Transit Time Estimation in Catchments: Recent Developments and Future Directions

Water transit time is now a standard measure in catchment hydrological and ecohydrological research. The last comprehensive review of transit time modeling approaches was published 15+ years ago. But since then the field has largely expanded with new data, theory and applications. Here, we review these new developments with focus on water-age-balance approaches and data-based approaches. We discuss and compare methods including StorAge-Selection functions, well/partially mixed compartments, water age tracking through spatially distributed models, direct transit time estimates from controlled experiments, young water fractions, and ensemble hydrograph separation. We unify some of the heterogeneity in the literature that has crept in with these many new approaches, in an attempt to clarify the key differences and similarities among them. Finally, we point to open questions in transit time research, including what we still need from theory, models, field work, and community practice.

Automated summary

This study reviews the recent developments in water transit time research, focusing on water-age-balance approaches and data-based approaches. Various methods, including StorAge-Selection functions, well/partially mixed compartments, and direct transit time estimates, are discussed and compared. The study aims to unify the heterogeneity in the literature and highlight the remaining open questions in transit time research.