Flood Frequency and Temporal Variability Analysis of Yeşilırmak Basin Under Homogeneity and Change Point Criteria

In this study, flood frequency analysis was carried out for the Yeşilırmak Basin, Türkiye, using annual maximum flow series derived from daily discharge data recorded at 14 gauging stations. Homogeneity of the series has been examined by the tests of Pettitt’s, Standard Normal Homogeneity, Von Neumann Ratio, Buishand Range, and Cumulative Deviation. Change points were detected by Pettitt’s Test and the Standard Normal Homogeneity Test, and non-homogeneous series were divided accordingly. Temporal variabilities were investigated using the tests of Mann–Kendall, Spearman’s Rho and Sen’s Slope. Flood quantiles corresponding to return periods were estimated with the most appropriate probability distributions based on goodness-of-fit tests. Results indicated that 11 stations were homogeneous, while three stations were non-homogeneous in which 1993 was identified as a common change point year. Trend results revealed predominantly non-significant decreasing trends and negative trend slopes in the series. Gamma and Weibull distributions showed superior performance as most appropriate distributions. Due to divided series, flood magnitudes have been investigated in two cases. The first case has given larger flood magnitudes than the second case. In both cases, the stations in upper middle of the basin have higher flood magnitudes that contain more flood risk in the basin.