The Groundwater Recovery Paradox in South India.

Reported groundwater recovery in South India has been attributed to both increasing rainfall and political interventions. Findings of increasing groundwater levels, however, are at odds with reports of well failure and decreases in the land area irrigated from shallow wells. We argue that recently reported results are skewed by the problem of survivor bias, with dry or defunct wells being systematically excluded from trend analyses due to missing data. We hypothesize that these dry wells carry critical information about groundwater stress that is missed when data are filtered. Indeed, we find strong correlations between missing well data and metrics related to climate stress and groundwater development, indicative of a systemic bias. Using two alternative metrics, which take into account information from dry and defunct wells, our results demonstrate increasing groundwater stress in South India. Our refined approach for identifying groundwater depletion hot spots is critical for policy interventions and resource allocation. Plain Language Summary: Over the last century, groundwater has become an important source of freshwater to meet agricultural and drinking water needs. Increasing use of groundwater has contributed to depletion of groundwater reserves around the world, with India being at the forefront of this problem. Recent studies suggest that groundwater levels have been increasing in South India due to increasing rainfall and political interventions. This finding is at odds with local reports of groundwater stress, and increasing well failures. Our study explains this disagreement by showing that previous conclusions have been skewed by the problem of survivor bias, with wells with data gaps being routinely excluded from analysis of long‐term groundwater storage trends. We find that traditional groundwater trend assessment methods are not suitable for hard‐rock aquifer systems that characterize South India. Indeed, strong correlation exists between climate and groundwater stress and wells with missing data, indicative of a systemic bias. We develop metrics that use data from these wells, and show using these metrics increasing evidence of groundwater stress in South India over the last two decades (1996 to 2016). Our results provide insight into the management of groundwater depletion in India, while highlighting potential biases in groundwater sustainability assessments globally. Key Points: Reported recovery of groundwater levels in South India is at odds with increasing well failures and reports of groundwater stressApparent paradox is explained by survivor bias, where wells with missing data are routinely excluded from analysis of groundwater trendsLong‐term trend analysis is not appropriate for hard‐rock aquifer of South India; alternative metrics developed that highlight groundwater stress [ABSTRACT FROM AUTHOR]