Exploring the Critical Zone Heterogeneity and the Hydrological Diversity Using an Integrated Ecohydrological Model in Three Contrasted Long‐Term Observatories

• Published in: Water resources research Vol. 59; no. 12
• Main Authors: Ackerer, J., Kuppel, S., Braud, I., Pasquet, S., Fovet, O., Probst, A., Pierret, M. C., Ruiz, L., Tallec, T., Lesparre, N., Weill, S., Flechard, C., Probst, J. L., Marçais, J., Riviere, A., Habets, F., Anquetin, S., Gaillardet, J.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01-12-2023; American Geophysical Union
• Subjects: Agricultural land; Agricultural practices; Agricultural watersheds; Aquifers; Ecohydrology; Environmental Sciences; Evapotranspiration; Geological history; Geology; Geomorphology; Geophysics; Heterogeneity; Hydrologic cycle; Hydrological cycle; Hydrology; Landscape; Local climates; Mathematical models; Meteorology; Modelling; Mountain forests; Numerical models; Observatories; Precipitation patterns; Regolith; River flow; Rivers; Satellite imagery; Schist; Schists; Sciences of the Universe; Slopes; Soil sciences; Soil water storage; Stream water; Tectonics; Transit time; Vegetation; Water; Water availability; Water storage; France; Strengbach watershed; Auradé catchment; Critical Zone Observatories Network; Naizin watershed; ecohydrological modelling; long term observations
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2023WR035672

An integrated ecohydrological modeling approach was deployed in three long‐term critical zone (CZ) observatories of the French CZ network (CZ Observatories—Application and Research) to better understand how the CZ heterogeneity modulates the water cycle within territories. Ecohydrological simulations with the physically based model EcH
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O‐iso constrained by a wide range of observations crossing several disciplines (meteorology, hydrology, geomorphology, geophysics, soil sciences, and satellite imagery) are able to capture stream water discharges, evapotranspiration fluxes, and piezometric levels in the Naizin, Auradé, and Strengbach watersheds. In Naizin, an agricultural watershed in northwestern France with a schist bedrock underlying deep weathered materials (5–15 m) along gentle slopes, modeling results reveal a deep aquifer with a large total water storage (1,080–1,150 mm), an important fraction of inactive water storage (94%), and relatively long stream water transit times (0.5–2.5 years). In the Auradé watershed, representative of agricultural landscapes of the southwestern France developed on molasse, a relatively shallow regolith (1–8 m) is observed along hilly slopes. Simulations indicate a shallow aquifer with moderate total water storage (590–630 mm), an important fraction of inactive water storage (91%), and shorter stream water transit times (0.1–1.3 years). In the Strengbach watershed, typical of mid‐mountain forested landscapes developed on granite, CZ evolution implies a shallow regolith (1–5 m) along steep slopes. Modeling results infer a shallow aquifer with the smallest total water storage (475–575 mm), the shortest stream water transit times (0.1–0.7 years), but also the highest fraction of active water storage (18%).
Understanding how water is stored and released in landscapes is essential for predicting water availability in a changing world. It is of course driven by the local climate, but also by the landscape settings, from the vegetation to the belowground structure inherited from the geological history. In three intensively studied observatories across France, we used numerous field measurements and a numerical model of water‐vegetation‐subsurface interactions to better depict how differences between landscapes shape the water cycle. We found that the geological history determines how much water is stored in watersheds, through the thickness of water‐holding rocks and soils. How this storage contributes to surface processes (including river flow) is modulated by more recent changes, from valley morphology and tectonics to agricultural practices and precipitation patterns. This study highlights that considering the continuity between long and short‐term landscape processes is key to a detailed understanding of the water cycle.
The long‐term critical zone (CZ) evolution controlling the regolith thickness strongly impacts the total water storage in watersheds, while the Quaternary geomorphological evolution influences the current hydrological partitioning and the separation of hydrologically active and inactive water storage
Both internal watershed characteristics and external forcings, such as current atmospheric forcing and recent land use need to be considered to infer stream persistence and to understand hydrological diversity
The observed hydrological diversity cannot be fully understood without considering a continuum of time scales in CZ evolution