Projection of Precipitation Changes in Southern Coast of Caspian Sea at the End of 21st Century using Different RCPs

Precipitation is a major component of the hydrologic cycle and its prediction is of great importance in many studies such as environmental and Land use planning. Therefore, in this study, prediction of precipitation changes in the southern coast of the Caspian Sea as the most productive region of the country was investigated. For this purpose, HadGEM2 model data were affected by three RCPs (RCP2.6, RCP 4.5 and RCP 8.5) using LARS-WG6 downscaling model and rainfall variations over three different time periods (2021-2050, -2051-2080 and 2081-2100) compared to the baseline period (1989-2018). For calibration and validation of the LARS-WG model, T and F tests and also MAE, MSE, RMSE and R2 indices were used. The results of the performance evaluation of the downscaling model show acceptable and high accuracy of this model in different stations studied. The results of the prediction also show that the average precipitation in the period (2021-2050) will decrease by 0.2% on average the southern coast of the Caspian Sea. But precipitation in the periods 2051-2080 and 2081-2100, will increase 5.4% and 10.7%, respectively. Overall, precipitation on the southern coast of the Caspian Sea will increase by an average of 5.7% by the end of the 21st century, with the highest rate being at Gorgan Station at 12.2% and the lowest at Babolsar station is up 0.3% from base period. Also, the lowest and highest precipitation variations in the study area were estimated based on RCP 8.5 and RCP 2.6 scenarios in each of the three periods study.