6. Workshop Alpine Hydrologie

Hydrological model calibration is commonly based on objective functions that emphasize specific segments of the discharge distribution, often resulting in models that perform well for either low, medium, or high flows, but rarely across the full hydrological spectrum. This study presents a flexible calibration framework that enables targeted representation of diverse flow regimes through the use of the Bregman and Generalized Piecewise Linear families of scoring functions. By appropriately selecting the scoring function for each targeted objective, model calibration can be directed toward specific regimes while preserving a coherent and unified estimation framework.

The methodology is applied to the Upper Adige River Basin, a large Alpine catchment characterized by complex topography, strong climatic gradients, and a hydrological regime influenced by both snowmelt and intense precipitation events. A distributed hydrological model is calibrated using alternative scoring functions designed to progressively emphasize low, intermediate, and high flows. Model performance is assessed using regime-specific diagnostics and conventional hydrological performance metrics.

Results demonstrate that the proposed framework effectively improves the representation of targeted flow regimes while maintaining satisfactory performance over the entire flow distribution. In particular, calibrations emphasizing high-flow regimes provide more accurate simulations of flood peaks, whereas calibrations focused on low-flow regimes enhance the representation of drought and water availability conditions. Intermediate formulations achieve a balanced performance across multiple flow regimes, highlighting the ability of the framework to explicitly control calibration trade-offs.

The proposed approach provides a general, flexible, and computationally efficient methodology for multi-purpose hydrological model calibration. Its ability to tailor model performance to specific hydrological objectives makes it particularly suitable for applications in flood risk assessment, drought management, water resources planning, and climate change impact studies.