Procedure for detecting drought trends using Şen’s innovative trend analysis methodology

The increasing occurrence of drought has negative effects on water resources. To prevent these negative effects, it is of great importance to know drought trends over time. Many methods are used in the literature to determine the severity of drought, one of which is the standard precipitation index (SPI), which is calculated based on precipitation data. The SPI method was chosen in this study because it is widely used in the literature for its simplicity, flexibility and effectiveness in characterising drought duration and intensity. There are different classifications of drought severity in the SPI method, so it is very important to know the individual trends for each classification. Classical trend detection methods (such as the Mann–Kendall method) require a separate analysis for each drought classification. However, using Şen’s innovative trend analysis, it becomes possible to determine the trends for all drought classifications on a single graph. In this way, the change of drought events over time can be easily determined for all drought classifications.