A Study of Floods Based on the position Synoptic Systems in Yazd Province

One of the natural phenomena which results to harmful damages all over the world every year, is the occurrence of severe flood. This phenomenon also occur in Iran, especially in dry and desert regions. In spite of placing subtropical high pressure centers during some months of year on most parts of country followed by lack of atmospheric precipitations for consecutive months, considerable amount of rainfall can be occur in other months and result to harmful and destructive flood.Yazd province is subject to flood because of its climatic and geographical situation which is located in dry and desert region of central Iran, and incur great damages in this regard periodically. Therefore, understanding the process, its occurrence and identifying synoptic patterns resulting to flood in this province can be useful in forcasting and reducing the harmful effects of this phenomenon. This research has been conducted using daily precipitation data in Yazd stations, surface and upper levels synoptic maps, also upper atmospheric data in Yazd, Kerman, Shiraz, Esfahan and Bandar Abbas stations during the intended statistical period for 10 selected flood samples.The results of this study show that the presence of cylones for several consecutive days may result in the occurrence of flood to this province. Red sea and Sudan low pressure systems which enter Yazd province through the south western part of the country, if allowed to take sufficient heat and moisture from southern waters, result to flood. Mediterranean- Sudan compound systems which obtain moisture again after passing Zagros possesses severe instability, create flood in Yazd province. The intensity of floods depends on the arrangement of synoptic patterns of atmospheric systems.