A Deficit-Based Groundwater Drought Index (GWDI): Concept, Methodology, and Application in Hard-Rock Aquifers

Abstract

Effective assessment of groundwater drought requires indicators that reflect subsurface water stress rather than relying solely on surface hydro-meteorological signals. The Groundwater Drought Index (GWDI), endorsed within India’s national drought assessment framework, quantifies groundwater drought by measuring deviations of observed groundwater levels from long-term reference conditions. This study provides a detailed methodological appraisal of GWDI, encompassing its conceptual foundation, mathematical formulation, drought severity categorization, and linkage with non-parametric trend detection techniques. Post-monsoon groundwater level records from a semi-arid basaltic aquifer system are used to demonstrate the applicability and reliability of the index. The analysis shows that GWDI successfully identifies persistent groundwater stress, including periods characterized by above-average rainfall. The findings highlight GWDI as an operationally robust, scientifically credible, and policy-oriented tool for groundwater drought monitoring and sustainable management of hard-rock aquifer systems.