Projection of climatic variables of temperature and precipitation using CMIP6 models outputs under SSP scenarios (Case Study: Shoor river catchment area)



Abstract

Projection long-term changes in meteorological variables is important in climate change studies. accordingly, the objective of this study is to project long term changes in key climatic variables namely temperature and precipitation in the Shoor river catchment area located in Khuzestan Province using CMIP6 model outputs under extreme (SSP) scenarios. findings from the Mann–Kendall trend analysis revealed a statistically significant upward trend in maximum, minimum, and annual temperatures, whereas precipitation showed a downward trend. furthermore, the outputs of the CanESM5 model suggest that maximum temperature, minimum temperature, and daily precipitation are projected to increase during the 2015–2050 period under extreme SSP scenarios, relative to the baseline period.



Introduction

Climate fluctuations are considered sinusoidal variations in climatic parameters on global or regional scales and are regarded as specific climate patterns. these fluctuations occur in temperature, precipitation, or other climatic parameters and unfold over specific time intervals. climate projections offer fundamental information for identifying the extent, rate, and scope of future climate change, which is essential for policy-making and planning adaptation strategies. the hydrological unit of Masjedsoleyman (Shoor river catchment area or Dasht Bozorg Basin) holds particular importance especially in the agricultural sector due to the presence of the Shoor River and groundwater resources. although various studies have been conducted in this basin, no research has yet addressed the projection of climatic variables under the extreme SSP scenarios of the IPCC sixth assessment report, which account for socio-economic activities. therefore, the objective of this study is to forecast changes in climatic variables, specifically temperature and precipitation, in the Shoor river catchment area based on the output of the CMIP6 model, utilizing SSP119, SSP126, SSP245, SSP370, and SSP585 scenarios for the future period of 2015–2050.



Materials and methods

The first part involves analyzing the trend of changes in climatic variables temperature and precipitation at the Masjedsoleyman synoptic station under current conditions. to assess the statistical significance of trends in temperature and precipitation time series, the Mann-Kendall test statistic was employed. for this purpose, annual average data of precipitation, minimum temperature, and maximum temperature from the Masjedsoleyman synoptic station were used over a 40 year statistical period (1985–2024), in order to identify the annual trend of the mentioned variables during the baseline period at the selected station. the second part of this study involves forecasting changes in climatic variables temperature and precipitation in the Shoor river catchment area using the outputs of the CMIP6 model under extreme SSP scenarios. for this purpose, general circulation Models (GCMs) from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) were selected. this project employs a new set of scenarios known as SSPs, which are combined with the representative concentration pathways (RCPs) used in the fifth IPCC assessment report. the new scenarios introduced in CMIP6 include SSP1-1.9, SSP4-3.4, and SSP3-7.0, while four other scenarios SSP1-2.6, SSP2-4.5, SSP4-6.0, and SSP5-8.5 are updated versions of RCP2.6, RCP4.5, and RCP8.5 from CMIP5.



Results and discussion

The results of examining changes in maximum temperature, minimum temperature, annual temperature, and precipitation during the baseline study period (1985–2024) indicate that at the Masjedsoleyman synoptic station, maximum temperature, minimum temperature, and annual temperature have shown an increasing trend, while precipitation has exhibited a decreasing trend. these variations in climate elements reflect the manifestation of climate change. according to the Mann-Kendall trend analysis, the maximum temperature at Masjed Soleyman station shows a rising trend, the minimum temperature also displays an upward trend, and the mean temperature follows the same increasing pattern. additionally, the Mann-Kendall test indicates a decreasing trend in precipitation over the 40-year statistical period. the combination of increasing maximum and minimum temperatures along with declining precipitation reflects a growing diurnal temperature range and reduced humidity, leading to the emergence of drier conditions in the region. the annual warming trend at the study station confirms that the region is progressing toward a warmer climate. in this study, future changes (2015–2050) in climatic variables temperature and precipitation were projected for the Shoor river catchment area based on the CanESM5 model and using the statistical downscaling model (SDSM). the accuracy and performance of the model were evaluated using statistical indicators including mean absolute error (MAE), root mean square error (RMSE), and the correlation coefficient (R). according to the results from the model performance evaluation, CanESM5 demonstrated acceptable accuracy in simulating observed values during the baseline period (1985–2014). subsequently, the CanESM5 outputs under different SSP scenarios were downscaled using the SDSM model.

Conclusion

The aim of this study is to investigate future changes (2015–2050) in climatic variables, specifically temperature and precipitation, in the Shoor river catchment area under SSP scenarios of the Sixth Assessment Report (CMIP6). according to the results obtained, the capability of the SDSM model was confirmed in this study. these findings are consistent with the results of studies by Naderi etal. (2017), Shagga etal. (2020), Wang et al. (2021), Li etal. (2021), Mesgari etal. (2022), Halim etal. (2023), Fissa etal. (2024), Azad and Ahmadi (2023), Abdolalizadeh etal. (2023), Mohammadi etal. (2024), and Maleki Marshet etal (2025). based on the conducted analyses, an increase in both maximum and minimum temperatures, as well as an increase in daily precipitation, was observed for the future period. the results of this study are in line with the findings of most researchers regarding the upward trend in maximum and minimum temperatures, as well as increased precipitation.



Keywords

Projection, climatic variables, CMIP6 Model, SSP scenarios, shoor river catchment area