Elevation-dependent groundwater control on baseflow in a himalayan catchment: an integrated isotopic-hydrological assessment.

Integrating the Variable Infiltration Capacity (VIC) hydrological model with stable isotope tracers, the study establishes a robust method for quantifying baseflow contributions, providing a reliable tool for Integrated Water Resource Management (IWRM) and allowing for cross-validation of simulated groundwater dynamics. Extensive seasonal sampling of river water, springs, and precipitation across elevation gradients was combined with calibrated hydrological simulations. Isotope-based mixing models and VIC outputs show good agreement, revealing a pronounced elevation-dependent increase in baseflow contribution during the dry season. Our study reports that baseflow is responsible for sustaining perennial streamflow,with contribution exceeding 70% at elevations above 1500 m, and up to 97.0 ± 1.5% at higher elevations (> 3000 m) , thus acting as the primary water resource for supporting dry-season water demand. This quantification is critical for ensuring sustainable groundwater resources upstream and managing river water scarcity in downstream regions. The findings in this study directly support India's Jal Jeevan Mission, Springshed Management, and National Water Policy by providing evidence-based protection for groundwater-fed springs, which are vital to rural drinking water security. This integrated framework allows stakeholders to identify hydrologically sensitive zones and maintain ecological flows amidst changing climate patterns.