Determination of Isotopic Composition of Precipitation to Generate Local Meteoric Water Line in Iraq

The stable isotopic compositions of hydrogen (δ 2 H) and oxygen (δ 18 O) in precipitation serve as valuable indicators for perceptive the characteristics of precipitation, the mechanisms of groundwater replenishment, and for conducting climatological investigation. Environment isotope monitoring in Iraq, was conducted, with the assistance of the International Atomic Energy Agency IAEA and the World Meteorological Organization WMO as a part of the worldwide activity entitled Global Network of Isotopes in Precipitation GNIP. Precipitation samples were collected from main station sites in Iraq during the period (2023-2024), represented 154 samples .Rain samples were collected with the support of the Iraqi Meteorological Organization and Seismology, under the supervision of authorities from meteorological stations across various governorates in Iraq. The isotopic measurements of (δ 2 H) and (δ 18 O) were obtained from WISER website. The linear regression analysis was employed to regulate the relationship between δ 18 O and δ 2 H in rainfall. This work aimed to generate Local Meteoric Water Lines LMWL in three main regions across Iraq (Western, Northern, and Central/Southern) and compare them with the LMWLs for the neighboring countries. The results showed that Northern region, NMWL (δ2H= 7.9171δ 18 O + 15.011) exhibit depletion in precipitation isotope δ 18 O and δ 2 H values reflecting moisture contributions from the Mediterranean and black sea. While, western region with, WMWL (δ 2 H =5.7526 δ 18 O + 7.3653); appear to be dominated by evaporation enrichment of δ 18 O and δ 2 H. And central and Southern region, CSMWL (δ 2 H = 6.6102 δ 18 O + 10.412) experience relatively enriched δ 18 O and δ 2 H values, likely due to evaporation effects and moisture contributions from the Arabian Gulf. The fluctuation in δ 1 ⁸O throughout longitudinal transect related to the air mass trajectories and moisture origin, effecting isotopic composition of precipitation.Furthermore, a depletion in isotope levels was seen in the northern region based on the spatial distribution of precipitation isotopes. Conversely, the western region displayed relatively enriched isotope levels. Additionally, there is greater isotope value enrichment in the central and southern regions.These findings contribute to to identify locations with high and low precipitation, support in water project management, agricultural improvement, and drought and flood prediction.