Sheshadrivasan et al. (2026) GWSWEX v1.0: a dual-solver 1D unsaturated zone model for mass-conservative groundwater recharge and runoff computation in distributed hydrological modelling

Identification

• Journal: Geoscientific model development
• Year: 2026
• Date: 2026-09-07
• Authors: Veethahavya Kootanoor Sheshadrivasan, Jakub Langhammer
• DOI: 10.5194/gmd-19-8233-2026

Research Groups

• Department of Physical Geography and Geoecology, Faculty of Science, Charles University, Prague, Czech Republic

Short Summary

This paper introduces GWSWEX (Groundwater–Surface Water EXchange), a vertically resolved, process-based UZ coupler designed to address the gap between integrated 3-D models and bucket-style conceptual models. The model is tested against HYDRUS-1D as a representative iterative implicit Richards-equation reference for vertical 1-D variably saturated flow at the column scale.

Objective

• To develop a vertically resolved, process-based UZ coupler that can track a freely moving groundwater head within a layered, heterogeneous column and expose it as a prognostic state to an external GW model.
• To couple GW, UZ, and SW within a single mass-conservative framework using physically interpretable constitutive relations.

Study Configuration

• Spatial Scale: Column scale (1-D)
• Temporal Scale: Daily-interval experiment with 65 d horizon and hourly-interval experiment with 32 d horizon

Methodology and Data

• Models used: GWSWEX, HYDRUS-1D
• Data sources: Synthetic forcing with perfectly known parameters and boundary conditions

Main Results

• The explicit and implicit GWSWEX solvers show good agreement with HYDRUS-1D in terms of groundwater-head accuracy.
• Eleven out of twelve simulations attain a GWH RMSE ≤2 cm and NSE ≥0.85 under daily-interval forcing.
• The intensive-scenario residuals are larger, concentrated in the simulations dominated by a low-Ksat clay layer.

Contributions

• This study addresses the gap between integrated 3-D models and bucket-style conceptual models by introducing a vertically resolved, process-based UZ coupler.
• GWSWEX is designed to be computationally frugal enough for multi-decadal simulations, ensemble-grade calibration, projection, and sensitivity analyses.

Funding

• Not specified in the provided text.

Citation

@article{Sheshadrivasan2026GWSWEX,
  author = {Sheshadrivasan, Veethahavya Kootanoor and Langhammer, Jakub},
  title = {GWSWEX v1.0: a dual-solver 1D unsaturated zone model for mass-conservative groundwater recharge and runoff computation in distributed hydrological modelling},
  journal = {Geoscientific model development},
  year = {2026},
  doi = {10.5194/gmd-19-8233-2026},
  url = {https://doi.org/10.5194/gmd-19-8233-2026}
}