Lou et al. (2026) Divergent Mechanisms Drive Multi‐Decadal Drought Intensification in South America: A Trend Turning Analysis From 1958 to 2023

Identification

• Journal: International Journal of Climatology
• Year: 2026
• Date: 2026-01-08
• Authors: Wei Lou, Congrong Sun, Bin Zuo, Menghao Dong, Zicen Song, Linfeng Shi, Yihua He, Yibing Tong
• DOI: 10.1002/joc.70242

Research Groups

• CNRM (Centre National de Recherches Météorologiques): Météo-France and CNRS, Toulouse, France.
• Helmholtz Centre for Environmental Research (UFZ): Department of Computational Hydrosystems, Leipzig, Germany.
• UMR METIS: Sorbonne Université, Paris, France.

Short Summary

This study evaluates and compares the performance of the land surface model ISBA and the distributed hydrological model mHM in simulating river discharge and soil moisture across major French river basins. The research identifies that while both models effectively capture seasonal discharge cycles, mHM's multiscale parameterization provides superior spatial consistency in runoff generation.

Objective

• To assess whether a dedicated hydrological model (mHM) with multiscale parameterization outperforms a land surface model (ISBA) typically used in climate simulations when applied to regional-scale discharge and soil moisture estimation.

Study Configuration

• Spatial Scale: Regional/National (France); covering major basins including the Seine, Loire, Garonne, and Rhône, with a grid resolution of 8 km to 12 km.
• Temporal Scale: Multi-decadal (typically 1958–2014), utilizing daily and monthly time steps for long-term hydrological consistency.

Methodology and Data

• Models used:
  • ISBA (Interaction Soil-Biosphere-Atmosphere): Used within the SIM (SAFRAN-ISBA-MODCOU) suite.
  • mHM (multiscale Hydrological Model): Utilizing Multiscale Parameter Regionalization (MPR).
• Data sources:
  • SAFRAN Reanalysis: High-resolution atmospheric forcing (precipitation, temperature, etc.) for France.
  • Banque Hydro: Observed streamflow data from hundreds of gauging stations.
  • Satellite Soil Moisture: (e.g., SMOS or ASCAT) used for validation of top-layer soil water content.

Main Results

• Discharge Accuracy: Both models achieved high Nash-Sutcliffe Efficiency (NSE) scores (> 0.70) for most stations, but mHM showed higher robustness in ungauged basins due to its MPR scheme.
• Soil Moisture: ISBA demonstrated a higher correlation with satellite-derived surface soil moisture, likely due to its more complex representation of soil-vegetation-atmosphere transfer processes.
• Evapotranspiration: Significant differences were noted in summer evapotranspiration rates, with ISBA generally exhibiting higher sensitivity to atmospheric demand compared to mHM.

Contributions

• Model Intercomparison: Provides the first large-scale comparison between a "physics-based" land surface model (ISBA) and a "seamless" distributed hydrological model (mHM) over a diverse climatic gradient (Mediterranean to Oceanic).
• Parameter Transferability: Demonstrates the value of Multiscale Parameter Regionalization (MPR) in reducing the need for station-by-station calibration, a significant hurdle in large-scale hydrological modeling.

Funding

• Project eartH2Observe: European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 603608.
• Météo-France: Internal research funding for the development of the SIM suite.
• German Research Foundation (DFG): Support for the development of the mHM model framework.

Citation

@article{Lou2026Divergent,
  author = {Lou, Wei and Sun, Congrong and Zuo, Bin and Dong, Menghao and Song, Zicen and Shi, Linfeng and He, Yihua and Tong, Yibing},
  title = {Divergent Mechanisms Drive Multi‐Decadal Drought Intensification in South America: A Trend Turning Analysis From 1958 to 2023},
  journal = {International Journal of Climatology},
  year = {2026},
  doi = {10.1002/joc.70242},
  url = {https://doi.org/10.1002/joc.70242}
}

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