Cornelissen, Thomas Daniel: 3D-Modeling of unsaturated flow dynamics and pattern : Potentials and Limitations at different spatial and temporal scales. - Bonn, 2016. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
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author = {{Thomas Daniel Cornelissen}},
title = {3D-Modeling of unsaturated flow dynamics and pattern : Potentials and Limitations at different spatial and temporal scales},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2016,
month = jun,

note = {The aim of this thesis was to evaluate the suitability of the physically based, distributed 3D hydrological model HydroGeoSphere for the simulation of spatio-temporal soil moisture variability as well as unsaturated flow processes and to investigate the models’ applicability at large spatial and temporal scales.
To achieve these aims, hydrological simulations of a forested headwater catchment in the Eifel region were used to evaluate the suitability of the model. The headwater catchment offered not only site specific measurement of discharge, evapotranspiration and interception, but the instrumentation in the catchment also provided the unique possibility to compare simulated to continuously measured soil moisture variability for two years. As model results heavily depend on the chosen spatial and temporal model resolution, the catchment was simulated at 2 different spatial and 2 different temporal discretizations.
All simulations showed a satisfactory agreement to annual water balance components and discharge dynamics. A dominance of subsurface flow was also simulated for every simulation which corresponds to previous findings in forested catchments. The quality of simulated soil moisture variability exhibited large variations between the temporal dynamics and spatial patterns. Dynamics were well simulated, but the simulation missed short term variations probably due to a lack of bypass flow in the model structure. On the contrary, simulated and measured soil moisture patterns showed large differences indicating a simplified representation of spatial heterogeneity in the model. Simulation of flow processes and water balance components only showed a weak sensitivity to spatial or temporal resolution while higher spatial resolution was identified as an important factor in the successful simulation of soil moisture patterns.
The potential of using the model at larger spatial and temporal scales was tested with simulations at a mesoscale catchment including the above described headwater catchment. The challenge of simulating large catchments refers to the incorporation of spatial variability in climate and land use, especially the land use specific parameter estimation. With a step-wise introduction of spatial heterogeneity in soil, land use, potential evapotranspiration and precipitation into the simulation, the precipitation pattern was identified as the most and the potential evapotranspiration pattern as the least important for discharge simulation.
The land use specific parameter estimation was done by transferring calibrated evapotranspiration parameters from the headwater catchment to the land use of the mesoscale catchment. This method results in very good agreement of annual and monthly simulated actual evapotranspiration rates to measured data and literature values. Thus, this thesis introduced the transfer of model parameters from smaller to larger catchment as a promising method of parameter estimation of large catchments.
Additional model validation was performed with a 50 years simulation run of forest growth for the mesoscale catchment. Results showed that the model is able to maintain a balance between inputs (precipitation) and outputs (discharge, evapotranspiration) over several decades and that it provides reasonable simulation of discharge dynamics for this time period.},

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