Case Study of Flood Rainfall in March 2019

In March 2019, passing frequently baroclinic waves over many parts of the country caused severe rainfall, resulting in flooding of rivers and extensive waterlogging in some of these areas. The incidence of these heavy and extensive rainfalls has been rare during the statistical period. In this study, three atmospheric systems resulted in severe rainfall in Golestan, Lorestan, Fars and Khuzestan provinces, which caused a great deal of damage to some part of these provinces, from the statistical an synoptically approaches has been investigated. The statistical results showed that the highest daily precipitation in March 2019 at Gorgan and Poldokhtar stations were extreme precipitation with a return period of 500 and 29 years respectively, but at Shiraz Station return period is less than 2 years. The climatological study showed that the abnormality in mean sea level pressure and geopotential height at level of 500 hPa, in March 2019 were negative over Iran and positive over Europe. This indicates an increase in cyclone formation in the southwest of the Mediterranean Sea and increase in the frequency of passage of these systems from Iran. The results of the synoptic survey showed that the high ascending motions with adequate moisture feed have created favorable conditions for occurrence of moderate and severe convective precipitation in Golestan and Lorestan provinces.