From multi-source data uncertainty to interval-based robust calibration: A transferable solution for hydrological modeling in data-scarce alpine basins

Study Region The European Alps feature steep elevation gradients, snow-influenced hydrology, and strong spatial variability in water and energy fluxes. Hydrological modeling is limited by sparse high-elevation observations, while growing multi-source data availability introduces inter-product uncertainty. The Adige River Basin, Italy, was selected to evaluate calibration under these conditions. Study Focus We developed interval-based robust calibration (IROC), which uses multiple evapotranspiration (ET) products as observational bounds rather than selecting a single reference. IROC combines interval consistency, controlling average and upper-tail departures, with interval plausibility, identifying parameter sets supported across subbasins and calibration–validation periods. Implemented with SWAT using MOD16, GLEAM, ERA5-Land, and PML, IROC was compared with four single-reference calibrations. Temporal validation used the four-product ET envelope, while hydrological performance was independently evaluated against observed discharge at Trento. New Hydrological Insights for the Region IROC identified consensus parameter sets that maintained monthly ET within multi-product bounds across subbasins and uncertainty levels. Single-reference calibrations favored different parameter combinations and produced distinct discharge responses, demonstrating reference-dependent parameter inference and prediction. Although IROC did not minimize every discharge metric, it balanced multi-product ET consistency, temporal robustness, central discharge accuracy, and retained ensemble compactness. Overall, IROC reduces reliance on an unverifiable single reference and offers a transferable calibration strategy for integrating multiple uncertain datasets in data-scarce or ungauged basins.