Alzabari (2026) Spatiotemporal variability and climatic determinants of reference evapotranspiration in Saudi Arabia

Identification

• Journal: Water Science & Technology Water Supply
• Year: 2026
• Date: 2026-01-01
• Authors: Fawaz Alzabari
• DOI: 10.2166/ws.2026.109

Research Groups

• Civil Engineering Department, College of Engineering, Najran University, Najran, Saudi Arabia

Short Summary

This study investigated the spatiotemporal variability, long-term trends, and climatic sensitivity of reference evapotranspiration (ET0) across 25 meteorological stations in Saudi Arabia from 2000 to 2024, revealing statistically significant increasing ET0 trends, particularly in summer, primarily driven by mean relative humidity, wind speed, and maximum air temperature.

Objective

• To investigate the temporal variability, long-term trends, and climatic sensitivity of reference evapotranspiration (ET0) across Saudi Arabia to enhance irrigation scheduling, reduce over-irrigation, and support sustainable water use in agriculture.

Study Configuration

• Spatial Scale: 25 meteorological stations distributed throughout Saudi Arabia, covering diverse climatic zones.
• Temporal Scale: Daily data from 2000 to 2024 (25 years).

Methodology and Data

• Models used:
  • FAO-56 Penman–Monteith method for ET0 estimation.
  • Mann–Kendall test for trend detection.
  • Sen’s slope estimator for quantifying trend magnitude.
  • Standardised Multiple Linear Regression (MLR) for sensitivity analysis of climatic drivers.
• Data sources:
  • Daily meteorological data for 25 stations from the National Center of Meteorology (NCM) of Saudi Arabia.
  • Variables included: maximum, minimum, and mean air temperature (°C), mean relative humidity (%), and mean wind speed (m/s).
  • Solar radiation was estimated using standard FAO-56 methods due to lack of direct measurements.

Main Results

• The majority of stations (23 out of 25) experienced statistically significant increasing trends in ET0.
• Increasing ET0 trends were most widespread and pronounced during the summer months (May to September), coinciding with peak solar radiation and low humidity.
• Stations such as Wadi Al-Dawasser, Sharorah, and Najran exhibited the strongest upward trends, with Sen’s slope values exceeding 4 mm per month during summer (e.g., Sharorah: 5.10 mm/month/year in June; Najran: 4.11 mm/month/year in July).
• A few stations, notably Dammam, Gassim, and Riyadh, showed decreasing trends in specific months, potentially linked to local coastal microclimatic changes or urbanisation effects.
• Sensitivity analysis revealed that mean relative humidity was the most influential climatic driver of ET0, contributing 27.2% to its variability.
• Wind speed was the second most important driver, contributing 24.7%, followed closely by maximum air temperature at 24.6%. Mean temperature contributed 14.1%, and minimum temperature 9.4%.

Contributions

• Provides a comprehensive, long-term (2000–2024) assessment of ET0 trends across 25 meteorological stations covering major climatic zones of Saudi Arabia, addressing gaps in previous studies limited by short records or narrow spatial coverage.
• Integrates robust non-parametric trend detection (Mann–Kendall and Sen’s slope) with regression-based diagnostics to quantify the relative contribution of key climatic variables to ET0 variability.
• Offers evidence-based insights crucial for guiding irrigation planning, improving agricultural efficiency, and developing climate-resilient water management strategies in line with Saudi Vision 2030.
• Highlights the critical role of relative humidity and wind speed, alongside temperature, in driving ET0 variability in arid environments.

Funding

Not explicitly mentioned in the paper.

Citation

@article{Alzabari2026Spatiotemporal,
  author = {Alzabari, Fawaz},
  title = {Spatiotemporal variability and climatic determinants of reference evapotranspiration in Saudi Arabia},
  journal = {Water Science & Technology Water Supply},
  year = {2026},
  doi = {10.2166/ws.2026.109},
  url = {https://doi.org/10.2166/ws.2026.109}
}