Multi-method estimation of groundwater recharge in the Fetam catchment, Upper Blue Nile Basin, Ethiopia

Reliable groundwater resources are essential in catchments characterized by strong rainfall seasonality and intermittent surface-water availability, such as the Fetam catchment in the Upper Blue Nile Basin, Ethiopia. In this study, groundwater recharge was quantified using a multi-method approach to reduce method-dependent uncertainty and provide a defensible recharge range for sustainable groundwater management. Five independent methods were applied: soil moisture balance, baseflow separation of streamflow, chloride mass balance, water-table fluctuation, and catchment water balance. Hydro-meteorological data, groundwater-level measurements, hydrochemical analyses, land use, soil, and hydrogeological information were integrated and spatially aggregated using Thiessen polygon weighting. Mean annual recharge estimates varied from 112.7 ± 2.2 to 244.9 ± 12.4 mm/year, corresponding to approximately 6.5–14% of mean annual rainfall. Higher recharge values were obtained from baseflow separation and water-table fluctuation methods, reflecting strong seasonal groundwater responses. In contrast, soil-moisture balance and water-balance methods yielded lower estimates because they explicitly accounted for evapotranspiration and runoff losses. The chloride mass balance method produced intermediate values and represents longer-term effective recharge. Recharge was found to be highly seasonal and spatially heterogeneous, with highland areas acting as major recharge zones and lowland areas functioning mainly as discharge zones. Overall, convergence among multiple methods suggests a realistic recharge range of approximately 165–220.1 mm/year for the Fetam catchment. The study demonstrates that multi-method recharge assessment is essential in data-limited, seasonally dry basins and provides a scientific basis for sustainable groundwater development and drought-resilient water management.