Long-term drought assessment and climate change signals in Türkiye using SPI, SPEI and trend analysis (1930–2024)

Drought is a complex and multidimensional phenomenon influenced by both precipitation variability and temperature-driven processes, particularly under evolving hydro-climatic conditions. A comprehensive assessment of long-term drought dynamics across Türkiye is presented using multi-timescale Standardized Precipitation Index (SPI) and Standardized Precipitation–Evapotranspiration Index (SPEI) based on data from 21 representative cities across seven geographical regions. Drought variability was evaluated at 1-, 3-, 6-, and 12-month accumulation periods, while long-term trends and regime shifts were analyzed using the Mann–Kendall test, Sen’s slope estimator, and the Pettitt test. The results indicate that short-term drought variability is dominated by high-frequency fluctuations, whereas longer accumulation periods, particularly at the 12-month scale, capture more persistent and spatially coherent drought patterns. At the 12-month scale, statistically significant trends were detected in a considerable proportion of stations, with SPEI indicating more widespread and spatially consistent drying patterns compared to SPI, which remains spatially heterogeneous and often statistically weak. These findings highlight the increasing role of temperature-driven evapotranspiration in intensifying drought conditions. Change-point analysis revealed that all stations experienced at least one statistically significant regime shift, with most change points clustering between the 1950s and early 2000s, indicating pronounced non-stationary hydro-climatic behavior. Teleconnection analysis further shows that drought variability is partially influenced by large-scale atmospheric circulation patterns, with statistically significant relationships ( p < 0.05) identified in several regions, particularly for the North Atlantic Oscillation (NAO), while the El Niño–Southern Oscillation (ENSO) shows more spatially variable and moderate effects. Overall, the results demonstrate that drought dynamics in Türkiye are governed by the combined effects of precipitation variability, temperature-driven processes, and atmospheric circulation patterns. The combined use of SPI and SPEI with trend, change-point, and teleconnection analyses provides an integrated basis for interpreting long-term drought variability and may inform climate adaptation, water resource management, and drought risk assessment.