Rainfall Extreme Indicators Trend and Meteorological Drought Changes Under Climate Change Scenarios

In the current study, three optimistic (SSP1-2.6), medium (SSP2-4.5), and pessimistic (SSP5-8.5) scenarios were used to examine changes in precipitation based on the sixth phase of Coupled Model Intercomparison Project (CMIP6) in the Gorganrood watershed over two time periods: the near future (2021-2060) and the far future (2061-2100). To do this, the rainfall of 27 meteorological stations was studied. Using the RClimdex software in the R software, precipitation extreme indicators (11 indicators) were determined for different scenarios and periods, and Mann-Kendall (MK) and Sen's estimator tests were then used to detect the trend. The results showed that in the near future under SSP1-2.6, the indicators of consecutive dry days (CDD) and consecutive wet days (CWD) have a significant downward and upward trend, respectively. While in the SSP5-8.5, the indicators of maximum five-day rainfall (RX1day), CDD, number of very wet days (R95p) and total wet day precipitation (PRCPTOT) have a significant downward trend in some stations. Similarly, in the far future, in the SSP5-8.5, the trend of rainfall indicators is insignificant compared to the near future, but still a significant decreasing trend can be seen in R95p, R99p, and PRCPTOT. Z score index (ZI) values in both future periods showed that drought peaks occurred in the optimistic scenario and drought peaks occurred in the pessimistic scenario, and almost normal conditions prevailed in the intermediate scenario. The results can be effective in policies to deal with global warming and climate change.