Prioritising Over-Exploited Assessment Units for Groundwater Management Based on Long-Term Storage Depletion of the Aquifers

ABSTRACT India is heavily dependent on groundwater resources for meeting its water requirements. Management of aquifers is thereby an issue of serious concern, particularly in areas where groundwater extraction exceeds the annual replenishment, i.e. Over-Exploited (OE) areas. Our ability to manage a particular resource is contingent upon our capacity to quantify and assess it. Prior to 2022, assessment of groundwater resources in India was carried out at periodic intervals, and since 2022, it has been conducted on an annual basis. According to the latest assessment carried out in 2023, there are 736 Assessment Units (AUs) under the OE category. While this categorisation reflects the yearly inflow-outflow dynamics of the aquifer, it is unable to capture the long-term depletion of aquifer storage, which has already happened. Thus, an over-exploited AU with a consistent ratio of groundwater extraction with respect to replenishment for a continuous period may witness a significant decline in water level or desaturation of the aquifer thus requires urgent groundwater management interventions. In this paper, we have attempted to prioritise over-exploited AUs for groundwater management interventions based on the extent of ‘Long-term Storage Depletion’ (LSD) in the phreatic aquifers of the country as a whole with detailed analysis for the State of Haryana. The decadal average post-monsoon water level from 1991-2000 has been considered as the reference for this study. The storage loss and total aquifer storage at the reference year have been estimated using the average post-monsoon water level of 2022, the water level at the reference period, and the thickness of the phreatic aquifers. Ultimately, the LSD was computed by expressing the storage loss as a percentage of the total aquifer storage at the reference level. Based on the extent of LSD, the over-exploited AUs were further classified into: i) “Incipient” (LSD ≤ 10%), ii) “Moderate” (LSD > 10% and ≤ 25%), iii) “High” (LSD > 25% and ≤ 50%), and iv) “Severe” (LSD > 50%). Out of the 736 over-exploited AUs of the Country, 395 AUs (53%) have been classified as ‘Incipient’, 162 AUs (22%) as ‘Moderate’, 130 AUs (18%) as ‘High’, and 49 AUs (7%) as having ‘severe’ storage depletion. These over-exploited AUs with ‘Severe’ and ‘High’ LSD, fall mostly across Delhi, Gujarat, Haryana, Karnataka, Punjab, Rajasthan, and Uttar Pradesh, and require immediate implementation of groundwater management interventions and regulatory measures.