Trend analysis of annual instantaneous maximum flows in Turkey river basins

Hydrological extremes (floods and droughts) have a crucial impact on society and ecosystems and are expected to increase in frequency and severity with climate change. Detection of significant changes (trends) in extremes plays an important role in planning, design and management of water resources. This study presents a comprehensive evaluation of trends in Annual Instantaneous Maximum Flows (AIMF) from 153 gauge stations located in 26 river basins, Turkey. Two traditional non-parametric trend tests, namely Mann-Kendall and Spearman Rho, were used to quantify significance of temporal trends while Sen's Slope method was applied to determine magnitude of the trends. According to the result of the Mann Kendall trend test, there was a statistically decreasing trend in the AIMF data of 57 stations, while 6 stations showed an increasing trend. The Spearman Rho test identified increasing trends at the same stations as the Mann Kendall test and detected a decreasing trend in the AIMF data of 59 stations. Moreover, the recently proposed Şen's trend method, which provides more detailed assessment of trends in different clusters (low, medium and high), was applied to AIMF series and its results were compared with traditional tests. Although there was generally good agreement between the tests results, the Şen's method showed indications of more decreasing and increasing trends which can be a sign of hazardous circumstances both in the human lives and natural environments.