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A comprehensive assessment of four gauging stations along the Euphrates River reach (Haditha, Al-Hindiya, Samawa, and Al-Nasiriyah) was conducted to assess the water quality deterioration spatially and temporarily for the period 2005-2021. The spotlight is on discharge rates and climate conditions, which mainly controlling water quality and availability. The mean monthly discharge rate was taken 2005–2021, in addition to the water quality parameters (TDS, pH, EC, Mg+2, Ca+2, Na+, SO4-2, Cl-, and HCO3-, BOD5, COD, FCB, and E. coli). The discharge rates showed a visible decrease downstream, causing the river salinity and all the ion concentrations to rise. The statistical package of social sciences revealed two groups of water pollution sources: The F1 reflects natural conditions produced from the dissolution of the basin rocks, with a percentage of 28.0% from the total variance; the eigenvalue is 4.4. F2 reflects the anthropogenic sources, contributing 14.5% and having an eigenvalue of 2.1. The total ionic salinity plot indicated less than 2000 mg/l at the Haditha and Al-Hindiya sites and between 3000 and 4000 mg/l at downstream sites (Samawa and Al-Nasiriyah). The transportation of dissolved loads is decreased downstream following the discharge rate as indicated by the rating curves, as follows: 781000, 542628.4, 443861, and 432950.4 tons/month for Haditha, Al-Hindiya, Samawa, and Al-Nasiriyah, respectively. Water type shows a notable downstream deterioration, from MgSO4 at Haditha and Na2SO4 at Al-Hindiya to NaCl at Samawa and Al-Nasiriyah sites.

The Tigris River discharge is constantly changing as a result of climate variations. Water flow differences will influence the water quality, the hydrochemistry and water type through time. Hence, evaluation of the relationship between the water flow,and the hydrochemistry with time is vital. The climatological data was studied for Baghdad, Kut, Ali Al Gharbi and Amara meteorological stations for 1990-2020. The data of this study covers annual flow conditions of the Tigris River, the total dissolved solids, and the main ions on monthly bases for the period 2005-2021 for the four sites: Baghdad , Kut , Ali Al Gharbi and Amara. These data were used to establish the relationships between water discharge (m3/sec) with total dissolved solids (mg/l) and main cations (Na+, Ca2+, Mg2+, and K+) and anions (Cl‾, SO42, HCO3‾). The climatological data for 1990-2020 show that the annual rainfall values of all sites decreased over time,while, the temperature and the evaporation are constantly increasing due to the climate change effects over the years. The average annual flow of the Tigris River at Baghdad and Kut sites are 535.9 and 231.8 m3/sec respectively. While for Ali Al Gharbi and Amara sites are with an average of 183.99 and 68.7 m3/sec respectively. The mean annual total dissolved solids averages are 664.7 and 759.09 mg/l for Baghdad and Kut sites respectively. While, for Ali Al Gharbi and Amara sites are with an average of 1066.1 and 1189.2 mg/l respectively. The decrease in the Tigris River discharge affects the chemistry. Calcium, magnesium, and sulfate ions in Baghdad and Kut sites are dominated. While at Ali Al Gharbi and Amara, sodium and sulfate ions are dominant. Such variation is related to the decrease in the Tigris River discharge and the effect of the dissolution of ions. Moreover, the entry of the transported dissolved load, the city’s sewage, and the agricultural lands’ water that flows into the river increase as the transportation distance increase from Baghdad to Amara.

Although the increase in water pollution, the amount of water consumption also increased in population and their activities. The effect of climatic changes are considered as the main effect on Iraqi water resources on its quality and quantity. The goal of the present research is to explain the negative effect of the decreasing of water flow and climate change on the quality of water over the years 2005 to 2010 along the Euphrates river starting from AlHindyia Barrage through Al-Samawa to Al-Nasiriya sites. Historical climatological data of rainfall and temperature for the period 1990 to 2020 and hydrological data of discharge and hydrochimecal analysis for the period 2005 to 2010 were applied in this research. Three gauging stations were chosen on the stretch of the Euphrates River, Al-Hindyia Barrage, Al-Samawa and Al-Nasiriya city. The discharge of Euphrates river is correlated with the Total Dissolved Solids, the major cations (Na+, Ca2+, Mg2+ and K+) and anions (Cl-, SO42-, HCO3-). It was found that the decrease of discharge due to shortage of water resources and climate change led to increase salinity, Total Dissolved Solids and major ions were became higher with time. The concentration of Total Dissolved Solids increased significantly to reach about 846 ppm in Al-Hindyia Barrage and this rate continue to rise in Samawa to about 2545 ppm and Nasiriya 2724 ppm. it was found that the ions Na+, So42- dominated in Al-Hindyia Barrage water while Na+ and Cl- dominated in Samawa and Nasiriya city water.