Iran is a semi-arid and arid country which always faces a water shortage crisis. Thus, the water resources in Iran should be studied by accurate methods such as stable isotope techniques. In precipitation sampling stations across Iran, the δ18O (ranges from −16.3 to −0.3 ‰, −4.9 ‰ average), δ2H (−114 to –13 ‰, −24.2 ‰ average) and d-excess (−2.1 to –22.7, 16.5 ‰ average) values are higher compared to δ18O (ranges from −10.9 to −3.1 ‰, −6.7 ‰ average), δ2H (−71 to −6 ‰, −37.4 ‰ average) and d-excess (1.0 to –21.6 ‰, 14.9 ‰ average) values in groundwater stations. Stable isotope distribution maps in precipitation and groundwater were also developed for Iran. The stepwise technique was used to study the role of parameters influencing stable isotopes in Iran precipitation. Results show the dominant role of temperature, elevation and latitude as well as ‘cP and MedT’ air masses mixture on stable isotope values in precipitation. Furthermore, the contribution percentage of each air mass which influences Iran in groundwater resources recharge was studied using ‘Simmr’ package in R programming language. Finally, the accuracy of the developed stable isotope distribution maps was validated.

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