The evaluation of monthly precipitation and average temperature by using innovative graphical and statistical trend approaches: Palu station example

Abstract

Abstract Climate change occurring worldwide due to global warming affects rainfall, flow, humidity and temperature, etc. in many regions. It has begun to significantly change the regimes of hydro-meteorological parameters. It is extremely important to analyze the future changes of these parameters, which significantly affect the management of water resources, ecosystems and agricultural activities. In this study, the temporal variability of monthly total precipitation (1965–2012) and monthly average temperature (1965–2020) data of Palu station located within the borders of Elazığ province in Turkey was investigated. Mann-Kendall (MK) and Spearman's Rho (SR) test statistics were used to statistically determine the trends of temperature and precipitation data. In addition to these methods, analyzes were carried out with three innovative trend methods that are capable of interpreting trends both statistically and visually. These innovative trend methods are Innovative Polygon Trend Analysis (IPTA), Innovative Şen Test (Şen-ITA) and trend analysis with the combination of Wilcoxon test and scatter diagram (CWTSD). In addition, precipitation and temperature data were subjected to regression analysis separately and sets of equations were obtained and the decrease-increase amounts were determined in mm and ⸰C. In particular, the IPTA method was applied separately for the arithmetic mean and standard deviation, and the transitions between the increasing and decreasing regions of the trends on a monthly basis were determined and the slopes and lengths of the trends resulting from these transitions were calculated. With the application of the IPTA method, an increasing trend in some months and a decreasing trend in other months were detected for the two parameters. In addition, when the results of precipitation and temperature data were examined, it was seen that there was no single or regular polygon in the IPTA graphs, so both parameters varied over the years and did not exhibit a homogeneous behavior. In the MK test, SR test, Wilcoxon test statistics, Şen-ITA and NO-ITA methods, apart from some months in which increasing and decreasing trends were detected, months in which no trend could be detected, that is, there was no trend, were also observed. When the results obtained from the analysis of two parameters from the relatively new CWTSD method are examined, they show strong consistency with the results of the MK test, SR test and Şen-ITA methods. Advantages such as performing numerical and visual trend analysis with the CWTSD method and determining the trends of data with low-medium-high values have shown that this method can be used as an alternative to the MK test, SR test and Şen-ITA methods that are widely used in the literature. Finally, the IPTA method was evaluated to be more sensitive in determining trends on a monthly basis compared to other methods used in the study..