Witt et al. (2026) Evaluating Simulated Groundwater Contributions to Streamflow in a Data‐Scarce, Semi‐Arid Catchment in South Africa

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Hydrological Processes
• Year: 2026
• Date: 2026-01-01
• Authors: Marlene de Witt, Francois Roets, Andrew Watson
• DOI: 10.1002/hyp.70385

Research Groups

Not explicitly mentioned in the abstract.

Short Summary

This study assesses four calibration procedures for simulating groundwater contribution to streamflow in the data-deficient Goukou catchment, South Africa, using the J2000 hydrological model and stable isotopes for complementary evaluation. It found that the DREAM calibration procedure provided the best balance between realistic groundwater flow proportion and model efficiency, while isotopes proved effective in validating model results and highlighting shortcomings due to data scarcity.

Objective

• To assess four calibration procedures (NSGA2, DREAM, MCA, LHC) for simulating groundwater contribution to streamflow in the semi-arid, data-deficient Goukou catchment of South Africa, and to test the model realism through a complementary evaluation with stable isotopes.

Study Configuration

• Spatial Scale: Goukou catchment, South Africa.
• Temporal Scale: Not explicitly mentioned in the abstract, but implied to cover a period sufficient for hydrological processes and isotopic characterization.

Methodology and Data

• Models used: J2000 (fully distributed, conceptual rainfall-runoff model). Calibration procedures: Non-dominated Sorting Genetic Algorithms-2 (NSGA2), DiffeRential Evolution Adaptive Metropolis (DREAM), Monte Carlo Analysis (MCA), Latin Hypercube (LHC).
• Data sources: Stable isotopes (for complementary evaluation), hydroclimatic data (noted as sparse/lacking).

Main Results

• DREAM performed best, finding a parameter set with a good balance between a realistic groundwater flow proportion (~31% for the Table Mountain Group aquifer) and fair Nash Sutcliffe efficiencies (~0.38) for streamflow.
• Isotopic characterisation showed that the catchment is recharged episodically during the most intense rainfall events, with precipitation to groundwater ratios all having negative values.
• Isotopes corroborated modelled groundwater contribution to streamflow in the upper part of the catchment but suggested overestimation by J2000 in the middle section.

Contributions

• Demonstrated the effectiveness of stable isotopes in validating hydrological model results and detecting shortcomings, particularly in data-scarce regions and complex climatic transition zones.
• Provided evidence that the selection of calibration procedures should be carefully considered in data-scarce circumstances, as good model efficiency does not necessarily guarantee a realistic representation of hydrological processes.

Funding

Not mentioned in the abstract.

Citation

@article{Witt2026Evaluating,
  author = {Witt, Marlene de and Birkel, Christian and Roets, Francois and Watson, Andrew},
  title = {Evaluating Simulated Groundwater Contributions to Streamflow in a Data‐Scarce, Semi‐Arid Catchment in South Africa},
  journal = {Hydrological Processes},
  year = {2026},
  doi = {10.1002/hyp.70385},
  url = {https://doi.org/10.1002/hyp.70385}
}