Trend analysis of monthly streamflows using Şen's innovative trend method

Trend analysis of monthly mean streamflows is essential for better water resources management and planning. In this study, Mann Kendall (MK), Sen's method and Sen's innovative trend method (ITM) were employed in order to examine the possible trends of monthly streamflows obtained from nine stations from three basins (Yakabasi and Derecikviran in Western Black Sea Basin; Durucasu, Sutluce, Kale and Gomeleonu in Yesilirmak Basin; Simsirli, Tozkoy and Topluca in Eastern Black Sea Basin) located in Black Sea Region of Turkey. Based on the MK, streamflow data of Tozkoy Station which is located in western part of the Eastern Black Sea Region showed a significantly increasing trend while a significantly decreasing trend was found for the Yakabasi, Derecikviran, Durucasu and Sutluce stations which are situated in western part of the Black Sea Region. According to the Sen's trend method, a significantly decreasing trend was seen in Durucasu, Sutluce, Yakabasi and Derecikviran stations while Tozkoy station showed significantly increasing trend. According to the ITM, low-medium values of Tozkoy Station indicated slightly increasing trend while low and medium streamflow values of Yakabasi, Derecikviran, Durucasu and Sutluce stations showed a decreasing trend. High streamflow values of Derecikviran and Sutluce stations showed a decreasing trend while corresponding values of Yakabasi, Simsirli and Tozkoy stations indicated an increasing trend. It was showed that trends of low, medium, and high data can be easily identified by ITM which has some advantages (having no assumption such as serial relationship, non-normality, and, test number) over the Sen's method and Mann-Kendall test.