Excerpts from “Groundwater depletion and associated CO2 emissions in India” by Vimal Mishra, Akarsh Asoka, Kamal Vatta, and Upmanu Lall, Civil Engineering and Earth Sciences, Indian Institute of Technology-Gandhinagar*
India, the world’s largest groundwater user, withdraws about 230 billion m3groundwater annually for irrigation. Excessive groundwater pumping in India leads to rapid groundwater depletion and CO2 emissions. Here, using multiple data sources (observation wells and GRACE) 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 annualCO2 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 of122 to 199 billion m3from the observation wells (1996-2016) and GRACE (2002-2016).The CO2 emissions due to bicarbonate (~ 0.72 million tons per 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 dataset 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.
Groundwater is a lifeline for food and water security for millions of people in India, the largest consumer of groundwater in the world. About 88% of the total groundwater withdrawal in India is used for irrigation. Groundwater pumping for irrigation combined with the weakening of the Indian summer monsoon has resulted in widespread groundwater depletion in India in the last 20 years. The rate of abstraction in many regions is higher than groundwater recharge, causing a recurrent water stress, persistent groundwater depletion and long-lasting impacts on stream flow, lakes, and wetlands.
The Indo-Gangetic plain and northwest India have experienced a severe decline in groundwater storage and corresponds to one of the largest groundwater footprints in the world. After the green revolution in the 1970s, the net irrigated area in India expanded from 31 to 60 million hectares between 1970 and 2007, out of which nearly 80% was contributed by groundwater.
About 60% of irrigation in India was sourced from groundwater during 2000-2007. The expansion of groundwater-based irrigation in India is due in part to the Central government procuring wheat and rice from arid regions and the governments in those states providing highly subsidized electricity for agricultural pumping systems. The result is a rapid depletion in groundwater in India. While the impacts of unsustainable groundwater consumption on food and fresh water security are well documented, the role of groundwater depletion in India on CO2 emissions due to bicarbonate and pumping remains unrecognized. Moreover, approaches to managing groundwater sustainably in India are not well established.
Here using the observational and satellite-based datasets, we first identify the spatiotemporal extent of groundwater depletion during 1996- 2016. We use a well-distributed record of groundwater related measures (e.g., specific yield, bicarbonate concentration, electric pumps) to estimate CO2 emissions due to due to bicarbonate and pumping in India. Using a unique field survey dataset, we show that water savings in irrigation can be a prominent driver of sustainable management of groundwater in India.
While unsustainable depletion of groundwater due to pumping hampers food and freshwater security, it also results in CO2 emission to the atmosphere. However, we find that combined CO2 emissions because of bicarbonate extraction, and pumping is less than 2-7% of total annual CO2 emissions from India. Considering the size of irrigated agriculture and groundwater pumping in India, annual CO2 emission related to groundwater based irrigation is not a significant contributor to the total emissions (which may or may not have included these emissions accurately).
Moreover, we report that bicarbonate extraction causes CO2 emissions about 0.72 million tons per year, which is considerably lower than the estimates for the USA. Lower estimates of CO2 emissions in India can be attributed to lower bicarbonate concentrations in comparison to the USA. Therefore, our results do not support the argument that groundwater depletion is a significant unreported source of CO2 emissions as reported in reference.
CO2 emissions due to annual groundwater withdrawal of more than 222 billion m3 (CGWB, 2014) is about 32.01-131.74 million tons, which is an insignificant fraction of the total CO2 emissions of ~ 2 billion tons from India. CO2 emission due to groundwater pumping can be reduced by using solar and wind power instead of electricity and diesel based pumping systems and also by improving the pumping efficiency.
However, we notice that the regions (Indo-Gangetic Plain and northwestern India) with the higher groundwater abstraction and depletion have relatively low potential for the use of solar and wind power, indicating that these states require additional measures to reduce the dependence on electricity and diesel based groundwater pumping. Further, availability of solar and wind energy based pumping will enhance groundwater depletion, which is a major environmental degradation problem in the country.
Reduction in subsidy in electricity prices can be a useful measure to reduce the pumping and encourage farmers for appropriate crop choices. Electricity cost of pumping groundwater for irrigation varies widely in India from $28/ha in Uttar Pradesh (lowest) to $560/ha (highest) in Karnataka; therefore, the abolition of subsidies may significantly reduce groundwater pumping and CO2 emission.
For India, the environmental problem of groundwater depletion is much more serious than the associated CO2 emissions, and hence there is an urgent need for regulation of groundwater use. We demonstrate that technological intervention through agro-extension systems can result in sustainable management of depleting groundwater and CO2 emissions in Punjab. Additionally, all forms of electricity subsidy, including that for the solar need to be curbed and an effective national groundwater monitoring and extraction program is needed. In the regions that are most affected by groundwater depletion (northwestern India and Indo-Gangetic Plain), a poor choice of crops and irrigation technologyis the primary reason.
For instance, despite the groundwater depletion in Punjab, the total area under rice has increased from 10% in 1975 to 38% in 2010, which resulted in a massive withdrawal of groundwater for irrigation leading to an overdraft condition. Average water requirement for water-intensive crops such as rice (1200 mm) and sugarcane (2000 mm) is far more significant than the other cereal crops.
The proper choice of crops, especially in northwestern India and Indo-Gangetic Plain can be a useful measure to reduce unsustainable extraction of groundwater. Along with appropriate crop choices, improving irrigation and water use efficiencies can reduce the amount of excessive extraction of groundwater by two-thirds. Therefore, technology and policy related decisions are required at multiple levels ensure sustainable management of groundwater resources in India.
*Columbia International Project Trust (CIPT), New Delhi; Columbia Water Center, Columbia University, Columbia, New York
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