Changes in groundwater storage in the Southern plain of Western Nepal: Insights from remote sensing, modeling, and field studies

Groundwater (GW) levels in many parts of the world are depleting, including the western Terai region of Nepal, yet the extent of depletion and availability of the resource remain unknown. This study intends to characterize the state of GW potential and depletion in the southern plain of Western Nepal by applying field-based, model-based, and remote-sensing-based approaches. Borehole lithologs were used to evaluate storage potential. Observed GW level data, along with GRACE satellite data, were used to characterize the depletion. Primary data were collected to assess annual GW abstraction. The Static storage potential of a deep confined aquifer is estimated in a range of 8–800Mm³, and that of an unconfined shallow aquifer is 7,500–15,000Mm³. Regional terrestrial water storage (2004–2022) is trending downward. Locally, depletion (2008–2023) across municipalities ranges from negligible (0.1 m, Tikapur Municipality) to high (3.3 m, Gauriganga Municipality). Average annual GW abstraction for agriculture and domestic needs is estimated as 378.39Mm³ and 44.38Mm³, respectively. Based on insights from field and model-based studies, as well as techniques documented in literature, it is recommended to consider non-structural strategies for the conservation of GW. The findings of this study are constructive for better planning and future development of GW resources in the area.