Surface water groundwater interaction in water-stressed semi-arid western India: Insights from environmental isotopes

Understanding the groundwater-surface water interactions and groundwater recharge mechanism is paramount in the arid and semi-arid region which covers nearly 1/3rd of the continental area globally and depends on groundwater to sustain the ecology and livelihood of the people. One such region is semi-arid western India. This study uses seasonal isotopic (δ18O and d-excess) differences to study groundwater dynamics in semi-arid western India, in conjunction with the isotopic composition of India Summer Monsoon (ISM) to understand the rainfall - groundwater relationship, variation in recharge characteristics and quantification of groundwater recharge by rain. Some of the Important results of this study are (1) Temporal variation in the isotopic composition of shallow groundwater reveals that only ∼47% of the area is recharged by ISM rainfall; (2) Isotopic enrichment in post-monsoon season in certain regions (∼25%) indicates that deep static non-replenishable groundwater is extracted for irrigation which finds its way into shallower aquifers; (3) ∼25% (0.52 Billion Cubic Meters) of the available dynamic groundwater resource in South Gujarat is lost as submarine groundwater discharges into the Arabian Sea; (4) Groundwater in the coastal area near the Gulf of Kachchh is recharged by hypersaline waters from salt pan.