Concealed Groundwater Day Zero: An Uncertainty–Scarcity–Vulnerability Framework for Assessing Groundwater Unsustainability and Hydro-Social Risk in Bangladesh

Groundwater depletion is a major environmental and socio-economic challenge in Bangladesh. This study evaluates the spatiotemporal dynamics of groundwater depletion and hydro-social vulnerability using 400 Bangladesh Water Development Board monitoring wells for 1990–2019. The conceptual basis is the Reliability–Resiliency–Vulnerability (RRV) framework; operationally, it is adapted into three normalized groundwater-stress components: Uncertainty (U, the frequency of threshold exceedance and therefore a proxy for unreliability), Scarcity (S, persistence or non-recovery after a drought episode), and Vulnerability (V, severity of groundwater-level deficit). These components are combined into a Groundwater Day Zero Index (DZI), while population and irrigation layers are used separately to characterize exposure. Drought episodes are defined when standardized groundwater level falls below −1 standard deviation of the long-term mean. Results indicate widespread depletion, with reported rates of about 0.15–0.21 m yr−1 in stressed northwestern and central regions. Dhaka has a severe DZI (≈0.91; >0.75), while much of the Barind Tract falls within high-to-severe conditions (≈0.72–0.78). National mean component values (U = 0.46, S = 0.52, V = 0.57) indicate predominantly moderate-to-high stress. Spatial associations between DZI and irrigation/urban intensity (r = 0.74, p < 0.01), population density (r = 0.76, p < 0.01), and irrigation intensity (r = 0.81, p < 0.01) provide convergent evidence that the index identifies areas with substantial anthropogenic groundwater pressure. The DZI is intended as a diagnostic screening indicator rather than a prediction of the calendar date of groundwater failure. Its principal value is to combine the frequency, persistence, and severity of groundwater stress in a form that supports spatial prioritization and periodic updating as new monitoring and climate information become available.