Climate change and drought can lead to a decline in surface water quality within catchment areas. understanding the complex impacts of climate change and drought assists water resource managers in monitoring the changes that have occurred in a catchment area and in making correct decisions when developing a catchment area management plan. the aim of this research is to assess the surface water quality of the shoor river catchment area under conditions of climate change and drought. in this research, observational data (baseline) including minimum temperature, maximum temperature, and daily precipitation from the masjedsoleyman synoptic station and NCEP data were used to select predictors or variables affecting temperature and precipitation forecasting and data from the CanESM5 model under scenarios SSP119, SSP126, SSP245, SSP370, and SSP585 were utilized for projecting climatic variables during the observational period (baseline) of 1985-2014 and the prediction period (future) of 2015-2050. using the Standardized Precipitation Index (SPI), the meteorological drought status of the Shoor river catchment areas was calculated for the statistical period of 1985-2024 with the help of DIP software and the Excel environment. in this research, recorded data of water quality variables from the dashtbozorg hydrometry station, including measured chemical parameters: TDS، EC، PH، Cl-، SO42-، CO32-، HCO3-، Mg2+، Na+، Ca2+، K+، SAR and the discharge on an annual scale during the 40 year statistical period (1983–2023) using statistical methods; the non-parametric Mann–Kendall (MK) analysis, Sen’s slope estimator (Qmed), Pearson correlation test, the Kolmogorov–Smirnov method, and the Kaiser–Meyer–Olkin (KMO) method in SPSS27 software were investigated. finally, using factor analysis and analysis of variance, the effect of climate change and drought conditions on surface water quality parameters was investigated. the results show that among the studied parameters; total Dissolved Solids (TDS) and Electrical Conductivity (EC) have the highest correlation with the average temperature with values of 0.248 and 0.175. total Dissolved Solids (TDS) has a negative correlation of -0.191 with drought, and Electrical Conductivity (EC) has a positive correlation of 0.138 with drought. total Dissolved Solids (TDS), Electrical Conductivity (EC), and Acidity (PH) have negative correlations of -0.153, -0.014, and -0.198 with precipitation, and Sodium Adsorption Ratio (SAR) has a positive correlation of 0.018 with precipitation. Electrical Conductivity (EC) has the highest correlation with Sodium Adsorption Ratio (SAR) and Total Dissolved Solids (TDS) with values of 0.832 and 0.497, and has not shown a high correlation with climatic parameters. also Acidity (PH) has a negative correlation with drought of -0.293, and Sodium Adsorption Ratio (SAR) has a negative correlation of -0.012 with drought. based on the changes and the role of precipitation and temperature in the variations of surface water quality parameters, the impact of climate change and drought on these parameters can be confirmed.



Extended Abstract

Introduction

Climate change and drought can lead to a decline in surface water quality within catchment areas. understanding the complex impacts of climate change and drought assists water resource managers in monitoring the changes that have occurred in a catchment area and in making correct decisions when developing a catchment area management plan. the aim of this research is to assess the surface water quality of the shoor river catchment area under conditions of climate change and drought.



Methodology

In this research, observational data (baseline) including minimum temperature, maximum temperature, and daily precipitation from the masjedsoleyman synoptic station and NCEP data were used to select predictors or variables affecting temperature and precipitation forecasting and data from the CanESM5 model under scenarios SSP119, SSP126, SSP245, SSP370, and SSP585 were utilized for projecting climatic variables during the observational period (baseline) of 1985-2014 and the prediction period (future) of 2015-2050. using the Standardized Precipitation Index (SPI), the meteorological drought status of the Shoor river catchment areas was calculated for the statistical period of 1985-2024 with the help of DIP software and the Excel environment. in this research, recorded data of water quality variables from the dashtbozorg hydrometry station, including measured chemical parameters: TDS, EC, PH, Cl-, SO42-, CO32-, HCO3-, Mg2+, Na+, Ca2+, K+, SAR and the discharge on an annual scale during the 40 year statistical period (1983–2023) using statistical methods; the non-parametric Mann–Kendall (MK) analysis, Sen’s slope estimator (Qmed), Pearson correlation test, the Kolmogorov–Smirnov method, and the Kaiser–Meyer–Olkin (KMO) method in SPSS27 software were investigated. finally, using factor analysis and analysis of variance, the effect of climate change and drought conditions on surface water quality parameters was investigated.





Results and discussion

The results show that among the studied parameters; total Dissolved Solids (TDS) and Electrical Conductivity (EC) have the highest correlation with the average temperature with values of 0.248 and 0.175. total Dissolved Solids (TDS) has a negative correlation of -0.191 with drought, and Electrical Conductivity (EC) has a positive correlation of 0.138 with drought. total Dissolved Solids (TDS), Electrical Conductivity (EC), and Acidity (PH) have negative correlations of -0.153, -0.014, and -0.198 with precipitation, and Sodium Adsorption Ratio (SAR) has a positive correlation of 0.018 with precipitation. Electrical Conductivity (EC) has the highest correlation with Sodium Adsorption Ratio (SAR) and Total Dissolved Solids (TDS) with values of 0.832 and 0.497, and has not shown a high correlation with climatic parameters. also Acidity (PH) has a negative correlation with drought of -0.293, and Sodium Adsorption Ratio (SAR) has a negative correlation of -0.012 with drought.



Conclusion

Based on the changes and the role of precipitation and temperature in the variations of surface water quality parameters, the impact of climate change and drought on these parameters can be confirmed.