In recent years, large-scale hydrological models have been increasingly used at regional and global scales to support decision making. Their realism in simulating water balance components is crucial for building trust across different use cases. Hydrological models may reproduce streamflow well but misrepresent other fluxes, due to internal fluxes compensations and equifinality. Alternative setups, such as the choice of input data, model structure, and calibration methods, can influence how water is partitioned across model states and fluxes. Modellers can adjust these choices to improve the representation of the water-balance components most relevant for a given application, even when this comes at some cost to overall streamflow performance. “Hydrological auditing” of models, i.e. a thorough critical review of their realism beyond the calibration targets (usually streamflow), provides useful insights for both practical applications and process understanding. We present one such exercise in a representative European case study using a physically based hydrological model (LISFLOOD), as calibrated and set up for the European Flood Awareness System (EFAS). Originally developed for flood forecasting, LISFLOOD is increasingly also employed for drought monitoring and water resources management. We evaluate LISFLOOD v4.1.1's performance in simulating streamflow, evapotranspiration, and overall water balance in the Po River Basin, a complex and highly managed basin in Northern Italy. Six alternative model setups are tested, including different soil layers depths and preferential flow representations. Results show that the model setup currently used in EFAS v.5.0 performs best in terms of streamflow simulation, particularly at the daily time step, but tends to underestimate evapotranspiration. In turn, this may lead to an overestimation of groundwater recharge and a poor water balance representation. The use of the Budyko framework as a diagnostic tool reveals that model setups without preferential flow better match the expected long-term water balance, but reduce daily streamflow performance. The study highlights the importance of evaluating model performance and auditing alternative parametrizations to ensure accurate simulations of water balance components, crucial for water resources management. We propose diagnostic criteria to support the evaluation of physically based distributed models, across different applications, while preserving consistency in the representation of long-term water-balance components. Finally, we argue that such hydrological auditing becomes increasingly relevant as the added value of physically based models, compared to increasingly competitive data-driven models, lies in their ability to provide diagnostically useful and physically-consistent representations of internal water-balance processes.

MOSCHINI Francesca;  FICCHI Andrea;  PISTOCCHI Alberto; 

2025-12-16

COPERNICUS GESELLSCHAFT MBH

JRC145087

1991-9603 (online),   

https://gmd.copernicus.org/articles/19/7855/2026/,    https://publications.jrc.ec.europa.eu/repository/handle/JRC145087,   

10.5194/gmd-19-7855-2026 (online),