A Brief Analysis of Conceptual Model Structure Uncertainty Using 36 Models and 559 Catchments

W J M Knoben,M C Peel,K J A Fowler,R A Woods,J E Freer

doi:10.1029/2019wr025975

W J M Knoben, M C Peel + Show 3 more

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https://doi.org/10.1029/2019wr025975

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Abstract

AbstractThe choice of hydrological model structure, that is, 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.

Highlights

There is an ongoing debate in hydrology whether a “one model fits all” approach should be pursued, based on the assumption that the fundamental hydrological processes are the same everywhere (e.g., Fenicia et al, 2011; Linsley, 1982; Perrin et al, 2003; Savenije, 2009)
Results presented here are based on data for the KGE(Q) objective function obtained from the evaluation period, unless indicated as being calibration results or relating to one of the two other objective functions
80% of these benchmarks are obtained by using the mean calendar day flow, the remainder being obtained from the median calendar day flow (Figure 3b)

Summary

Introduction

There is an ongoing debate in hydrology whether a “one model fits all” approach should be pursued, based on the assumption that the fundamental hydrological processes are the same everywhere (e.g., Fenicia et al, 2011; Linsley, 1982; Perrin et al, 2003; Savenije, 2009) This assumption has led to development of rainfall runoff models that are designed to be applied across a wide range of catchments (see, e.g., discussion of the GR4J model in Fenicia et al, 2011, and consider more recent applications of this model in 142 catchments in the United States Oudin et al, 2018). Knowing how much uncertainty is associated with the choice of model structure is important for quantifying the reliability of model predictions (e.g., Biondi et al, 2012)

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