A Dual-Method Evaluation of Long-Term Precipitation Changes in Türkiye’s Eastern Black Sea Basin

In this study, the long-term and seasonal precipitation dynamics of the Eastern Black Sea Basin were investigated using monthly total precipitation data from six meteorological stations for the period 1994–2024. Two contemporary trend analysis techniques—the Multi-Risk Level Identification (MRLI) method and the Trend Polygon Star Concept Method (TPSCM)—were applied to provide a comprehensive evaluation of precipitation behavior. The MRLI approach identified increasing, decreasing, or stable trends across a range of risk percentiles by determining critical precipitation thresholds from best-fitting theoretical distributions validated through the Kolmogorov–Smirnov (K-S) test. The results revealed substantial spatial variability: while Giresun exhibited consistently increasing trends at all risk levels, Artvin and Trabzon showed mixed behavior with both upward and downward tendencies depending on the percentile. In addition, a basin-wide evaluation indicated that approximately 65% of the overall trends were increasing, whereas 35% displayed decreasing tendencies, highlighting a general intensification of precipitation conditions in the region. The remaining stations showed diverse responses across low-, medium-, and high-risk classes. The TPSCM method offered further insights into intra-annual variability by categorizing month-to-month precipitation transitions into four directional regions representing shifts between early and late sub-periods. The spatial distribution of these regions varied considerably among provinces, indicating notable temporal changes in seasonal rainfall structures. Overall, the combined application of MRLI and TPSCM enabled a detailed assessment of both long-term and seasonal precipitation characteristics, providing a robust basis for advanced hydrological planning and climate adaptation strategies in the Eastern Black Sea Basin.