Spatiotemporal Dynamics of Active Root Zone Storage Revealed From Hybrid Machine Learning
14 affiliations
- 1Biogeochemical Integration Max Planck Institute for Biogeochemistry Jena Germany
- 2Department of Geography Friedrich Schiller University Jena Jena Germany
- 3ELLIS Unit Jena Jena Germany
- 4Max-Planck-Institut fur Biogeochemie
- 5Friedrich-Schiller-Universitat Jena
- 6European Commission Joint Research Centre (JRC) Ispra Italy
- 7European Commission, Joint Research Center (JRC)
- 8School of Geography and the Environment University of Oxford Oxford UK
- 9University of Oxford
- 10School of Environment, Beijing Normal University
- 11UFZ‐Helmholtz Centre for Environmental Research Leipzig Germany
- 12Helmholtz-Zentrum fur Umweltforschung UFZ
- 13School of Environmental Science and Engineering Southern University of Science and Technology Shenzhen China
- 14Southern University of Science and Technology
Abstract
Water within the root zone regulates water, energy, and carbon exchanges at the land‐atmosphere interface, yet the dynamically active portion of subsurface water that ecosystems mobilize for evapotranspiration (ET) remains unclear, because it represents only part of the total subsurface storage. To address this gap, we develop a catchment‐scale, ecosystem‐oriented hybrid machine learning model that integrates a parsimonious ecohydrological structure with data‐driven flexibility to infer time‐varying active root zone storage (a S rz ) as a latent state variable. Without prescribing rooting depth or soil layers, the model learns adaptive water partitioning from multi‐source observations of ET, runoff, snow, and terrestrial water storage, enabling diagnosis of both dynamic a S rz and its realized capacity. Applied across hundreds of U.S. catchments over the period 2001–2020, the framework reveals coherent spatial and hydroclimatic patterns, with a S rz peaking in transitional regions where atmospheric demand and water supply are balanced. The realized capacity reflects how belowground water access varies with long‐term hydroclimatic and substrate constraints. We further show that defining storage as a realized quantity through system dynamics improves stability and interpretability under varying observational and structural conditions. Overall, this study demonstrates how hybrid modeling can be used to diagnose ecosystem‐accessible water storage as a latent state, providing a physically consistent and observation‐informed pathway to quantify belowground processes that remain inaccessible to direct measurement and control key land‐atmosphere interactions.
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BibTeX
@article{blougouras2026spatiotemporal,
title = {{Spatiotemporal Dynamics of Active Root Zone Storage Revealed From Hybrid Machine Learning}},
author = {Georgios Blougouras and Shijie Jiang and Alexander Brenning and Mirco Migliavacca and Louise J. Slater and Jialiang Zhou and Rohini Kumar and Lu Tian and Chao Wang and Markus Reichstein},
journal = {Water Resources Research},
year = {2026},
month = oct,
doi = {10.1029/2025wr042803},
url = {https://doi.org/10.1029/2025wr042803},
note = {CC BY},
}
RIS
TY - JOUR
TI - Spatiotemporal Dynamics of Active Root Zone Storage Revealed From Hybrid Machine Learning
AU - Georgios Blougouras
AU - Shijie Jiang
AU - Alexander Brenning
AU - Mirco Migliavacca
AU - Louise J. Slater
AU - Jialiang Zhou
AU - Rohini Kumar
AU - Lu Tian
AU - Chao Wang
AU - Markus Reichstein
PY - 2026
DA - 2026/10/01
JO - Water Resources Research
DO - 10.1029/2025wr042803
UR - https://doi.org/10.1029/2025wr042803
AB - Water within the root zone regulates water, energy, and carbon exchanges at the land‐atmosphere interface, yet the dynamically active portion of subsurface water that ecosystems mobilize for evapotranspiration (ET) remains unclear, because it represents only part of the total subsurface storage. To address this gap, we develop a catchment‐scale, ecosystem‐oriented hybrid machine learning model that integrates a parsimonious ecohydrological structure with data‐driven flexibility to infer time‐varying active root zone storage (a S rz ) as a latent state variable. Without prescribing rooting depth or soil layers, the model learns adaptive water partitioning from multi‐source observations of ET, runoff, snow, and terrestrial water storage, enabling diagnosis of both dynamic a S rz and its realized capacity. Applied across hundreds of U.S. catchments over the period 2001–2020, the framework reveals coherent spatial and hydroclimatic patterns, with a S rz peaking in transitional regions where atmospheric demand and water supply are balanced. The realized capacity reflects how belowground water access varies with long‐term hydroclimatic and substrate constraints. We further show that defining storage as a realized quantity through system dynamics improves stability and interpretability under varying observational and structural conditions. Overall, this study demonstrates how hybrid modeling can be used to diagnose ecosystem‐accessible water storage as a latent state, providing a physically consistent and observation‐informed pathway to quantify belowground processes that remain inaccessible to direct measurement and control key land‐atmosphere interactions.
SN - 0043-1397
SN - 1944-7973
ER -