Joint analysis of drought affected by climate change in Zarinehrood watershed, Iran, using copula functions

In this study, to analyze the frequency of meteorological drought characteristics under the influence of climate change for the future period, copula functions were used. In this regard, SPI index and copula function were used in Zarinehrood watershed, Iran during the base period, and based on the CanESM2 predictors in the period of 2020–2100 on a monthly scale. In the first step, SPI values were extracted for the studied stations that the results showed that 45% and 8% of the studied period were prone to precipitation deficit and severe drought, respectively. In the next step, joint frequency analysis of drought characteristics based on Frank's copula and marginal distributions was performed. The results of examining the simulated values indicated that the multivariate regression model had a higher than 91% efficiency in the multivariate simulation of precipitation affected by the CanESM2 predictors. The results indicated that in the RCP8.5, average precipitation decreased by 20–50%. The presented results led to the presentation of the curves of the joint probability of occurrence in the region, which estimate the regional characteristics of drought with different probabilities. This approach was presented in both base (1959–2010) and future (2010–2100) periods. In general, the results indicated that by maintaining the current trend and not managing greenhouse gases, more severe droughts may occur in the study area. The results of joint probability analysis of the meteorological drought severity-duration paired variable in the future statistical period also showed that the drought duration as well as the probability of occurrence of drought increased compared with the RCP2.6 scenario.