Analysis of hydrological drought trends in the GAP region (southeastern Turkey) by Mann-Kendall test and innovative sen method

Abstract

The analysis of drought trends plays a significant role in the efficient water resource management, especially in arid and semi-arid regions. Assessing the drought trends by drought indices, of which the Standardized Precipitation Index (SPI) is the most popular, is a reasonable way, because the drought indices measure the climatic anomalies through their severity, duration and frequency. In this study, the possible hydrological drought trends in the GAP region (Southeastern Turkey) were investigated by the use of 12- and 24-month SPI series. The SPI series were determined by 48-year-long (1970-2017) monthly precipitation data monitored at nine selected stations (Mardin, Adiyaman, Batman, Diyarbakir, Siirt, Şirnak, Gaziantep, Kilis and Şanliurfa) in the GAP region. In the analyses, a recent graphical trend detection method entitled Innovative Şen Metod (ISM) and Mann-Kendall trend test (MK) were used. The ISM has non-parametric basis without any restrictive assumption, moreover, its application is rather simple when compared with the other trend identification methods. The ability to identify the trends of low, medium and high values of a series is the innovative side of the ISM. Since the significance test is a crucial factor to identify the possible trends scientifically, the results were statistical tested at the 0.05 significance level in the methods. The ISM and MK test both revealed that, Mardin is the most vulnerable province in the region, due to the significant decreasing trend, which determined by 12-month and 24-month SPI values. Şanliurfa, Kilis, Siirt, Diyarbakir and Batman are second order drone prone provinces. In accordance with the results of the ISM, there is an increasing trend in normal and wet conditions in Gaziantep, Şirnak and Adiyaman. Specifically, the results highlight that the central of the GAP region has a tendency toward the heavier droughts in the future. It is also concluded that the ISM is a valuable tool with its simplicity as well as the inherent properties to deduce qualitative information.