Synoptic Analysis of Floods in Bavanat Marvast River in Yazd

This study investigates the effect of synoptic analysis of Bavanat Marvast river floods in Yazd. Due to the regional aridity، there were 5 flood periods during statistical period of 9 years، i. e. 1999-2007،each one were analyzed synoptically and only the most two severe floods (6 Dec 2003 and 29 Mar 2007) were selected and analyzed. To analyze this effect، daily precipitations statistics of Marvast and nearby stations were applied to determine the intensity of instabilities and regarding the instability indices، Si، Ki، Li، TTi and Pw Shiraz station was applied. Also to analyze synoptic effects of precipitation pattern، synoptic maps of the earth surface، level of 500 hpa، omega maps، moisture and cyclonic maps at zero and 12 hours were prepared. The synoptic pattern formation and its trends in weather maps during 2 days before the flood and up to the flood ̓s day were investigated. The study results showed that there are two precipitation patterns in the region، that flood precipitation on 6 Dec. 2003 was due to the Mediterranean systems effects obtaining its heat and moisture from southern waters and caused severe precipitations. The causes of the floods on March 29th 2007 was due to the appearance of Siberian high pressure system and formation of blocking system on the southern of the Caspian sea and the center of Iran. At the same time، the west instable system clashed with this system and changed its way and penetrated in to the lower latitude so that the west system got high level of humidity whenever it transited from south seas and penetrated from southwest of the country and made sever precipitations in southwest and central region of Iran.