Abstract
Abstract. This study explores the suitability of a single hillslope as a parsimonious representation of a catchment in a physically based model. We test this hypothesis by picturing two distinctly different catchments in perceptual models and translating these pictures into parametric setups of 2-D physically based hillslope models. The model parametrizations are based on a comprehensive field data set, expert knowledge and process-based reasoning. Evaluation against streamflow data highlights that both models predicted the annual pattern of streamflow generation as well as the hydrographs acceptably. However, a look beyond performance measures revealed deficiencies in streamflow simulations during the summer season and during individual rainfall–runoff events as well as a mismatch between observed and simulated soil water dynamics. Some of these shortcomings can be related to our perception of the systems and to the chosen hydrological model, while others point to limitations of the representative hillslope concept itself. Nevertheless, our results confirm that representative hillslope models are a suitable tool to assess the importance of different data sources as well as to challenge our perception of the dominant hydrological processes we want to represent therein. Consequently, these models are a promising step forward in the search for the optimal representation of catchments in physically based models.
Highlights
The value of physically based hydrological models has been doubted (e.g., Beven, 1989; Savenije and Hrachowitz, 2016) since their idea was introduced by Freeze and Harlan (1969)
In contrast to what we found for the Colpach, the ensemble of simulated soil moisture at 10 cm for the Wollefsbach falls into the state space spanned by the observations; it only slightly underestimates the rolling median of the observed soil moisture (Fig. 11c)
From the fact that streamflow simulations were acceptable in both catchments when being judged solely on model efficiency criteria, one could conclude that the hillslopes portray the dominant structures and processes which control the runoff generation in both catchments well
Summary
The value of physically based hydrological models has been doubted (e.g., Beven, 1989; Savenije and Hrachowitz, 2016) since their idea was introduced by Freeze and Harlan (1969). Based models like MikeShe (Refsgaard and Storm, 1995) or CATHY (Camporese et al, 2010) typically rely on the Darcy–Richards concept for soil water dynamics, the Penman–Monteith equation for soil– vegetation–atmosphere exchange processes and hydraulic approaches for overland flow and streamflow. Each of these concepts is subject to limitations arising from our imperfect understanding of the related processes and is afflicted by the restricted transferability of process descriptions from idealized laboratory conditions to heterogeneous natural systems (Grayson et al, 1992; Gupta et al, 2012). These and other studies (e.g., Ebel et al, 2008; Scudeler et al, 2016) show that physically based models can be set up using a mix of expert knowledge and observed parameters and may be tested
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