The role of the Red Sea in moisture feeding of flood events of Iran with emphasis on atmospheric river concept

Southwest Asia is located in the descending branch of the Hadley cell with a dry climate. As one of the countries located in this area, Iran receives 220 mm annual rainfall, equal to one-third of the global average. However, various severe and short-term torrential rainfalls, which lead to a flood event in some areas, could be observed in the precipitation season each year. Therefore, mechanisms of transferring huge moist air from the nearby water basin to the country at the time of the flood and its interaction with the complicated topography of Iran is a fundamental question that so far was less investigated. In the present study, the moisture routing is examined for two flooding events in the south and west of Iran using the Atmospheric Rivers (AR) algorithm. Furthermore, the divergence of the moisture flux was applied to determine the source and sink of humidity. The results showed that an AR event which has received moisture from the Red and Arabian Seas has accompanied by flood event in the west of Iran. But the main humidity source of the second one has been the Persian Gulf which did not have AR characteristics. The low-level flow in the two cases was the main factor to transport humidity from the nearby water basin to the inland of Iran. While the convergence of moisture due to upsloping motion over the Zagros Mountain was the main cause of heavy rainfall and flood event. The moisture path of the two cases originated from the divergence zone associated with the cold front of the low pressure then intensified and fed on the way by other water basins.