Tiengou et al. (2026) Regional impacts of irrigation on the atmospheric and terrestrial water cycle of the Iberian Peninsula in a climate model

Identification

• Journal: Earth System Dynamics
• Year: 2026
• Date: 2026-06-26
• Authors: Pierre Tiengou, Agnès Ducharne, Frédérique Cheruy
• DOI: 10.5194/esd-17-843-2026

Research Groups

• METIS, IPSL, Sorbonne Université/CNRS/EPHE-PSL, Paris, France
• Laboratoire de Météorologie Dynamique, IPSL, Sorbonne Université/CNRS/École Normale Supérieure–PSL Research/Ecole Polytechnique-IPP, Paris, France

Short Summary

This study uses a regional climate model to simulate the impacts of irrigation on the atmospheric and terrestrial water cycle of the Iberian Peninsula. It finds that irrigation improves model agreement with observations for river discharge and evapotranspiration, leading to local cooling, atmospheric moistening, and non-local precipitation increases over surrounding mountainous areas.

Objective

• To investigate the regional impacts of irrigation on land-atmosphere coupling variables and the atmospheric and terrestrial water cycle of the Iberian Peninsula using a regional climate model.

Study Configuration

• Spatial Scale: Iberian Peninsula, simulated on a hexagonal grid with 25 km resolution, interpolated to a longitude-latitude grid of similar resolution. The domain is a hexagon centered at 40.4° N, -3.7° E with a radius of 1500 km.
• Temporal Scale: 13 years (2010–2022), preceded by a 3-year spin-up (2007–2009).

Methodology and Data

• Models used:
  • Atmospheric component: ICOLMDZ (DYNAMICO dynamical core, LMDZ6A physics version NPv6.2).
  • Land surface model: ORCHIDEE v2.2.
  • Coupled IPSL climate model in a Limited Area Model (LAM) configuration.
  • River routing and irrigation scheme: Water-conservative supply-and-demand approach (based on Arboleda-Obando et al., 2024).
• Data sources:
  • Lateral boundary conditions: ERA5 reanalysis (hourly, 0.25° resolution).
  • Soil texture map: USDA (Reynolds et al., 2000).
  • Vegetation (Plant Functional Types): Land Use Harmonization 2 (LUHv2) dataset (Hurtt et al., 2020).
  • Digital Elevation Model (DEM): MERIT DEM (Yamazaki et al., 2019).
  • Irrigated fraction: Historical Irrigation Dataset (HID, Siebert and Döll, 2010).
  • Irrigation equipment type: Siebert et al. (2010) map.
  • Precipitation evaluation: Global Precipitation Climatology Centre (GPCC) Full Data Monthly Product Version 2020 (Rustemeier et al., 2020).
  • Evapotranspiration (ET) evaluation: Global Land Evaporation Amsterdam Model (GLEAM) v4 (Miralles et al., 2025).
  • Surface Soil Moisture (SSM) evaluation: European Space Agency Climate Change Initiative (ESA CCI) COMBINED product (Dorigo et al., 2017; Gruber et al., 2019).
  • Irrigation evaluation (Ebro Valley): ESA Irrigation+ project (Dari et al., 2023).
  • River discharge evaluation: Global Runoff Data Center (GRDC, Fekete, 2003).

Main Results

• Simulated irrigation is often constrained by water availability, being more realistic in northern regions (e.g., Ebro Valley) where surface water withdrawals are dominant, but underestimated in southern regions due to a lack of available water and absence of river dam representation.
• In the Ebro Basin, simulated irrigation (0.20 mm/d) shows good agreement with remote sensing estimates (0.23 mm/d) during summer, despite spatial biases.
• Irrigation significantly improves river discharge simulation, reducing the mean bias by 41.8% and the root mean square error (RMSE) by 7.12% on average, particularly in summer and autumn.
• While precipitation is underestimated in summer and overestimated in mountainous regions, irrigation partially alleviates the evapotranspiration (ET) dry bias. Surface soil moisture (SSM) is not strongly impacted, as most additional water is evaporated.
• During summer (June-August), irrigation leads to:
  • An increase in latent heat flux and a decrease in sensible heat flux, up to 50 W/m².
  • A lowering of 2 m air temperature by up to 0.35 K.
  • A reduction in atmospheric boundary layer height by up to 100 m.
  • A lowering of the lifting condensation level (LCL) by up to 250 m.
  • Statistically significant increases in precipitation over mountainous areas surrounding the Ebro Valley, linked to increases in convective available potential energy (CAPE).
• Continental moisture recycling is observed, where increases in ET (112% of irrigation volume) exceed the amount of water added by irrigation, enabled by systematic increases in precipitation (25% of irrigation volume) over the domain. This recycling is mostly nonlocal, with additional rainfall occurring more in lightly irrigated regions than in intensely irrigated ones.

Contributions

• Presents the first regional climate simulations over the Iberian Peninsula using the land surface (ORCHIDEE) and atmospheric (ICOLMDZ) components of the global IPSL climate model in a new limited area model configuration (25 km resolution).
• Provides a multiyear (decadal) analysis of regional irrigation impacts on land-atmosphere coupling and the water cycle using a water-conservative irrigation parametrization, contrasting with shorter-term mesoscale studies.
• Demonstrates that explicit irrigation representation significantly improves the model's fidelity in simulating river discharge and evapotranspiration in the Iberian Peninsula.
• Identifies and quantifies nonlocal atmospheric moisture recycling, where irrigation in intensely irrigated areas leads to increased precipitation in surrounding lightly irrigated mountainous regions.
• Lays the groundwork for future comparisons of the IPSL model with high-resolution field observations from campaigns like LIAISE.

Funding

• French National Research Agency (ANR) under grant no. ANR-21-SOIL-0001.
• Agence Nationale de la Recherche – France 2030 as part of the PEPR TRACCS programme under grant number ANR-22-EXTR-0008.

Citation

@article{Tiengou2026Regional,
  author = {Tiengou, Pierre and Ducharne, Agnès and Cheruy, Frédérique},
  title = {Regional impacts of irrigation on the atmospheric and terrestrial water cycle of the Iberian Peninsula in a climate model},
  journal = {Earth System Dynamics},
  year = {2026},
  doi = {10.5194/esd-17-843-2026},
  url = {https://doi.org/10.5194/esd-17-843-2026}
}