Trend Analysis of Potential Evapotranspiration Data of Some Stations in the Tigris Basin

Determining trends in potential evapotranspiration (PET) values is of great importance in climate change and drought management, more efficient management of agricultural water resources, and optimal design of irrigation planning. This study carried trend analyses of seasonal and annual PET values calculated between 1964 and 2017 for Batman, Cizre, Diyarbakır, and Hakkâri meteorological stations located in the Tigris basin. Şen's Innovative Trend Analysis (ITA) and Mann-Kendall Rank Correlation (MKRC) methods were used to determine the trends. Thornthwaite methodology, which is frequently used in the calculation of PET values, is simple and requires less data. At the end of the research, according to the ITA method, while the PET data of the stations selected in the basin generally had statistically significant increasing trends, statistically significant decreasing trends were determined for the Diyarbakır station in the spring and winter seasons. According to the MKRC test, there are significant increases in PET values at station locations, except for winter. In addition, although the ITA and MKRC tests overlap to a large extent, the increasing trends detected with ITA at some stations could not be determined by the MKRC test. The results obtained provide important information to decision-makers in planning and efficient use of agricultural water resources and developing adaptation and mitigation strategies to combat the effects of global warming.