Critical Zone Response Times and Water Age Relationships Under Variable Catchment Wetness States: Insights Using a Tracer-Aided Ecohydrological Model

Aaron A. Smith*, Doerthe Tetzlaff, Marco Maneta, Chris Soulsby

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


The dynamic relationships between water flux and storage, together with the associated water ages and speed of hydrological responses (as proxies for velocity and celerity respectively) are fundamental to understanding how catchments react to hydroclimate perturbations, such as floods and droughts. Using results from a calibrated, tracer-aided ecohydrological model (EcH2O-iso) we analyzed the dynamics of storage-flux-age-response time (RT) interactions at scales that resolve the internal heterogeneity of these non-stationary relationships. EcH2O-iso has previously shown an adequate representation of ecohydrological flux partitioning and storage dynamics (celerity), and water ages (velocity) over 11-year at Demnitzer Millcreek catchment (DMC, 66 km2), a drought-sensitive, lowland catchment in Germany. The 11-year period had marked hydroclimatic contrasts facilitating the evaluation of flux-storage-age-RT dynamics under different wetness anomalies. Our results show that the spatio–temporal variability of soil moisture and ecohydrological partitioning dynamics reflect both land use (especially forest cover) and distinct soil units (i.e., brown earth vs. podzolic soils). Spatial differences in RTs of storage were driven by rapid soil evaporation and transpiration responses to rainfall, which revealed a divergence of transpiration ages from RTs. RTs of groundwater and streamflow were fast (days), but mediation by soil water storage dynamics caused marked separation from water ages (years-decades) of deeper flow paths. Analysis of RTs and ages revealed a degradation of process representation with coarsening model spatial resolution. This study uses novel analysis of the spatio-temporal interactions of flux-storage-age-RT from a model to understand the sensitivity and resilience of catchment functionality to hydroclimatic perturbations.

Original languageEnglish
Article numbere2021WR030584
Number of pages21
JournalWater Resources Research
Issue number4
Early online date26 Apr 2022
Publication statusPublished - Apr 2022

Bibliographical note

Funding Information:
The authors acknowledge funding from the European Research Council (Grant No. GA 335910 VeWa). Contributions from CS were supported by the Leverhulme Trust through the ISO-LAND project (Grant No. RPG 2018 375). Isotopic analysis was conducted by David Dubbert at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries. The authors acknowledge the University of Aberdeen IT services for the use of the high-performance computing (HPC cluster), which was used for all model runs. Funding for DT was also received through the Einstein Research Unit “Climate and Water under Change” from the Einstein Foundation Berlin and Berlin University Alliance.

Publisher Copyright:
© 2022. The Authors.


  • ecohydrological modelling
  • hydrologic response times
  • model scaling
  • water age


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