Lopez et al. (2025) Evaluating a Simple Algorithm for an Evapotranspiration Retrieval Energy Balance Model in Mediterranean Citrus Orchards

Identification

• Journal: Water
• Year: 2025
• Date: 2025-11-18
• Authors: Kevin Alain Salamanca Lopez, Gila Abílio João, Hewlley Maria Acioli Imbuzeiro, Daniela Vanella, Simona Consoli, Giuseppe Longo-Minnolo, Gabrielle Ferreira Pires, José Francisco de Oliveira‐Júnior
• DOI: 10.3390/w17223286

Research Groups

• Agricultural Engineering Department, Universidade Federal de Viçosa (UFV), Brazil.
• Dipartimento di Agricoltura, Alimentazione e Ambiente (Di3A), Università degli Studi di Catania, Italy.
• Institute of Atmospheric Sciences (ICAT), Federal University of Alagoas (UFAL), Brazil.

Short Summary

This study evaluates the SAFER (Simple Algorithm for Evapotranspiration Retrieving) model's ability to estimate actual evapotranspiration in a Mediterranean citrus orchard using Sentinel-2 imagery and Eddy Covariance data. The findings indicate that while the model is highly accurate during wet seasons, its performance declines during dry periods due to its limited sensitivity to plant physiological water stress.

Objective

• To evaluate and calibrate the SAFER model for estimating actual crop evapotranspiration ($ET_a$) and surface energy balance (SEB) components in a Mediterranean citrus orchard to support irrigation management.

Study Configuration

• Spatial Scale: A 0.7-hectare orange orchard (Citrus sinensis cv. "Tarocco Sciara") located in Lentini, Sicily, Italy.
• Temporal Scale: Two years of observation (2021–2022), covering distinct wet and dry seasons.

Methodology and Data

• Models used: SAFER (Simple Algorithm for Evapotranspiration Retrieving) for spatializing energy fluxes and the FAO-56 Penman-Monteith model for reference evapotranspiration ($ET_0$).
• Data sources:
  • Satellite: Sentinel-2 MSI imagery (10 m spatial resolution) processed via Google Earth Engine.
  • Observation: Eddy Covariance (EC) flux tower equipped with a 3D sonic anemometer (CSAT3) and an infrared gas analyzer (Li-7500); soil heat flux plates and net radiometers.
  • Reanalysis/Meteorological: Data from the Sicilian Agrometeorological Information Service (SIAS).
• Calibration: Linear regression between the natural logarithm of the observed evaporative fraction and the remote sensing-derived variable $(LST \cdot a_0^{-1} \cdot NDVI^{-1})$.

Main Results

• Model Accuracy: The model showed high reliability during the wet season ($R^2$ of 0.85 to 0.89; $RMSE$ of 0.91 to 0.95 mm day⁻¹).
• Dry Season Performance: Accuracy decreased significantly ($R^2$ of 0.17 to 0.35; $RMSE$ of 0.68 to 0.86 mm day⁻¹) due to the model's inability to detect stomatal regulation and physiological stress through vegetation indices alone.
• Energy Partitioning: During summer, sensible heat ($H$) dominated over latent heat ($LE$), with Bowen ratios ($\beta$) exceeding 1.2, indicating severe water stress.
• Spatial Variability: SAFER successfully mapped $ET_a$ heterogeneity across the orchard, with daily standard deviations ranging from 0.2 to 0.8 mm day⁻¹, identifying zones for potential precision irrigation.
• Calibration Coefficients: Local calibration for Sicily yielded an intercept ($a$) of -0.463 and a slope ($b$) of -0.002.

Contributions

• Provides the first specific evaluation of the SAFER model for Mediterranean citrus orchards, demonstrating its utility as a cost-effective tool for regional water management.
• Highlights the limitations of NDVI-based energy balance models in water-limited environments and suggests the integration of additional stress-adjustment factors or machine learning to improve dry-season estimates.
• Validates the use of high-resolution Sentinel-2 data for irrigation zoning in small-scale Mediterranean agro-ecosystems.

Funding

• Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).
• Coordination for the Improvement of Higher Education Personnel (CAPES), award number 001.
• PRIN 2022 project "SWAM4Crops" (Smart Technologies and Remote Sensing methods to support the Sustainable Agriculture Water Management of Mediterranean Woody Crops).

Citation

@article{Lopez2025Evaluating,
  author = {Lopez, Kevin Alain Salamanca and João, Gila Abílio and Imbuzeiro, Hewlley Maria Acioli and Vanella, Daniela and Consoli, Simona and Longo-Minnolo, Giuseppe and Pires, Gabrielle Ferreira and Oliveira‐Júnior, José Francisco de},
  title = {Evaluating a Simple Algorithm for an Evapotranspiration Retrieval Energy Balance Model in Mediterranean Citrus Orchards},
  journal = {Water},
  year = {2025},
  doi = {10.3390/w17223286},
  url = {https://doi.org/10.3390/w17223286}
}

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