Othman et al. (2026) A comparative analysis of long-term spatiotemporal variability in precipitation 85 year-long reanalysis and observation data from 150 stations over arid MENA-T region

Identification

• Journal: Theoretical and Applied Climatology
• Year: 2026
• Date: 2026-02-01
• Authors: Nariman Yahya Othman, Berna Ayat
• DOI: 10.1007/s00704-026-06067-4

Research Groups

• Department of Civil Engineering, Yildiz Technical University, Esenler, Istanbul, Türkiye

Short Summary

This study comprehensively analyzed long-term spatiotemporal precipitation variability and trends across the MENA-T region using 85 years of in-situ and ERA5 reanalysis data, revealing a distinct north-south hydroclimatic dipole with increasing aridity in the south and intensifying extremes in the north.

Objective

• To systematically assess the long-term spatiotemporal variability and trends of 13 precipitation indices across the Middle East and North Africa and Türkiye (MENA-T) region using both in-situ observational data and ERA5 reanalysis, thereby providing critical insights into evolving precipitation patterns for water resource management and climate adaptation.

Study Configuration

• Spatial Scale: The Middle East and North Africa and Türkiye (MENA-T) region, spanning 12°N – 43°N latitude and −18°W – 63°E longitude, covering 16,546,112 square kilometers. This includes Algeria, Bahrain, Egypt, Iran, Iraq, Israel, Jordan, Kuwait, Lebanon, Libya, Morocco, Oman, Qatar, Saudi Arabia, Syria, Tunisia, United Arab Emirates, Palestine, and Yemen.
• Temporal Scale: 85 years, from 1940 to 2024.

Methodology and Data

• Models used:
  • Long Short-Term Memory (LSTM) neural network model (Python, TensorFlow/Keras) for gap-filling missing daily in-situ precipitation data.
  • Theil–Sen estimator for determining trend slopes.
  • Mann–Kendall (MK) test for assessing statistical significance of trends (p-value < 0.05).
  • Expert Team on Climate Change Detection and Indices (ETCCDI) guidelines for computing 13 precipitation indices.
• Data sources:
  • Daily observational precipitation data from 150 in-situ stations across the MENA-T region, obtained from the Royal Netherlands Meteorological Institute (KNMI) Climate Explorer platform ("precip + GTS" product).
  • Hourly ERA5 reanalysis total precipitation data with a spatial resolution of 0.25° × 0.25°, obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) Copernicus Climate Change Service.

Main Results

• ERA5 reanalysis data demonstrated good skill in reproducing observed daily precipitation, with an overall average Pearson Correlation Coefficient (R) of 0.72 (ranging from 0.56 to 0.82) across the 150 stations.
• A pronounced north–south hydroclimatic dipole in precipitation trends was identified across the MENA-T region:
  • Southern arid and semi-arid regions (e.g., Arabian Peninsula, Libya, southern Algeria, northern Egypt): Showed significant increases in consecutive dry days (CDD), indicating intensifying aridity (Sen's slope often exceeding +0.7 days/year). Declining trends were observed for annual total wet-day precipitation (PRCPTOT) and extreme rainfall indices (R85p, R95p, R99p, Rx1day, Rx5day), as well as frequency-based indices (R1mm, R5mm, R10mm, R20mm).
  • Northern coastal and mountainous zones (e.g., Türkiye, northern Iraq, Iran, northern Morocco/Algeria/Tunisia): Exhibited decreasing dry spell durations (CDD, up to -1.1 days/year) and increasing annual total wet-day precipitation (PRCPTOT, exceeding +5.8 mm/year). These regions also showed increases in extreme rainfall events (R85p, R95p, R99p, Rx1day, Rx5day, SDII) and wet-day frequencies (R1mm, R5mm, R10mm, R20mm).
• Comparative analysis revealed that in-situ data generally show stronger trend magnitudes and greater spatial variability than reanalysis, with ERA5 tending to underestimate drying trends and declines in wet-day frequency and extreme precipitation intensity, particularly in arid and semi-arid zones.

Contributions

• Provides a comprehensive, region-wide, and systematic assessment of 13 ETCCDI precipitation indices across the entire MENA-T region using harmonized methodologies for both long-term (85-year) in-situ and high-resolution ERA5 reanalysis data.
• Quantifies trends in duration, magnitude, intensity, and frequency-based precipitation indices, revealing a critical and robust north-south hydroclimatic dipole with increasing aridity in the south and intensifying extremes in the north.
• Highlights the strengths and limitations of ERA5 reanalysis in capturing regional precipitation extremes and trends compared to observational data, emphasizing the importance of multi-dataset approaches.
• Offers critical insights to support more informed water resource management, disaster preparedness, and climate adaptation strategies in one of the world's most water-stressed and climate-sensitive regions.

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Citation

@article{Othman2026comparative,
  author = {Othman, Nariman Yahya and Ayat, Berna},
  title = {A comparative analysis of long-term spatiotemporal variability in precipitation 85 year-long reanalysis and observation data from 150 stations over arid MENA-T region},
  journal = {Theoretical and Applied Climatology},
  year = {2026},
  doi = {10.1007/s00704-026-06067-4},
  url = {https://doi.org/10.1007/s00704-026-06067-4}
}