Evaluation of annual total precipitation in the transboundary Euphrates–Tigris River Basin of Türkiye using innovative graphical and statistical trend approaches

Abstract

The Euphrates–Tigris River Basin (ETRB), one of the largest river basins in the Middle East, is also among the most risky transboundary basins in the world. ETRB has a critical importance for the region both politically and economically due to its location. Evaluating the increasing regional impacts of climate change is even more important for the sustainable management of water and soil resources, especially in transboundary basins such as ETRB. Türkiye is one of the most important riparian countries of the ETRB and the Türkiye part of ETRB constitutes the headwater of the basin. In this study, the temporal variability of the annual total precipitation data for the period 1965–2020 of eighteen stations located in the Türkiye part of the ETRB was investigated. Classical Mann–Kendall (MK) test was used to statistically determine the monotonic trend of precipitation. In addition to the MK method, analyses were carried out with three innovative trend methods, which have the ability to interpret trends both statistically and graphically. These innovative trend methods are Şen innovative trend analysis (Şen-ITA), Onyutha trend test (OTT) and trend analysis with combination of Wilcoxon test and scatter diagram (CWTSD). The results obtained show that there is a decreasing trend in annual total precipitation in ETRB according to all trend methods generally used for the examined period. In addition, the results obtained from the relatively new OTT and CWTSD methods show strong consistency with the results of the other two methods. The advantages such as performing numerical and visual trend analysis with innovative OTT and CWTSD methods, identifying trends in low–medium–high value data and detecting sub-trends have shown that these methods can be used as an alternative to the widely used MK and Şen-ITA.

Comparison of Innovative Trend Analysis Methods for Hydrometeorological Parameters in the Karasu Sub-Basin

“…Here, n, xi, yi, and 𝑥̅ represent the number of data in each subseries, the data value at the time i in the first ordered subseries, the data value at the time i in the second ordered subseries, and the mean of the first subseries. The negative (positive) value of DSen-ITA shows a decreasing (increasing) trend [18,20,29].…”

“…According to this method, statistical trend evaluation is made to the Wilcoxon test. The calculation procedure of the Wilcoxon test is available in various studies in the literature and is not included here [20,23]. To the ZWilcoxon value obtained as a result of the application, the trend evaluation is made by comparing the Zcritic value at the α significance level obtained from the standard normal distribution table [20,23].…”

“…Considering the distribution of the marked points according to the 1:1 straight line, five different trend evaluations can be made monotonic increasing trend, monotonic decreasing trend, non-monotonic increasing trend, non-monotonic decreasing trend, and no trend. See references for details of the method [20][21]. Şen-ITA trend indicator (DSen-ITA) is calculated by Equation 5.…”

“…Mann-Kendall trend analysis is the most widely used statistical trend method [16][17][18]. The Innovative Şen Trend method, on the other hand, is a method that has been used for about ten years in the analysis of the variability of hydrometeorological parameters and offers the opportunity to evaluate trends both graphically and statistically [18][19][20][21][22]. In recent years, innovative graphical trend methods have been used.…”

Hydrological Droughts in the Eastern Mediterranean Basin Using Hybrid Trend Analysis Methods

“…The MK test, alongside other methods such as the Innovative Trend Analysis (ITA) method, has been applied to various basins worldwide, providing valuable insights into spatial and temporal changes in river systems. For instance, the trend analyses conducted in the Tigris and Euphrates River basins have revealed signi cant trends in stream ow, emphasizing the effects of climatic and environmental changes (Buyukyildiz, 2023;Yurekli, 2023). These studies underscore the signi cance of trend analysis in river systems as a critical tool for policy-making and sustainable water resource management.…”