Akbas et al. (2026) An Investigation of the Variability of Short-Term Drought with SPEI-Based Severity, Duration and Magnitude Parameters in a Transboundary Basin

Identification

• Journal: Pure and Applied Geophysics
• Year: 2026
• Date: 2026-01-22
• Authors: Ergun Akbas, Ramazan ACAR, Musa Eşit, Cihangir Köyceğiz
• DOI: 10.1007/s00024-025-03893-x

Research Groups

• General Directorate of State Hydraulic Works, Adıyaman, Türkiye
• Hydraulic Division, Civil Engineering Department, Munzur University, Tunceli, Türkiye
• Hydraulic Division, Civil Engineering Department, Adıyaman University, Adıyaman, Türkiye
• Civil Engineering Department, Konya Technical University, Konya, Türkiye

Short Summary

This study investigated short-term drought variability in the lower Euphrates-Tigris Basin (Türkiye) from 1963–2021 using SPEI-based severity, duration, and magnitude parameters and multiple trend analysis methods. Findings indicate a basin-wide decrease in drought severity and magnitude but an increase in duration, suggesting a shift towards longer-lasting, less intense droughts with critical implications for agriculture.

Objective

• To investigate the variability of short-term drought using severity, duration, and magnitude parameters derived from 1-month and 3-month series of the Standardized Precipitation Evapotranspiration Index (SPEI).
• To detect, categorize, and analyze the variability of drought using both graphical and statistical trend analysis methods in the lower Euphrates-Tigris Basin within Türkiye.
• To provide a robust understanding of drought dynamics under climate change conditions and generate reliable scientific evidence for sustainable water management strategies.

Study Configuration

• Spatial Scale: The lower part of the Euphrates-Tigris Basin (LTEB) within Türkiye, covering approximately 54,696 square kilometers (7% of Türkiye). The study focused on four meteorological stations in the Southeast Anatolian region (Mardin, Batman, Şırnak, Hakkari).
• Temporal Scale: Monthly data for the period 1963–2021 (59 years).

Methodology and Data

• Models used:
  • Drought Index: Standardized Precipitation Evapotranspiration Index (SPEI) at 1-month and 3-month time scales. Potential evapotranspiration (PET) was calculated using the Thornthwaite equation.
  • Trend Analysis Methods: Mann–Kendall (MK) test, Spearman’s Rho (SR) test, Sen’s Slope Estimator (SS), Şen Innovative Trend Analysis (Şen-ITA), and Combination of Wilcoxon Test and Scatter Diagram (CWTSD).
• Data sources: Monthly total precipitation and monthly mean temperature data for LTEB basin stations obtained from the General Directorate of Meteorological Department.

Main Results

• "Near normal" conditions were the most frequent across all stations and time scales, ranging from approximately 63% to 67%.
• SPEI-3 generally indicated a higher prevalence of "Moderately wet" and "Very wet" conditions compared to SPEI-1, which was more sensitive to "Extremely dry" and "Severely dry" categories.
• A notably severe drought event was observed across all stations at the very end of the record (2021) for both SPEI-1 and SPEI-3.
• More severe droughts were observed in the eastern part of the basin compared to the western part.
• Across the basin, drought severity and magnitude showed a decreasing trend, while drought duration showed an increasing trend according to both statistical and graphical analyses.
• The increase in duration suggests a shift from short-term to longer-term drought periods, which has significant implications for agricultural planning.
• Stations 17275 and 17950 exhibited statistically significant decreasing trends in drought severity and magnitude, and significant increasing trends in drought duration.
• Stations 17282 and 17920 generally showed no statistically significant trend for drought indicators, though station 17920 showed a graphical increasing trend for SPEI-3 drought duration.
• Innovative Trend Analysis (ITA) graphs demonstrated a prevailing shift toward greater drought frequency, particularly at the 3-month time scale, and a decline in wet category occurrences.

Contributions

• This study presents a novel comprehensive approach by simultaneously examining drought characteristics (duration, severity, and magnitude) using multiple complementary trend analysis methods (Innovative Trend Analysis (ITA), Wilcoxon rank-sum test, and Spearman’s rho trend).
• It addresses a significant gap in the literature by being the first to comprehensively analyze these three critical drought characteristics using this specific combination of trend detection techniques across different time scales (SPEI-1 and SPEI-3).
• The integrated approach provides a more robust understanding of drought dynamics under climate change conditions and generates reliable scientific evidence to support sustainable water management strategies in the region.

Funding

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

Citation

@article{Akbas2026Investigation,
  author = {Akbas, Ergun and ACAR, Ramazan and Eşit, Musa and Köyceğiz, Cihangir},
  title = {An Investigation of the Variability of Short-Term Drought with SPEI-Based Severity, Duration and Magnitude Parameters in a Transboundary Basin},
  journal = {Pure and Applied Geophysics},
  year = {2026},
  doi = {10.1007/s00024-025-03893-x},
  url = {https://doi.org/10.1007/s00024-025-03893-x}
}