High spatial heterogeneity of catchment properties enhances the variability of ecohydrological responses to changing natural and anthropogenic conditions, like the European-wide droughts in 2018–2019. Based on new adaptations of a tracer-aided, process-based ecohydrological model (EcH2O-iso), we investigated drought-induced nonstationary ecohydrological behavior in a small agricultural headwater catchment (1.44 km2) in central Germany. Multiple environmental time-series helped inform various aspects of catchment functioning that have been impacted by agricultural activity and changing climate conditions and helped to further constrain model calibration. Multi-criteria calibration showed that data collected during drought years were highly informative in reproducing the changes in stream water dynamics. Further, inclusion of (Formula presented.) and (Formula presented.) data was valuable for reducing model uncertainty and increasing confidence in simulations of green- and blue-water flux partitioning and storage-flux-age interactions. Using the best-performing calibrations, we further analyzed the high spatiotemporal variability of internal ecohydrological processes and the varying responses of fluxes and associated water ages to prolonged drought stress. Under drought conditions, modeled stream runoff contributed from deeper, older storages increased significantly after a particularly wet season, resulting in a sharp increase in stream water age. Unlike relatively minor changes in soil evaporation, seasonally typical transpiration fluxes were initially maintained in April–June but dramatically decreased as the drought further developed in July–September. Importantly, the tracer-based transpired water age was much older after April, providing a potential indicator of drought impacts and the need for precautionary management responses. Our findings are important for similar agricultural headwater ecosystems in other drought-sensitive regions.
Data used in this study are obtained from the Terrestrial Environmental Observatories (TERENO) project and the Modular Observation Solutions for Earth Systems (MOSES) project, both initiated and funded under the Earth and Environment Program of the Helmholtz Association, Germany. The authors highly appreciate efforts of all partners involved in different monitoring activities. Specifically, The authors would like to thank Frido Reinstorf and Florian Pöhlein from University of Applied Sciences Magdeburg‐Stendal for sharing the hydroclimatic and groundwater level data; Kay Knöller, Ralf Merz and Christin Müller, from Department of Catchment Hydrology (UFZ), for sharing the data of stable isotopes of water and for the constructive discussions; Hans‐Jörg Vogel, Holger Rupp and Ralf Gründling, from Department of Soil System Science (UFZ), for sharing the lysimeter soil moisture data. The authors thank the Editor, the Associate Editor, and three reviewers (Trish Stadnyk and two anonymous reviewers) for their constructive comments. The data are presented in the tables, figures, and supplements. The authors would like to thank Marco Maneta for his support and discussion on the modeling. Contributions from C. Soulsby were supported by the Leverhulme Trust's ISOLAND project.
- drought stress
- ecohydrological functioning
- multi-criteria calibration
- stable isotopes of water and water ages
- tile drainage
- tracer-aided modeling