Claro et al. (2026) Olive area expansion under climate change: a CMIP6-SWAT+ basin-scale water balance and demand assessment in southern Portugal

Identification

• Journal: Agricultural Water Management
• Year: 2026
• Date: 2026-10-21
• Authors: André M. Claro, André Fonseca, Carina Almeida, Hélder Fraga, João A. Santos
• DOI: 10.1016/j.agwat.2026.110874

Research Groups

• Centre for the Research and Technology of Agro-Environmental and Biological Sciences (CITAB), Universidade de Tr´as-os-Montes e Alto Douro (UTAD), Vila Real, Portugal
• Institute for Innovation, Capacity Building and Sustainability of Agri-Food Production (Inov4Agro), Vila Real, Portugal
• BIORG—Bioengineering and Sustainability Research Group, Faculty of Engineering, Lus´ofona University, Lisbon, Portugal
• LEAF—Linking Landscape, Environment, Agriculture and Food, Instituto Superior de Agronomia, Universidade de Lisboa, Lisbon, Portugal

Short Summary

This study quantifies the impact of projected climate aridification (SSP5-8.5 scenario) and olive grove expansion on the Sado River Basin's water balance and olive water demand in southern Portugal using the SWAT+ model. It reveals that climate change alone could increase olive irrigation demand by 17%, while combined with a 106% olive area expansion, total irrigation demand could surge by 141%, significantly stressing local water resources.

Objective

• Configure, calibrate, and validate a SWAT+ agro-hydrological model for the Sado River Basin (SRB).
• Characterize projected mid-century climate change (2041–2070) over the SRB under the SSP5–8.5 scenario using high-resolution CMIP6-derived climate projections.
• Quantify the future water demand of SRB olive groves under two scenarios: solely climate change, and combined climate change with olive grove area expansion.

Study Configuration

• Spatial Scale: Sado River Basin (SRB), Portugal, covering 6529 km². Atmospheric data at 10 km resolution, topography at 25 m resolution, and stream networks at 1:25000 scale.
• Temporal Scale:
  • Calibration: 1962–1971 (monthly flow rates)
  • Validation: 1981–1990 (monthly flow rates)
  • Historical simulations: 1981–2010 (30-year period)
  • Future simulations: 2041–2070 (30-year period)

Methodology and Data

• Models used:
  • SWAT+ (Soil & Water Assessment Tool – Plus) agro-hydrological model (revision 61.0.1)
  • CMIP6 (Coupled Model Intercomparison Project Phase 6) General Circulation Models (GCMs) ensemble: GFDL-ESM4, IPSL-CM6A-LR, MPI-ESM1–2-HR.
• Data sources:
  • Topography: European Digital Elevation Model (EU-DEM) version 1.1.
  • Channels/Streams: Portuguese Environmental Information System (SNIAmb).
  • Land Use/Land Cover (LULC): Portuguese General Directorate of Territory (DGT) 2018 soil occupation chart (COS2018).
  • Soil Data: Harmonized World Soil Database v2.0 (HWSD), SNIAmb (hydrological soil group), European Soil Database (ESDB) (rooting depth), HiHydroSoilV2.0 (saturated hydraulic conductivity).
  • Weather Data (Calibration/Validation): ERA5-Iberia (10 km spatial resolution, bias-adjusted ERA5-Land reanalysis for precipitation, maximum/minimum temperature), European Climate Assessment & Dataset (ECA&D) (monthly climatological dataset for solar radiation, dew-point temperature, wind intensity).
  • Weather Data (Simulations): NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) from CMIP6 GCMs (downscaled to 1 km, then remapped to 10 km) for precipitation, maximum/minimum temperature under SSP5–8.5 scenario.

Main Results

• Climate Projections (2041-2070 under SSP5-8.5): Annual precipitation is projected to decrease by approximately 100 mm (16–18%), while maximum and minimum temperatures are expected to increase by 2.1–2.6 °C and 1.7–2.0 °C, respectively. Potential evapotranspiration (PET) is projected to increase by approximately 9%.
• Water Balance Impacts: Surface runoff, lateral flow, return flow, and percolation to shallow and deep aquifers are projected to decrease significantly (29–47%). Evapotranspiration (ET) could account for approximately 90% of annual precipitation, up from 80% historically.
• Olive Water Demand:
  • Under climate change alone (F1 scenario), mean annual total-volume olive irrigation is projected to increase by 17% (from 90 hm³ to approximately 106 hm³).
  • Under combined climate change and a 106% olive grove area expansion (F2 scenario), mean annual total-volume olive irrigation is projected to increase by 141% (from 90 hm³ to approximately 218 hm³).
  • The mean annual olive irrigation volume per unit area is projected to increase to 2528 m³/ha in both future scenarios.
  • The inter-annual variability range of olive irrigation is expected to increase by 24% (F1) and 34% (F2) relative to the historical range of 1400 m³/ha.

Contributions

• First study to integrate the SWAT+ agro-hydrological model with CMIP6 10 km resolution climate projections to simulate basin hydrology and olive water demand in the Sado River Basin, Portugal.
• Innovatively linked basin-scale olive irrigation demand with changes in surface runoff, evapotranspiration, subsurface flows, and groundwater recharge, providing a holistic view beyond parcel-scale assessments.
• Developed simple aridification and irrigation efficiency indicators (runoff–precipitation ratios, ET–precipitation ratios, olive irrigation needs per unit area) for local farmers and major stakeholders.
• Presents a methodology applicable to other Mediterranean or semi-arid regions facing perennial crop expansion and declining surface water resources under climate change.

Funding

• National Funds by FCT – Portuguese Foundation for Science and Technology:
  • UID/04033/2025: Centre for the Research and Technology of Agro-Environmental and Biological Sciences (https://doi.org/10.54499/UID/04033/2025)
  • LA/P/0126/2020 (https://doi.org/10.54499/LA/P/0126/2020)
• European Union - NextGenerationEU:
  • UID/PRR/04033/2025 (https://doi.org/10.54499/UID/PRR/04033/2025)
  • UID/PRR2/04033/2025 (https://doi.org/10.54499/UID/PRR2/04033/2025)
• MIT Portugal Partnership 2030 (MPP2030-FCT), grant number PRT/BD/154652/2023 (https://doi.org/10.54499/PRT/BD/154652/2023)

Citation

@article{Claro2026Olive,
  author = {Claro, André M. and Fonseca, André and Almeida, Carina and Fraga, Hélder and Santos, João A.},
  title = {Olive area expansion under climate change: a CMIP6-SWAT+ basin-scale water balance and demand assessment in southern Portugal},
  journal = {Agricultural Water Management},
  year = {2026},
  doi = {10.1016/j.agwat.2026.110874},
  url = {https://doi.org/10.1016/j.agwat.2026.110874}
}