Impact of large-scale managed aquifer recharge in sustaining agricultural groundwater use: A case study of shallow hard-rock aquifer region of western India

To mitigate groundwater depletion and enhance groundwater storage for irrigation, managed aquifer recharge (MAR) is promoted globally. There has long been concern that MAR when applied in rural semi-arid areas underlain by hardrock aquifers, may not always be effective in terms of sustaining groundwater use and mitigating negative impacts of droughts. This paper presents a case study of a catchment underlain by shallow hardrock aquifer in the semi-arid western Indian state of Gujarat. Gujarat, impacted by widespread groundwater depletion, has invested heavily in MAR with an estimated ~ 100,000 structures installed (mostly check dams, CD) over the past two decades. The study estimated and compared the dynamics of increased recharge via CDs, irrigation demand and groundwater storage in the catchment. We find that the region underlain by hard rock aquifer has limited aquifer storage which is replenished and withdrawn annually, thus limiting the year-to-year buffer storage. Additionally, supply-demand feedback loops have led to significantly higher irrigation demand which has outstripped the increase in supply via CD recharge. This increase in demand along with overreliance on limited aquifer storage and low surface runoff in dry years (rainfall ~ 350-400 mm/year) means that CD capacity to enhance irrigation supply and mitigate negative impacts of drought is very restricted. On the contrary, this has increased vulnerability, with up to ~ 70 % of irrigation demands remaining unmet in dry years. This is symptomatic of sociohydrological phenomenon “reservoir effect” where overreliance on increased supply to reduce vulnerability has backfired. We also find that for good rainfall years, CDs do increase irrigation supply but that can only partially compensate for increased irrigation demand. This results in lower groundwater storage in period after the construction of CDs. The results call into question of the efficacy of MAR as a solution for enhancing groundwater storage and drought mitigation strategy in semi-arid regions underlain by hard rock. Our results show the limitation of technological solutions focusing on augmenting supply and calls for a realistic assessment of MAR explicitly accounting for coupled natural-human systems to reveal unintended and emergent dynamics that can lead to negative externalities and increased vulnerability.