India is the largest user of groundwater in the world. It uses an estimated 230 km3 of groundwater per year, which is over a quarter of the global total. About 85 percent of rural drinking water needs, 65 percent of irrigation needs and 50 percent of urban drinking water and industrial needs are fulfilled with groundwater. A study, An Untold Story of Groundwater Replenishment in India: Impact of Long-Term Policy Interventions, published in the journal Advances in Water Resources indicates that groundwater depletion in the north and east India will affect over 120 million people in the Gangetic states. The study by Prof. Abhijeet Mukherjee from the Indian Institute of Technology, Kharagpur and Dr Soumendra Nath Bhanja, Athabasca University, Canada compiled the first estimates of usable groundwater storage at the state-level across India using both in-situ and satellite-based measurements.
The in-situ data has been retrieved from a well-maintained network of groundwater-level monitoring locations in India. Groundwater-level data was used from 3,907 in-situ monitoring wells across the country and the total usable groundwater storage was estimated between 2005 and 2013. The study combined borehole data from Central Ground Water Board, rainfall data and satellite data from NASA's Gravity Recovery and Climate Experiment (GRACE) launched in 2002.
Groundwater storage depletes in most parts of the country
The estimates show rapid depletion of usable groundwater storage in most parts of northern and eastern India during 2005-2013, losing 8.5 cubic kilometre per year (km3/year) and 5 km3/year of total groundwater respectively. More than 85 percent of the groundwater usage in India is linked with irrigation abstraction practices during non-monsoonal months. Large-scale depletion could have unforeseen consequences in future food security.
India's northern and eastern states such as Assam, Punjab, Haryana, Uttar Pradesh, Bihar, and West Bengal saw a rapid decline in usable groundwater between 2005 and 2013, raising the risk of severe droughts, food crisis, and drinking water for millions of people, the study found. Parts of the Indus-Ganga-Brahmaputra basin mostly show reducing groundwater levels, whereas parts of western and southern India show increasing trends. More than four metre groundwater decline have been observed during the last decade in the Indian states of Delhi, Haryana, Punjab, Rajasthan and West Bengal.
The fertile alluvial plains of the Gangetic basin are densely populated and are conducive for irrigational activities. The rapid depletion of groundwater in the Gangetic basin is linked to surface water quantity reduction in Ganges river during the recent summers. These depletion trends and practices have not only affected the groundwater storage but also declined the flow in the adjoining rivers, including the Ganga, leading to it drying in recent summers. The study indicates that the depletion is positively linked to the practice of water-intensive crops farming in these states and not necessarily related to the change in rainfall patterns.
As per the study, “The rapidly growing demands in these areas are directly proportional to the increasing population, the introduction of water-intensive crops (e.g., boro rice), and changes in cropping pattern (e.g., replacing food crop by cash crop) and coincide with the areas showing highest groundwater storage depletion…In these areas, increases in agricultural food productions have resulted at the cost of non-renewable loss in groundwater volume at an alarming rate.”
Reduction in groundwater withdrawal leads to replenishment in some states
The study indicates that southern and western Indian states like Andhra Pradesh, Maharashtra, Gujarat and Chhattisgarh show trends of replenishing usable groundwater storage. The reasons for replenishment include “the reduction in irrigation-linked groundwater withdrawal, change in agricultural practice, increasing artificial recharge and surface water irrigation increase (Bhanja et al. 2017b).
As per the study, Haryana, which gets annual precipitation of 689 millimetres (mm), holds the highest levels of usable groundwater with 3,593 centimetres (cm) while Himachal Pradesh with precipitation of 1,147 mm per year has the lowest UGWS level of 520 cm.
Assam and some parts of eastern India seem to be losing the usable groundwater storage at the highest rate, within the study period, as per the study. Many of these states are now intermittently getting affected by the "groundwater drought" in recent summers. The study suggests that these summer groundwater droughts would intensify in future, to become severe to very severe by 2050, with the possibility of spreading over all seasons. The rapid depletion in usable groundwater storage would accelerate the decline in food production and the availability of drinking water, two of the prime goals of achieving UN Sustainable Development Goals 2030.
The groundwater replenishment in certain states of India could be because of a combination of government policy changes and grassroots efforts of local communities, who have undertaken several projects over the last several years in the form of efficient groundwater management and utilisation policies.
The full text of the study can be accessed here