Review of synoptic structure for 24-hours heavy rains in Khuzestan province (during 1996-2000)

Khuzestan province which is located in southwest of Iran usually has low rainfall although sometimes heavy rain events records in this area. Recognition of Mechanism of forming, trajectory and humidity content of weather systems, that are associated with rain event, can have role important in distinction early flood, control flood, raceway, and watershed and reduce flood damage. First, the dates of heavy rains exceeded to 70 mm, occurring in Khuzestan province, were extracted during 1960 to 2000. Then using NCEP\NCAR reanalysis data, synoptic structure including mean sea level and geopotential height at 500 hPa levels were examined in all rain events, afterward, the composite structure was obtained by averaging in similar cases and finally synoptic structure composite was analyzed. Over all, the result showed five different synoptic patterns that can produce heavy rains in south western parts of Iran. They are called Sudan, special Sudan that extended to eastern Mediterranean, Sudan- Mediterranean low, northern Africa, Mediterranean low pressure, respectively. The results of this study also showed that in addition to Sudan lows, Mediterranean systems can produce heavy rains in south western part of Iran although their frequencies are less than Sudan lows. Also some weather systems that formed in west northern of Africa, after passing from north eastern Africa and Red sea close to Saudi Arabia and Iran, have important role to produce heavy rains in this region. Because of importance of forming area of weather systems and their trajectories in heavy rain events, it should pay more attention in determining the weather systems types that produce heavy rains in Khuzestan province.