Today, global climate change has made itself widely evident. In the planning of water resources, it is of great importance to determine certain parameters, such as precipitation and flow, for the preparation of future projects. In our study, we tried to analyze the streams in the Western Mediterranean Basin of Turkey monthly and annually. Applying Mann-Kendall trend test, it was tried to observe whether a trend changed or not, in the safety range of 95%. Moreover, scatter diagrams are created to determine the slopes of increase and decrease on the trend-line, and to foresee the flow-rates. Eventually, the trends for each station are determined plotting Sen diagrams, and these trends' compliance with Mann-Kendall test is evaluated. According to the results, some serious decreasing trends are observed in all stations both annually and monthly. Besides, the trend changes occurred especially in summer when the amount of rainfall was very low and almost all of the flows of rivers were provided by underground sources. Moreover, it was discovered that there is a strong correlation between Sen test and Mann-Kendall trend analysis. The angles between x-axis and trend-lines in Sen diagram test were analyzed, and angles less than 36 degree were statically found to stand for a strong trend change.