Evaluation of Meteorological Drought Index and Climate Change Scenario on Flow Rate and Reservoir Volume of Karaj Dam

Understanding the climate and providing safe water are two critical issues in discussing climate change and water scarcity and alarm for the future.  The purpose of this study is to evaluate the SPI drought index on the trend and duration of drought in the region and its effect on river discharge and reservoir volume of the dam.  Using climate model scenarios, this trend was extracted in the future from 2030 to 2050, and its impact in the future was estimated. Therefore, SWAT software for 1994 to 2012 was used for four hydrometric stations of Gachsar, Sierra_Kelvan, Sierra_Karaj, and Pol-e-Khoab to achieve and calibrate the results of the SUFI2 algorithm in SWAT-CUP environment with appropriate bandwidth and Nash coefficients of 0.54, 0.45, 0.72, and 0.58 respectively. Also, validations for the period 2013 to 2019 were extracted 0.34, 0.38, 0.5, and 0.44, respectively. According to the results, the climate change and drought index trend indicated a decrease in river flow and increased temperature, increasing evaporation from the dam reservoir's surface. In general, the volume of the dam reservoir has decreased by about 24 to 35% based on different scenarios.  On the other hand, considering the UNESCO IWRM guidelines, examining the evolutionary trend, and changing the flow rate, it was suggested that to plan the basin and implement important policies, crisis control of three social, economic, and environmental scenarios is seriously considered in the region.