Seasonal Wilcoxon and Scatter Diagram Combination Trend Test

Climate change, one of the biggest problems of the last century, is of great concern. It is essential and common to examine the impacts of climate change as a holistic trend for different climatic and hydrological parameters with periodicity. However, considering the periodicity character of monthly, weekly, etc., is particularly important for analyzing and understanding seasonal trends. This is because seasonal trends help manage and regulate irrigation and agricultural activities and water resource systems. This study proposes the seasonal Wilcoxon and scatter diagram combination trend test (SWTT) method as an alternative to the seasonal Mann Kendall (SMK) method. This method is based on the combination Wilcoxon test and scatter diagram (CWTSD) trend test which assesses holistic trends. The data utilized for this study came from three sources: flow records from the Danube River, Romania, temperature records from Oxford, UK, and precipitation records from Kobe, Japan, to compare SWTT and SMK methods. The SWTT method shows very similar trends to the SMK, but the SWTT method takes a step forward because it is based on a graphical method providing a visual overview of seasonal trends. The SWTT can also be used as a regional trend test in the same way that the SMK method is used as a regional trend test by using station data instead of seasons The r-codes of the proposed method and the sample dataset are available at the related link.