Projected Intensification and Persistence of Drought in Southeastern Anatolia, Turkey: A Multi-Index Analysis Based on CMIP6 Multi-Model Ensemble Projections

Abstract Drought is a major climatic hazard in semi-arid environments, with severe implications for agriculture, hydropower production, and socio-economic stability. This study examines Turkey’s Southeastern Anatolia Project (GAP), one of the country’s largest development programs, which encompasses nine provinces: Siirt, Gaziantep, Kilis, Adiyaman, Sanliurfa, Mardin, Diyarbakir, Batman, and Sirnak. Future drought variability in this region is assessed using multi-model ensemble projections derived from Global Circulation Models (GCMs) participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6). Daily precipitation, maximum temperature, and minimum temperature outputs from 24 GCMs are spatially standardized, bias-corrected, and evaluated using statistical performance metrics. The four best-performing GCMs are combined into ensembles for each climate variable under the CMIP6 historical experiment and the Shared Socio-economic Pathway (SSP) scenarios SSP2-4.5 and SSP5-8.5. Drought dynamics are analyzed using three complementary indices: the Standardized Precipitation Index (SPI), the Standardized Precipitation Evapotranspiration Index (SPEI), and the Palmer Drought Severity Index (PDSI). Validation indicates strong agreement with observations for the historical simulation period (1965–2014) and the initial projection decade (2015–2024), while acknowledging methodological and index-related uncertainties. Ensemble projections for the near- and late-century periods (2025–2062 and 2063–2100) indicate an increasing frequency and persistence of drought events. SSP2-4.5 exhibits greater drought severity in the near-century; in contrast, SSP5-8.5 yields more severe conditions in the late-century. While the proposed integrated multi-model, multi-index framework provides a potentially transferable tool for assessing drought risk in other semi-arid regions worldwide, the findings offer strong evidence supporting the urgent need for climate adaptation in the GAP provinces.