Kumambala et al. (2026) Estimating reference evapotranspiration in data-scarce regions: Comparative analysis and calibration of empirical models against the Penman-Monteith method in Malawi

Identification

• Journal: Physics and Chemistry of the Earth Parts A/B/C
• Year: 2026
• Date: 2026-01-09
• Authors: Patsani Gregory Kumambala, Lenard Kumwenda, Deogratias M.M. Mulungu, Sheila Kavwenje
• DOI: 10.1016/j.pce.2026.104269

Research Groups

• Lilongwe University of Agriculture and Natural Resources, Natural Resources College, Lilongwe, Malawi
• Lilongwe University of Agriculture and Natural Resources, Bunda College, Agricultural Engineering Department, Lilongwe, Malawi
• University of Dar es Salaam, College of Engineering and Technology, Department of Water Resources Engineering, Dar es Salaam, Tanzania

Short Summary

This study evaluated and calibrated three empirical reference evapotranspiration (ET0) models (Hargreaves–Samani, Priestley–Taylor, and Turc) against the FAO-56 Penman–Monteith standard in data-scarce regions of Malawi. The calibrated radiation-based models (Turc and Priestley–Taylor) were found to be robust, low-data alternatives, particularly in humid and moderate-wind environments.

Objective

• To evaluate and calibrate empirical reference evapotranspiration (ET0) models (Hargreaves–Samani, Priestley–Taylor, and Turc) against the FAO-56 Penman–Monteith method in data-scarce regions of Malawi to identify robust, low-data alternatives for irrigation planning and hydrological modeling.

Study Configuration

• Spatial Scale: Six meteorological stations representing major agro-climatic zones across Malawi.
• Temporal Scale: Daily meteorological data aggregated to monthly scales.

Methodology and Data

• Models used:
  • Empirical models: Hargreaves–Samani (HS), Priestley–Taylor (PT), Turc.
  • Reference model: FAO-56 Penman–Monteith (PM).
  • Calibration method: Linear regression.
  • Statistical tests: F-test, Jarque–Bera test.
• Data sources:
  • Department of Climate Change and Meteorological Services in Malawi.
  • Variables: Daily temperature, humidity, wind speed, and sunshine duration.

Main Results

• Radiation-based models (Priestley–Taylor and Turc) consistently outperformed the temperature-based Hargreaves–Samani method.
• The calibrated Turc model achieved the highest accuracy with R² values ranging from 0.79 to 0.94.
• The calibrated Priestley–Taylor model showed good accuracy with R² values from 0.55 to 0.95.
• The Hargreaves–Samani method exhibited lower accuracy (R² = 0.40–0.74) and strong sensitivity to wind speed.
• Model performance generally declined from humid highland regions to arid lakeshore regions, indicating the significant influence of aerodynamic factors.
• Overall, the calibrated Turc and Priestley–Taylor models provide robust, low-data alternatives to the FAO-56 Penman–Monteith method, especially suitable for humid and moderate-wind environments.

Contributions

• Provides a comparative analysis and calibration of empirical ET0 models specifically tailored for data-scarce tropical regions like Malawi.
• Identifies and validates robust, low-data alternative ET0 estimation methods (calibrated Turc and Priestley–Taylor) for practical application where full meteorological data for Penman–Monteith is unavailable.
• Offers practical tools to support irrigation management, drought monitoring, and water-resource assessment in similar data-limited settings.

Funding

• Not specified in the provided text.

Citation

@article{Kumambala2026Estimating,
  author = {Kumambala, Patsani Gregory and Kumwenda, Lenard and Mulungu, Deogratias M.M. and Kavwenje, Sheila},
  title = {Estimating reference evapotranspiration in data-scarce regions: Comparative analysis and calibration of empirical models against the Penman-Monteith method in Malawi},
  journal = {Physics and Chemistry of the Earth Parts A/B/C},
  year = {2026},
  doi = {10.1016/j.pce.2026.104269},
  url = {https://doi.org/10.1016/j.pce.2026.104269}
}