Characteristics of stable Isotopes of the heavy rainfall event of April 2019 in Southwest Iran comparing with LMWL of other regions of country and neighboring countries

The heavy rainfall event of April 2019 with 230 mm, i.e. 46% of the mean of annual rainfall of southwest Iran, over 4 days caused the overflow of Dez and Karkheh large dams and huge financial losses. In order to determine the characteristics of stable isotopes of 2H and 18O of this extreme event, 43 samples of rain water were collected in the area about 41000 (Km2) in southwestern Iran with altitude ranging between zero to 2814 m above sea level (a.s.l). The variations of the isotopic values of δ18O and δ2H were 4.71 to -4.76 and -26.06 to 29.2, respectively. The local meteoric water lines were calculated during the flood event and compared with the corresponding global, Mediterranean and other parts of Iran values as well as neighboring countries. According to the equation of LMWL (δ2H = 6.5996 δ18O + 7.561) and deuterium excess (between -9.26 to 15.55 with average value of 7.85), it is concluded that the source of precipitation in the study period was the integrated effect of the of Mediterranean and Red Sea air masses. Deuterium excess increased from the south and southwest of the study area to higher altitudes (located in north and northeast), indicating depletion of the isotopic composition toward the high altitudes.