgent need for a regulation of groundwater use. Plain Language Summary: Groundwater depletion in India remains one of the most critical issues related to future food and freshwater security. Groundwater depletion causes a significant emission of CO2 in the United States as shown in the previous study. Since India is the largest consumer of groundwater, we hypothesized that CO2 emission due to groundwater depletion in India would be considerable. We, however, find that CO2 emission in India due to groundwater depletion and pumping is only about 2% of the total emissions combined from all the sectors. Our results show a significant decline (200 billion m3) in groundwater in India, especially in the northwestern and northcentral regions. We show that curbing the depletion of groundwater in India is a major challenge rather than reducing CO2 emission due to groundwater depletion and pumping. Key Points: The total estimated groundwater depletion in India is in the range of 122 to 199 billion m3The CO2 emissions due to bicarbonate is ~0.72 million tons/yearThe environmental problem of groundwater depletion in India is much more serious than the associated CO2 emissions [ABSTRACT FROM AUTHOR]