The occurrence of climatic hazards such as destructive floods in southwestern Iran is one of the inherent characteristics of the climate in this region. Two rainfall systems between 23 March to 2 April 2019 caused extensive rainfall in most provinces of the country and devastating floods in Lorestan and Khuzestan provinces, causing extensive flooding of cities and villages and imposing extensive damage to infrastructure. It had economic and social consequences. In this study, it is attempted to study the large-scale synoptic patterns and the mechanism of divergence of moisture flux from moisture sources around Iran in heavy rainfall systems. Daily data of more than 300 stations were used for the period 1981 to 2010 for calculating the wetter years from October to May. Investigation of atmospheric patterns of moisture flux divergence from moisture sources around Iran to the study area in the wetter months was done for three time periods and four different layers of the troposphere. The results showed that heavy rainfall leads to flooding in southwestern Iran under the influence of a dominant pattern and the western parts of the Indian Ocean have an important role in moisture flux divergence in all of the tropospheric layers. Indian Ocean and the Oman Sea accounted for about 50 percent, the Red Sea and the Persian Gulf each about 21 percent and the Mediterranean share of 8 percent in moisture flux divergence. Therefore, the patterns of atmospheric systems in the northern Indian Ocean and the location of the Mediterranean trough play an important role in predicting heavy rainfall in the region.
Therefore, the patterns of atmospheric systems in the northern Indian Ocean and the location of the Mediterranean trough play an important role in predicting heavy rainfall in the region.
Key words: Flood, moisture flux, high pressure Saudi Arabia, southwestern Iran.