Drought Trends in the Arabian Peninsula Using SPEI and SPEDI Indices and their Implications for Climate Adaptation

Recent decades have witnessed intensifying drought across the Arabian Peninsula, yet scientists poorly understand whether precipitation deficits or increased potential evapotranspiration (PET) drive this intensification. This study employs the Standardized Precipitation Evapotranspiration Index (SPEI) and Standardized Precipitation Evaporation Differential Index (SPEDI) at 3, 6 and 12-month timescales to assess drought across the Arabian Peninsula from 1975 to 2024 using ERA5 Land reanalysis data validated against observed meteorological stations. We isolated each variable’s contribution through diagnostic scenarios, holding either PET or precipitation at climatological means while varying the other. Validation results demonstrated exceptional ERA5 Land performance for temperature variables (mean R = 0.99, NSE > 0.89) and adequate performance for precipitation (mean R = 0.72, NSE = 0.48). Temporal analysis revealed intensifying multi-year droughts, with drought-affected areas increasing by 20 to 133 percent between the first (1975–1999) and second (2000–2024) study halves across all zones. Frequency Innovative Trend Analysis (F-ITA) confirms a systematic decline in wet anomalies and increases in drought frequency, with the southwestern zone experiencing the most pronounced shift, where mild drought rose from 14.6 percent to 37.6 percent for SPEI 12. The SPEI scenarios revealed that PET contributes 68 to 77 percent of drought trend variability across all climatic zones, while precipitation contributes only 23 to 30 percent. When PET is held constant (PETclm), significant drying trends largely disappear; conversely, when precipitation is held constant (Prclm), drought intensification exceeds observed trends, confirming thermodynamic forcing as the primary driver. The findings demonstrate that rising temperatures, rather than precipitation deficits, will determine future drought severity in the Arabian Peninsula, necessitating fundamental shifts in water resource management from precipitation-centric approaches toward strategies explicitly addressing temperature-driven PET.