Characterizing and reducing equifinality by constraining a distributed catchment model with regional signatures, local observations, and process understanding

Abstract

Abstract. Distributed catchment models are widely used tools for predicting hydrologic behavior. While distributed models require many parameters to describe a system, they are expected to simulate behavior that is more consistent with observed processes. However, obtaining a single set of acceptable parameters can be problematic, as parameter equifinality often results in several "behavioral" sets that fit observations (typically streamflow). In this study, we investigate the extent to which equifinality impacts a typical distributed modeling application. We outline a hierarchical approach to reduce the number of behavioral sets based on regional, observation-driven, and expert-knowledge-based constraints. For our application, we explore how each of these constraint classes reduced the number of "behavioral" parameter sets and altered distributions of spatiotemporal simulations, simulating a well-studied headwater catchment, Stringer Creek, Montana, using the distributed hydrology-soil-vegetation model (DHSVM). As a demonstrative exercise, we investigated model performance across 10 000 parameter sets. Constraints on regional signatures, the hydrograph, and two internal measurements of snow water equivalent time series reduced the number of behavioral parameter sets but still left a small number with similar goodness of fit. This subset was ultimately further reduced by incorporating pattern expectations of groundwater table depth across the catchment. Our results suggest that utilizing a hierarchical approach based on regional datasets, observations, and expert knowledge to identify behavioral parameter sets can reduce equifinality and bolster more careful application and simulation of spatiotemporal processes via distributed modeling at the catchment scale.

Ecohydrological modelling with EcH2O‐iso to quantify forest and grassland effects on water partitioning and flux ages

“…Ecohydrologic models tend to be highly parameterized, and the opportunity for insight only exists if a limited number of feasible and consistent model configurations can be identified. Multicriteria calibration and verification of such models can increase the confidence that the dominant ecohydrological processes are being appropriately represented in different landscape compartments and accurately quantified (Kelleher et al, ; Kuppel et al, ). Model failure to adequately represent observed processes also provides an opportunity to learn and improve conceptualization (Birkel, Soulsby, & Tetzlaff, ; Dunn et al, ).…”

“…We also used various known quantitative thresholds as “observation‐driven and expert‐knowledge‐based constraints” (Kelleher, McGlynn, & Wagener, ; Table ). For example, previous water balance studies of Lake Stechlin (e.g., Pöschke et al, ) have estimated that the annual average groundwater recharge over the catchment (15 km 2 ) ranges between 65 and 150 mm year −1 , which is mainly covered by separate or mixed stands of beech and pine (97%; CORINE Land Cover database CLC 2012).…”

Landscape analysis of soil methane flux across complex terrain

“…We utilized understanding of watershed hydrology processes at TCEF (Jencso et al, 2009Kelleher et al, 2017;Nippgen et al, 2015) to design a sampling campaign which captured CH 4 fluxes across environmental gradients that were characterized through topographic analysis, field observation, and hydrological measurements. This approach allowed us to assess environmental influences on CH 4 fluxes: at the point scale, we examined the influence of environmental variables on observed CH 4 fluxes (f CH 4 ); at the intermediate scale, we identified functional landscape elements (riparian, upland, and the transition between them) which related to the direction and persistence of f CH 4 ; and at the landscape scale, we assessed the influence of topographic position on cumulative CH 4 fluxes (ln|F CH 4 | in ) in the uplands.…”

Landscape analysis of soil methane flux across complex terrain

“…We utilized understanding of watershed hydrology processes at TCEF (Jencso et al, 2009;Jencso et al, 2010;Kelleher et al, 2017;Nippgen et al, 2015) to design a sampling campaign which captured CH4 fluxes across environmental gradients that were characterized through topographic analysis, field observation, and hydrological measurements. This approach allowed us to assess environmental influences on CH4 fluxes; at the point scale, we examined the influence of environmental variables 5 on observed CH4 fluxes (fCH4), at the intermediate scale, we identified functional landscape elements (riparian, upland, and the transition between them) which related to the direction and persistence of fCH4, and at the landscape scale, we assessed the influence of topographic position on cumulative CH4 fluxes (ln|FCH4|in) in the uplands.…”