Highly Resolved Long-term 3D Hydrological Simulation of a Forested Catchment with Litter Layer and Fractured Bedrock

Abstract:

Soil water content plays a key role in the water and energy balance in soil, vegetation and atmosphere systems. According to Wood et al. (2011) there is a grand need to increase global-scale hyper-resolution water-energy-biogeochemistry land surface modelling capabilities. However, such a model scheme should also recognize the epistemic uncertainties, as well as the nonlinearity and hysteresis in its dynamics. Unfortunately, it is not clear how to parameterize hydrological processes as a function of scale and how to test deterministic models with regard to epistemic uncertainties. In this study, high resolution long-term simulations were conducted in the highly instrumented TERENO hydrological observatory, the Wüstebach catchment. Soil hydraulic parameters were derived using inverse modeling with the Hydrus-1D model using the global optimization scheme SCE-UA and soil moisture data from a wireless soil moisture sensor network. The estimated parameters were then used for 3D simulations using the integrated parallel simulation platform ParFlow-CLM. The simulated soil water content, as well as evapotranspiration and runoff, were compared with long-term field observations to illustrate how well the model was able to reproduce the water budget dynamics. With variable model setup scenarios in boundary conditions and anisotropy of hydraulic conductivity, we investigated how lateral flow processes above the underlying fractured bedrock affects the simulation results. Furthermore, we explored the importance of the litter layer and the heterogeneity of the forest soil in the simulation of flow processes and model performance. For the analysis of spatial patterns of simulated and observed soil water content we applied the method of empirical orthogonal function (EOF). The results suggest that strong anisotropy in the hydraulic conductivity may be the reason for the fast lateral flow observed in Wüstebach. Introduction of heterogeneity in the hydraulic properties in the hillslope and riparian zones improves estimates of soil water content and runoff, but has not significant impact on simulated actual evapotranspiration.