Assessment of future meteorological droughts in Iran.

Climate change amplifies the risk of hydroclimatic extremes, posing significant challenges for arid and semi-arid regions vulnerable to temperature and precipitation variability. This study projects future meteorological drought in Iran under different climate change scenarios, focusing on two key objectives: (1) evaluating the performance of the NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) from the Coupled Model Intercomparison Project Phase 6 (CMIP6), and (2) quantifying future drought conditions using the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI). We employ a multi-model ensemble of 25 bias-corrected and downscaled General Circulation Models (GCMs) under four Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5) to project variations in temperature, precipitation, and meteorological drought occurrence in Iran for 2071-2100. The novelty of this study lies in integrating an Iran-specific evaluation of NEX-GDDP-CMIP6 with multi-timescale SPI-SPEI comparison and quantitative attribution of projected drought changes to precipitation and potential evapotranspiration (PET). Results reveal pronounced warming, especially under SSP5-8.5, exceeding 5 °C in many parts of the country by 2100. Although precipitation projections show slight increases overall, notably under SSP3-7.0, substantial regional variability persists. Projections indicate that meteorological droughts are expected to become more frequent and severe in the northwestern and southeastern parts of Iran, with SPEI indicating greater drought intensity and duration due to temperature-driven increases in PET. These findings highlight the need for climate-resilient water management and robust adaptation policies to reduce the impacts of future droughts.