Trend behavior of flow time series in the upper euphrates basin: evaluation on a monthly, seasonal, and annual scale

Global climate change has significant impacts on the hydrological cycle, leading to significant changes in hydrometeorological parameters such as precipitation regimes, evaporation, runoff, and groundwater levels. In this context, long-term analysis of streamflow trends is of great importance for the sustainable management of water resources. This study aimed to determine trend changes in hydrological time series using average 60-year streamflow data from three streamflow observation stations in the Euphrates Basin. Both classical and innovative statistical analysis methods were used within the scope of the study. The applied methods include the Innovative Şen Trend Method (ITA), Şen Trend Slope (ITAS), Mann-Kendall (MK), Spearman's Rank Correlation (SRC) and Sequential Mann-Kendall (SQMK). Using these methods, the direction of statistically significant trends in streamflow data (increasing, decreasing, or stationary), the magnitude of the trends, and possible change points over time were analyzed. The results reveal the spatial and temporal distribution of hydrological variability in the Euphrates Basin and contribute to the development of water management strategies at the basin scale and the assessment of the regional impacts of climate change. Keywords: Trend analysis, Flow data, Upper Euphrates basin.