A brief analysis of conceptual model structure uncertainty using 36 models and 559 catchments

Wouter J M Knoben*, Jim E Freer, Murray Peel, K J A Fowler, Ross A Woods

*Corresponding author for this work

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

70 Citations (Scopus)
72 Downloads (Pure)


The choice of hydrological model structure, i.e. a model’s selection of states and fluxes and the equations used to describe them, strongly controls model performance and realism. This work investigates differences in performance of 36 lumped conceptual model structures calibrated to and evaluated on daily streamflow data in 559 catchments across the United States. Model performance is compared against a benchmark that accounts for the seasonality of flows in each catchment. We find that our model ensemble struggles to beat the benchmark in snow-dominated catchments. In most other catchments model structure equifinality (i.e. cases where different models achieve similar high efficiency scores) can be very high. We find no relation between the number of model parameters and performance during either calibration or evaluation periods, nor evidence of increased risk of overfitting for models with more parameters. Instead, the choice of model parametrization (i.e. which equations are used and how parameters are used within them) dictates the model’s strengths and weaknesses. Results suggest that certain model structures are inherently better suited for certain objective functions and thus for certain study purposes. We find no clear relationships between the catchments where any model performs well and descriptors of those catchments’ geology, topography, soil and vegetation characteristics. Instead, model suitability seems to relate strongest to the streamflow regime each catchment generates and we have formulated several tentative hypotheses that relate commonalities in model structure to similarities in model performance. Modeling results are made publicly available for further investigation.
Original languageEnglish
Article numbere2019WR025975
Number of pages23
JournalWater Resources Research
Issue number9
Publication statusPublished - 3 Sept 2020

Structured keywords

  • Water and Environmental Engineering


  • conceptual model comparison
  • model structure uncertainty
  • catchment modeling


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  • Water Resources Research Editors' Choice Award

    Knoben, Wouter J M (Recipient), Freer, Jim E (Recipient), Peel, Muray (Recipient), Fowler, Keirnan (Recipient) & Woods, Ross A (Recipient), 14 Dec 2021

    Prize: Prizes, Medals, Awards and Grants

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