Tracer-aided ecohydrological modelling to quantify hydrologic partitioning and investigate partitioning processes

Hydrological partitioning, the separation of precipitation into different hydrological fluxes, remains poorly constrained in forested prealpine catchments. Here, we apply EcH₂O-iso, a distributed process-based tracer-aided ecohydrological model, to investigate hydrological partitioning in the WaldLab forest research site in Zurich, Switzerland. EcH₂O-iso simulates water and energy fluxes while tracking stable water isotopes across all compartments of the critical zone. EcH₂O-iso was calibrated and validated with five years of hydrometric measurements, along with high-frequency observations of stable water isotope ratios in precipitation, streams, groundwater, xylem, and bulk and mobile soil water. Our results highlight the importance of explicitly representing dual-porosity soil water storage dynamics in models, providing insights into how mobile and immobile soil water storages are partitioned differently. These results were compared with previous findings at the WaldLab, particularly the seasonal dynamics of interception, infiltration, and plant water uptake. Future work will use these results alongside simulations in other snow-dominated alpine and boreal catchments to contrast ecohydrological processes between snow- vs rain-dominated ecosystems.