Groundwater Depletion and Associated CO2 Emissions in India

India, the world's largest groundwater user, withdraws about 230-billion-m(3) 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 m(3) from the observation wells (1996-2016) and Gravity Recovery Climate Experiment (2002-2016). The CO2 emissions due to bicarbonate (similar to 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.