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.