Comparison of the outcomes of the CMIP5 and CMIP6 reports on the trends of climatic parameters affecting almond growth: A case study in Birjand County

In this study, we aimed to predict the trends of climatic parameters affecting almond growth from 2021 to 2100. We utilized the IPSL-CM5A-LR and GFDL-ESM2M models from the CMIP5 report, as well as the GFDL-ESM4 and IPSL-CM6A-LR models from the CMIP6 report. These models were selected based on their high coefficient of determination (r^2) with temperature and precipitation data from the Birjand station, outperforming the other 10 models. Kendall's rank correlation test results revealed that the average, maximum, and minimum temperatures exhibited an increase of over 3 degrees Celsius, while precipitation showed a decreasing trend. These findings suggest a prevalence of dry conditions during the study period from 2021 to 2100. Furthermore, the climate models showed that the RMSE (Root Mean Square Error) and MAD (Mean Absolute Deviation) values for temperature in all the examined models were below 1.322. The GFDL-ESM2M model displayed the lowest RMSE and MAD values, with numerical values of 1.023 and 0.997, respectively. However, all models' RMSE and MAD values for precipitation were above 10. Overall, the CMIP6 models (RMSE for temperature and precipitation: 1.156 and 14.463, MAD for temperature and precipitation: 1.139 and 12.583) performed better in predicting temperature and precipitation in the study area, exhibiting lower mean errors compared to the CMIP5 models. The only exception was the MAD value for precipitation 11.703 (RMSE for temperature and precipitation: 1.172 and 13.479, MAD for temperature and precipitation: 1.140 and 11.703). Finally, due to the increase in minimum and maximum temperatures and decrease in precipitation, the future conditions of the crops are facing a challenge.