Evaluating explicit and implicit routing for watershed hydro‐ecological models of forest hydrology at the small catchment scale

Abstract

Abstract:This paper explores the behaviour and sensitivity of a watershed model used for simulating lateral soil water redistribution and runoff production. In applications such as modelling the effects of land-use change in small headwater catchments, interactions between soil moisture, runoff and ecological processes are important. Because climate, soil and canopy characteristics are spatially variable, both the pattern of soil moisture and the associated outflow must be represented in modelling these processes. This study compares implicit and explicit routing approaches to modelling the evolution of soil moisture pattern and spatially variable runoff production. It also addresses the implications of using different landscape partitioning strategies. This study presents the results of calibration and application of these different routing and landscape partitioning approaches on a 60 ha forested watershed in Western Oregon. For comparison, the different approaches are incorporated into a physically based hydro-ecological model, RHESSys, and the resulting simulated soil moisture, runoff production and sensitivity to unbiased error are examined. Results illustrate that both routing approaches can be calibrated to achieve a reasonable fit between observed and modelled outflow. Calibrated values for effective watershed hydraulic conductivity are higher for the explicit routing approach, which illustrates differences between the two routing approaches in their representation of internal watershed dynamics. The explicit approach illustrates a seasonal shift in drainage organization from watershed to more local control as climate goes from a winter wet to a summer dry period. Assumptions used in the implicit approach maintain the same pattern of drainage organization throughout the season. The implicit approach is also more sensitive to random error in soil and topographic input information, particularly during wetter periods. Comparison between the two routing approaches illustrates the advantage of the explicit routing approach, although the loss of computational efficiency associated with the explicit routing approach is noted. To compare different strategies for partitioning the landscape, the use of a non-grid-based method of partitioning is introduced and shown to be comparable to grid-based partitioning in terms of simulated soil moisture and runoff production.

Maximum entropy production: can it be used to constrain conceptual hydrological models?

“…For a detailed description of the watershed the reader is referred to e.g. Rothacher (1965); Rothacher et al (1967) or Tague and Band (2001). Here we give only a short description.…”

“…The catchment is completely forested, primarily by mature Douglas fir. The underlying bedrock is volcanic material from the Oligocene to lower Miocene which is overlain by a thick layer of weathered, unconsolidated material of generally high porosity (∼ 0.6) and hydraulic conductivity (∼ 90 m day −1 ) (Tague and Band, 2001).…”

An approach to understanding hydrologic connectivity on the hillslope and the implications for nutrient transport

“…Both within the TOPMODEL hydrologic framework and using more explicitly based models, others have attempted to deal with the question of the impacts that landscape spatial heterogeneity within a watershed (e.g., soil transmissivity, soil depth, vegetation) have on hydrologic [Beven and Freer, 2001;Calver and Wood, 1991;Kirkby, 1998;Watson et al, 1998;Wigmosta et al, 1994;Wigmosta and Lettenmaier, 1999;Tague and Band, 2001] and biogeochemical transport [Band et al, 2001]. What we have attempted to do in this paper is to use a simple parameterization of DTB as a means for exploring and understanding hydrologic connectivity and the implications this has on downslope nutrient transport.…”

“…The work presented here is a step toward developing such a linked, process-based model. It is notable that there are very few (if any) applications of mechanistic models that can predict the outflow of materials as a function of processes and interactions within the catchment [Cosby et al, 1985;Hornberger et al, 1994;Fisher et al, 2000;Lee et al, 2000;Band et al, 2001].…”

Representation of landscape variability and lateral redistribution processes for large-scale hydrological modelling in semi-arid areas

“…(A3)). Comparable formulations for more complex geometric settings have been used by Wigmosta et al (1994) and Tague and Band (2001). The hydraulic gradient is given by the slope gradient s TC of the terrain component.…”