Effect of Climate Change on Precipitation Patterns in an Arid Region Using GCM Models: Case Study of Isfahan-Borkhar Plain

Climate change has major implications for a wide range of natural processes and phenomena, with precipitation patterns particularly sensitive to changes in atmospheric forcing. The arid and semiarid regions of the world, such as Iran, have been affected by declining precipitation. The Isfahan-Borkhar plain in the central region of Iran is one of the areas that has been damaged due to the decrease in rainfall in recent years, and many agricultural lands in this area have already been laid. In this study, five general circulation models (GCM) (MIROC5, MIROC-ESM, MIROC-ESM-CHEM, MRI-CGCM3, and NorESM1-M) for the UN's Fifth Assessment Report (AR5) on climate change were used to assess future changes to precipitation patterns for the Isfahan-Borkhar plain. These models were implemented using three emission scenarios: the representative concentration pathway (RCP)2.6, RCP4.5, and RCP8.5. The period for application of these models is from 2020 to 2044. The GCM models were weighted based on the comparison of their output in the historical period with observational data. Based on the weight assigned to each model, the models were combined and then downscaled using the LARS-WG model. The weighting results showed that the MIROC5 model was the most accurate model among all GCM models. The accuracy of this model in September was more than that of the other months. The results also showed that precipitation in all emission scenarios would decrease, which was higher in the RCP8.5 emission scenario than in other RCP's and would have the highest drop in precipitation in August. As it is known, in the RCP2.6 and RCP4.5 emission scenarios, the highest precipitation reduction in winter is expected to be 7.2% and 17%, respectively. Also, for the RCP8.5 emission scenario, the highest precipitation in the spring would be 32.7%. The lowest seasonal precipitation reduction will occur in all emission scenarios in autumn, which will be 3%, 6.9%, and 14.4% in the RCP2.6, RCP4.5, and RCP8.5 emission scenarios, respectively.