Iran and Iraq face a water shortage crisis especially in the recent decade. Hence, the regions with high potential water resources are highly important to these countries. Precipitation sampling for 18O and 2H analyses was conducted in 10 stations in the west of Iran and 2 stations in the east of Iraq during this study. Studying precipitation and its moisture sources using the backward trajectories of the HYSPLIT model, developing seasonal meteoric water lines (MWLs), and simulating the spatial variations of stable isotopes in precipitation using stepwise regression yielded valuable results regarding the hydrometeorology of the study region. The precipitation moisture sources in the study region were determined using the backward trajectories of the HYSPLIT model. These backward trajectories demonstrated the domination of various moisture sources including the Mediterranean Sea, the Black Sea, the Red Sea, and also the Persian Gulf in different seasons as reflected in the seasonal MWLs. In addition to moisture sources, the effects of meteorological parameters (temperature and precipitation amount) on the stable isotope content of precipitation also showed a notable correlation (with R2 = 0.58 and 0.46, respectively). Surface water resources were also plotted on the developed seasonal MWLs, while some samples deviated from seasonal MWLs due to the evaporation effect.

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