Moazenzadeh (2026) Application of time-lagged satellite image-based crop coefficients for estimating actual evapotranspiration through FAO-56 method

Identification

• Journal: Scientific Reports
• Year: 2026
• Date: 2026-02-01
• Authors: Roozbeh Moazenzadeh
• DOI: 10.1038/s41598-026-38365-2

Research Groups

• Department of Water Engineering, Faculty of Agriculture, Shahrood University of Technology, Shahrood, Iran

Short Summary

This study investigated the feasibility of using 10-year time-lagged satellite-derived crop coefficients (Kc) with the FAO-56 method to estimate actual evapotranspiration (AET) in the Neishaboor watershed, Iran, finding it a useful and computationally simpler approach for water management when current Kc data are unavailable.

Objective

• To evaluate the utility and accuracy of estimating actual evapotranspiration (AET) using the FAO-56 method with 10-year time-lagged crop coefficients (Kc) derived from satellite imagery, particularly when current Kc data are unavailable at the pixel scale.

Study Configuration

• Spatial Scale: Neishaboor watershed, Iran (approximately 9158 km²), focusing on 10 agricultural subbasins. Satellite imagery processed at various resolutions (250 m, 500 m, 1000 m).
• Temporal Scale: Crop coefficients (Kc) extracted from April to October 2009. Actual evapotranspiration (AET) estimated for the corresponding months in 2019. Meteorological data for 2009 and 2019.

Methodology and Data

• Models used:
  • FAO-56 method (for AET estimation using Kc and ETo)
  • SEBAL (Surface Energy Balance Algorithm for Land) algorithm (for benchmark AET and Kc derivation)
  • FAO-recommended Penman-Monteith equation (FAO 56-PM) (for reference evapotranspiration, ETo, calculation)
• Data sources:
  • MODIS satellite images (TERRA platform, cloud-free, April-October 2009 and 2019)
  • Meteorological data (temperature, wind speed, relative humidity, sunshine hours) from Neishaboor synoptic station

Main Results

• The average AET estimation error (RMSE) across the 10 studied subbasins ranged from 0.53 mm/day to 1.47 mm/day.
• Mean error rates for AET intervals [0–2), [2–4), [4–6), and ≥ 6 mm were 0.71 mm/day, 0.68 mm/day, 0.73 mm/day, and 0.64 mm/day, respectively.
• The method's performance was classified as "good" in August, "almost good" in June, "fair" in July, September, and October, and "poor" in April and May, based on the Ertekin and Yaldiz (2000) classification.
• Approximately 58% (April), 37% (May), 68% (June), 43% (July), 73% (August), 50% (September), and 86% (October) of residual AET values fell within ± 0.5 mm/day.
• The proposed method generally avoided egregious, systematic underestimation or overestimation of AET.

Contributions

• Demonstrates a practical and computationally simplified approach for estimating AET at the watershed level by utilizing time-lagged (10-year) satellite-derived Kc values with the FAO-56 method.
• Provides a valuable tool for water resources management decisions in data-scarce regions, particularly when real-time Kc data are unavailable.
• Highlights the critical influence of land use changes, climatic variations, and water management practices on the accuracy of time-lagged AET estimations.

Funding

• This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Citation

@article{Moazenzadeh2026Application,
  author = {Moazenzadeh, Roozbeh},
  title = {Application of time-lagged satellite image-based crop coefficients for estimating actual evapotranspiration through FAO-56 method},
  journal = {Scientific Reports},
  year = {2026},
  doi = {10.1038/s41598-026-38365-2},
  url = {https://doi.org/10.1038/s41598-026-38365-2}
}