Improving the internal hydrological consistency of a process-based solute-transport model by simultaneous calibration of streamflow and stream concentrations

Abstract

Abstract. Improving the consistency of hydrological models, i.e. their ability to reproduce observed system dynamics, is required to increase their predictive power. As the use of streamflow data for calibration is necessary but not sufficient to constrain model and warrant model consistency, other strategies must be considered, in particular the use of additional data sources. The aim of this study is to test whether simultaneous calibration of dissolved organic carbon (DOC) and nitrate (NO3-) concentrations along with streamflow improves the hydrological consistency of a parsimonious solute-transport model. A multi-objective and multi-variable approach was used to evaluate the model in an intensive agricultural headwater catchment. Our results showed that using daily stream concentrations of DOC and NO3- together with streamflow data during calibration did not improve the model's ability to accurately predict streamflow for calibration or evaluation periods. However, the internal consistency of the model was improved for the simulation of low flows, groundwater storage and upstream soil storage, but not for the simulation of riparian soil storage. Parameter uncertainty decreased when the model was calibrated using solute concentrations, except for parameters related to fast and slow reservoir flow. This study shows the added value of using multiple data sources in addition to streamflow data for calibration, in particular DOC and NO3- concentrations, to constrain hydrological models for a better representation of internal hydrological states and flow. With the increasing availability of solute data from catchment monitoring, this approach provides an objective way to improve the internal consistency of hydrological models that can be used with confidence in scenario evaluation.