Process consistency in models: The importance of system signatures, expert knowledge, and process complexity

M. Hrachowitz*, O. Fovet, L. Ruiz, T. Euser, S. Gharari, R. Nijzink, H. H G Savenije, C. Gascuel-Odoux, Jim Freer

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

116 Citations (Scopus)


Hydrological models frequently suffer from limited predictive power despite adequate calibration performances. This can indicate insufficient representations of the underlying processes. Thus, ways are sought to increase model consistency while satisfying the contrasting priorities of increased model complexity and limited equifinality. In this study, the value of a systematic use of hydrological signatures and expert knowledge for increasing model consistency was tested. It was found that a simple conceptual model, constrained by four calibration objective functions, was able to adequately reproduce the hydrograph in the calibration period. The model, however, could not reproduce a suite of hydrological signatures, indicating a lack of model consistency. Subsequently, testing 11 models, model complexity was increased in a stepwise way and counter-balanced by "prior constraints," inferred from expert knowledge to ensure a model which behaves well with respect to the modeler's perception of the system. We showed that, in spite of unchanged calibration performance, the most complex model setup exhibited increased performance in the independent test period and skill to better reproduce all tested signatures, indicating a better system representation. The results suggest that a model may be inadequate despite good performance with respect to multiple calibration objectives and that increasing model complexity, if counter-balanced by prior constraints, can significantly increase predictive performance of a model and its skill to reproduce hydrological signatures. The results strongly illustrate the need to balance automated model calibration with a more expert-knowledge-driven strategy of constraining models.

Original languageEnglish
Pages (from-to)7445-7469
Number of pages25
JournalWater Resources Research
Issue number9
Publication statusPublished - 2014


  • Complex models with prior constraints are consistent and robust
  • Expert-knowledge-based prior information has strong constraining power
  • Uncalibrated but constrained complex models outperform standard models


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