Simulating the Effects of Climate Change on Runoff Using the CMIP5 and CMIP6 Climate Models by SWAT Hydrological Model (Case Study: Tashk-Bakhtegan Basin)

Climate change directly affects the hydrological components and water resources and plays an important role in exacerbating potential hazards such as drought and flood. Therefore, it is necessary to study the effects of climate change on hydrological components such as runoff. In this study, the runoff in Tashk-Bakhtegan basin, as one of the most important ecological basins in the country, was investigated in terms of climate change using the SWAT model. Simulation was performed for the near future (2021-2050) by applying climate change conditions in GFDL-ESM2M and IPSL_CMA5_LR models under RCP2.6 and RCP8.5 scenarios and in GFDL-ESM4 and IPSL_CMA6_LR models under SSP1-2.6 and SSP5-8.5 scenarios. The calibration and validation results of the SWAT model using R2, NSH and RMSE indices were in the ranges of (0.70-0.99), (0.51-0.98) and (0.9-14.4 m3/s), respectively which indicated the high accuracy of calibration and validation of the model. Examination of the status of climatic variables of precipitation and minimum and maximum temperature in the conditions of climate change showed an increase in temperature (1.51-2.91 °C) for all models and scenarios and a decrease in precipitation (0.05-11.15 percent) in most models and scenarios. Simulation by SWAT hydrological model in climate change conditions showed runoff decline in all 4 stations under SSP scenarios and runoff rise in 3 stations under RCP scenarios. Given that the climate data of SSP scenarios have recently been made available, the results of this study can be useful to extend the research to the effects of these scenarios on important basins of the country and as a result of policy and planning of water resources under influence climate change.