Evaluating the impact of climate change on Aras border river water quality using statistical methods, SWAT Model and WQISC Index

Rivers have always been considered by human societies as one of the main sources of drinking water and agriculture during human life and have been very effective in the formation of human civilizations. Aras River is a border river that is one of the most important sources of drinking water in many surrounding towns and villages. The aim of this study is to evaluate the water quality of Aras River at present and predict it for the future period under RCP release scenarios. In this study, monthly data of discharge, precipitation, TDS, SO4, EC, BOD, Do, COD, No3, and Po4 during the statistical period of 1995-2018 were analyzed using WQI water quality index. Also, changes in precipitation and temperature were predicted under RCP release scenarios. To investigate the impact of climate change on river water quality, regression relationships were established between rainfall, discharge and water quality parameters and according to the forecast for rainfall and discharge in the period 2017-2036, water quality conditions with WQI index for scenarios. RCP8.5, RCP4.5 and RCP2.6 were calculated. In addition, the effect of changes in climate parameters on the quality parameters of phosphate and nitrate was estimated using the SWAT model for the future. The results of statistical studies showed that the amount of nitrate, phosphate and COD parameters in all three scenarios will be increasing. Also, the simulation results of phosphate and nitrate parameters using SWAT model have predicted incremental conditions for all three scenarios. The results of the effect of climate change on water quality using the WQI index showed that water quality is in poor condition at baseline (WQI index is 15.69) and under the influence of climate change based on scenarios of RCP8.5, RCP4.5 and RCP2.6 WQI value 11.17, respectively; 12.23 and 12.45 and water quality will change to very bad, which requires attention to the quality of the Aras River and the prevention of pollutants.