Defining archetypal transit time distributions and their dynamics in real-world catchments

• Applicant: Ingo Heidbüchel, Ph.D.
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 454619223

The management of water resources is complicated, in particular when dealing with the prediction of solute export from entire catchments. Substances that are naturally or anthropogenically introduced into the hydrologic cycle are hard to trace along their way through soil, vegetation and bedrock. Only at the catchment outlet they become more easily measureable again as an integrated signal. One common approach to predict the export of solutes is to set up physically-based, distributed hydrologic models for specific catchments, to calibrate them with recorded time series of precipitation and discharge and thus to simulate in detail every aspect of solute transport in the catchments. However, the setup of such models is relatively laborious and the application often computationally expensive. Also, the results are usually not directly transferable to other catchments. The goal I pursue with this proposal is to facilitate a simpler approach for the prediction of solute export by using physically-based models to integrate more realism into conceptual models at the catchment scale. I would like to achieve this by linking the shape of transfer functions (which are used in many conceptual models to convert solute input into solute output) with physically measureable catchment and climate parameters. These transfer functions are forward transit time distributions that contain detailed information on how long waters and substances entering with a particular precipitation event stay inside of a catchment before they discharge. The shape of transit time distributions changes depending on which flow paths are preferentially activated during and after a precipitation event. The shape also varies spatially with specific catchment characteristics like, for example, soil depth or hydraulic conductivity. In a virtual experiment in a study that forms the basis of this proposal I used a physically-based, distributed model (HydroGeoSphere) to examine how the shape of transit time distributions changes spatially between catchments with different properties and how it changes temporally within one catchment with changing antecedent moisture content. Now I aim for the verification of the results of the virtual modeling study with the help of empirical field data in real-world catchments. To this end I am going to use discharge and nitrate time series of the freely accessible data base Germany, select, set up and calibrate six uniquely representative (archetypal) catchments in HydroGeoSphere and compare the resulting transit time distributions with the ones I produced with the virtual catchments.

• DFG Programme: Research Grants