Moucha et al. (2025) Projection of irrigation water requirement in the south Mediterranean area using an explicit representation of irrigation processes into a land surface model: Case of the Tensift catchment (Morocco)

Identification

• Journal: PLOS Water
• Year: 2025
• Authors: Ahmed Moucha, Lionel Jarlan, Pere Quintana Seguí, Anaïs Barella-Ortiz, Michel Le Page, Simon Munier, Adnane Chakir, Aaron Boone, Fathallah Sghrer, Jean-Christophe Calvet, Lahoucine Hanich
• DOI: 10.1371/journal.pwat.0000297

Research Groups

• L3G Laboratory, Faculty of Sciences and Techniques, Cadi Ayyad University, Marrakech, Morocco
• Direction Générale de la Météorologie, Casablanca, Morocco
• CESBIO (Université de Toulouse/CNRS/INRAE/IRD/CNES), Toulouse, France
• Observatori de l’Ebre, Ramon Llull University - CSIC, Tarragona, Spain
• CNRM (Université de Toulouse/Météo-France/CNRS), Toulouse, France
• LMFE, Faculty of Sciences Semlalia, Cadi Ayyad University, Marrakech, Morocco
• ORMVAH-Office Régional de Mise en Valeur Agricole du Haouz, Marrakech, Morocco
• Geology and Sustainable Mining Institute (GSMI), Mohammed VI Polytechnic University (UM6P), Ben Guerir, Morocco

Short Summary

This study evaluates a new irrigation module in the ISBA land surface model using data from the semi-arid Tensift catchment (Morocco) and projects future agricultural water requirements, finding that water use could nearly double by 2050, primarily driven by land use change (conversion to water-intensive tree crops) rather than climate change alone.

Objective

• To evaluate the performance of the new explicit irrigation module integrated into the Interactions between Soil, Biosphere, and Atmosphere (ISBA) land surface model.
• To assess the future trajectories of agricultural water use in the south Mediterranean area, considering combined impacts of climate change and land use change (conversion to tree crops).

Study Configuration

• Spatial Scale: Tensift catchment (watershed) in Morocco (19,800 km²), with model grid point dimensions ranging from 1 km² to 8 km².
• Temporal Scale: Historical period (2004–2014) for model evaluation; Future projection horizon (2041–2060, referred to as 2050).

Methodology and Data

• Models used:
  • ISBA (Interactions between Soil, Biosphere, and Atmosphere) Land Surface Model, specifically the ISBA-A-gs scheme with a new explicit irrigation module (Druel et al., 2022).
  • SURFEX platform (used to embed ISBA).
  • SAFRAN re-analysis system (for historical meteorological forcing).
  • EURO-CORDEX ensemble (for future climate projections, downscaled using quantile-quantile and delta change methods).
• Data sources:
  • Eddy-Covariance stations (Agafay, Agdal, R3, Saada, Bour) measuring Latent Heat Flux (LE) and Sensible Heat Flux (H).
  • Monthly irrigation water amounts provided by ORMVAH (Regional Office for Agricultural Development of Haouz) at the irrigated perimeter scale (2004–2014).
  • ECOCLIMAP Second Generation (land cover map, modified to reflect local changes).
  • MODIS NDVI (used to compute annual land use maps and tree cover fraction trends).
  • Copernicus Global Land Service (albedo and Leaf Area Index climatology at 300 m resolution).
  • Global Soil grids (soil texture data).
  • Meier et al. (2018) global irrigation map (used as a base for potentially irrigated areas).
  • Climate Scenarios: RCP4.5 and RCP8.5.
  • Land Use Scenarios: Historical, Baseline (linear trend extrapolation of tree conversion), and Inflexion (limited conversion).

Main Results

• Model Performance: The integration of the new irrigation scheme significantly improved the prediction of Latent Heat Flux (LE). The average LE flux bias across all flux stations was reduced from approximately -60 W/m² (without irrigation) to -15 W/m² (with irrigation).
• Irrigation Water Amounts: The model successfully reproduced the overall magnitude and seasonality of observed irrigation water quantities at the perimeter scale, although it exhibited a positive bias, likely due to the model assuming optimal irrigation (a "perfect farmer") versus real-world water scarcity and management constraints.
• Water Budget (Historical): On average over the irrigated areas, annual water supply was 563 mm/year for wheat and 1,454 mm/year for tree crops (equivalent to 5,630 m³/ha and 14,540 m³/ha, respectively). Drainage (groundwater recharge) was an order of magnitude lower than other fluxes, and most recharge occurred at the foothills of the Atlas Mountains, not in the irrigated plains.
• Future Projections (2050 Horizon):
  • Climate Change Impact: Precipitation is expected to decrease by 6% (RCP4.5) to 21% (RCP8.5) across the catchment. Climate change alone increases irrigation water supply by only 10% to 16%.
  • Land Use Change Impact: The conversion to water-intensive tree crops (Baseline scenario) combined with RCP8.5 leads to the most extreme scenario, where total irrigation water supply could almost double (from 790 million cubic meters (Mm³) to over 1,500 Mm³ annually).
  • Dominant Driver: The drastic increase in future agricultural water demand is primarily attributed to land use change (intensification and expansion of irrigated tree crops) rather than climate change effects (warming and precipitation decrease).

Contributions

• First direct evaluation of the ISBA model's new irrigation scheme using in-situ irrigation water amount observations in a semi-arid Mediterranean catchment (Tensift, Morocco).
• Quantifies the relative impacts of climate change versus land use change (conversion to drip-irrigated tree crops) on future agricultural water requirements in the South Mediterranean.
• Highlights the "rebound effect" of public policies promoting drip irrigation, showing that the conversion to water-intensive crops and expansion of irrigated areas significantly outweighs the water-saving potential of the technology, leading to unsustainable pressure on water resources.
• Provides a comprehensive water budget analysis for the Tensift catchment, confirming that deep drainage and groundwater recharge are low in the irrigated plains.

Funding

• FP7 ERANET-MED CHAAMS project
• H2020 PRIMA IDEWA project
• RISE-H2020 ACCWA project

Citation

@article{Moucha2025Projection,
  author = {Moucha, Ahmed and Jarlan, Lionel and Quintana‐Seguí, Pere and Barella-Ortiz, Anaïs and Page, Michel Le and Munier, Simon and Chakir, Adnane and Boone, Aaron and Sghrer, Fathallah and Calvet, Jean-Christophe and Hanich, Lahoucine},
  title = {Projection of irrigation water requirement in the south Mediterranean area using an explicit representation of irrigation processes into a land surface model: Case of the Tensift catchment (Morocco)},
  journal = {PLOS Water},
  year = {2025},
  doi = {10.1371/journal.pwat.0000297},
  url = {https://doi.org/10.1371/journal.pwat.0000297}
}

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