Projection and Assessment of precipitation and temperature changes by the CMIP6 models (Case study: Hashemabad Gorgan station)

In recent decades, with the trend of warmer weather and heavy rains caused by climate change, events such as floods or droughts have clearly increased in many parts of the world. Therefore, it seems necessary to predict climate change by models to know the future conditions and manage water resources in line with adaptation.

The aim of the current research was investigation and evaluation of climate change forecasting on Hashemabad Gorgan synoptic station which located in the Qarasu basin of Golestan province. Precipitation data, maximum temperature and minimum daily temperature of the studied station were obtained from the Meteorological Department of Golestan province and the data of 1990-2014 were considered as the base period. The homogeneity of the observational data checked by using four tests of Standardized Normality Homogeneity (SNH), Bishand Range (BHR), Pettit (PET), Van-Neumann Ratio (VON) provided in the trend package in RStudio environment. Further, by examining the statistical tests of correlation coefficient (R), Root Mean Square Error (RMSE), Mean Absolute Error (MAE) and Kling Gupta (KGE) among the three models MIROC-ES2L, EC-Earth3-Veg-LR and EC- Earth3-CC From the set of CMIP6 models, the EC-Earth3-CC model was selected as the best model at this station. Straw scaling was performed using the linear scaling method (LS) by Climate Model data for Hydrologic modeling (CMHyd) software. Projection was made for three statistical periods of the near future (2026-2050), medium (2051-2075) and long-term (2076-2100) according to two intermediate (SSP2-4.5) and very pessimistic (SSP5-8.5) scenarios. Also, the trend of observational data and future periods was determined by the non-parametric Mann-Kendall test and age slope.

The results of the statistics parameter’s error showed that the models do not have a good ability to estimate precipitation and have high uncertainty, but they will have good results for temperature. The results of the investigation of the average monthly changes of the precipitation variable in all three future periods, except for the SSP2-4.5 scenario in the middle future, have a decreasing trend compared to the observation period, and this decrease in the SSP2-4.5 scenario is more in the near future than in the SSP5-8.5 scenario and less in the distant future. The average changes of the maximum temperature and the minimum temperature in all three future periods have an increase compared to the observation period, and this increase is more evident in the two middle and far future periods in the SSP5-8.5 scenario than in the SSP2-4.5 scenario. It can also be said that the increase in the maximum temperature variable for both scenarios will be higher than the minimum temperature in all three future periods. The highest increase in maximum temperature according to the SSP2-4.5 scenario compared to the observation period in all three future periods in July and the lowest increase respectively in the near, middle and far future period in Jan, Dec and Jan and according to the SSP5-8.5 scenario the highest increase respectively in The months of March, July and August and the lowest increase in all three periods was observed in January. The highest minimum temperature increase according to the SSP2-4.5 scenario compared to the observation period in the near, middle and far future respectively in July, Feb and Aug and the lowest increase respectively in April, Dec and Jan and according to the SSP5-8.5 scenario the highest and lowest increase. The close period is observed in Feb and Jan, and in the other two periods in August, and the highest and lowest increases of both middle and far periods are observed in August and April, respectively. The results of examining the situation of SSP2-4.5 scenario, the monthly values of precipitation in all the months of the future period except April, the monthly values of the maximum temperature of all the months of the three future periods and the minimum temperature of all the months of the three future periods except of May and June of the near period and The distant future Jan has no significant trend at the 95% and 99% confidence levels. The significant trend status of the climatic parameters of the SSP5-8.5 scenario has increased in all three future periods compared to the SSP2-4.5 scenario.

Finally, the results of this research showed that the air temperature in the desired station is getting warmer and it can affect the quality and quantity of water resources, so it is suggested to investigate the effect of climate change on runoff in future researches.