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 it remains unclear whether precipitation deficits or increased potential evapotranspiration (PET) are the dominant driver of this intensification. This study employs the Standardized Precipitation Evapotranspiration Index (SPEI) and the recently introduced Standardized Precipitation Evaporation Differential Index (SPEDI), which integrates SPI and EDDI to enhance sensitivity to rapid-onset, heat-driven drought. Both indices were calculated at 3-, 6-, and 12-month timescales for the Arabian Peninsula from 1975 to 2024 using ERA5-Land reanalysis data validated against observed meteorological stations. Driver contributions were isolated through diagnostic SPEI scenarios (PETclm and Prclm), in which PET or precipitation was alternately fixed at its monthly climatology while the other variable varied freely. Results reveal intensifying multi-year droughts, with drought-affected areas increasing by 11–156% between 1975 and 1999 and 2000–2024 across climatic zones and timescales. Frequency-Innovative Trend Analysis (F-ITA) confirms a systematic decline in wet anomalies and increases in drought frequency, with the southwestern zone showing the most pronounced shift. In this zone, mild drought frequency increased from 14.6% to 37.6% for SPEI-12, while SPEDI-12 showed an even stronger increase from 16.3% to 44.1%, highlighting SPEDI’s added sensitivity to concurrent precipitation deficits and elevated evaporative demand. Diagnostic scenarios indicate that PET contributes 68–77% of drought trend variability across climatic zones, whereas precipitation contributes only 23–30%. When PET is held constant, significant drying trends largely weaken or disappear; conversely, when precipitation is held constant, drought intensification exceeds observed trends, confirming thermodynamic forcing as the primary driver. The findings demonstrate that rising temperature-driven evaporative demand, rather than precipitation deficits alone, will increasingly determine drought severity in the Arabian Peninsula, requiring a shift from precipitation-centric water management toward adaptation strategies that explicitly address PET-driven drought intensification.