Statistical and Synoptic Analysis of the Rainfall-Run off in the Beheshtabad Basin

In mountainous areas with snow regimes, the precipitation is not usually affected by flood event. However, in some cases extreme rainfall causing flood events is fearsome and destructive. Despite the lack of synchronicity of extreme rainfall and discharge of floods, in some cases extreme rainfall coincides with huge floods. For this purpose, daily precipitation data from 23 meteorolgical stations of Chaharmahal and Bakhtiari Province 28.02.2001 to 21.10.2012, daily discharge datga of Beheshtabad hydrometric station in the period 21.03.1998 to 20.03.2011 and atmosphere data at 500 hfa level including variables of geopotential height, sea level pressure, zonal wind, meridional wing, omega, temperature and specific humidity, taken from NCEP/NCAR were used. The based on environmental to circulating approach they were analyzed. Synoptic analysis showed that the difference between systems with solid and liquid precipitation is in the manner of supply of their moisture. Liquid precipitation occurrence, with the establishment of anaticyclone system on the Arabian Sea is coupled. This system, due to warm and humed air mass of Arabian Sea sinks into the AMediterranean deep trough. The warm and humid air mass, the crossing of the Red Sea and the Persian Gulf are strengthened and the moisture content is added. The warm and humid air mass, in the crossing of the Red Sea and Persian Gulf strengthens and the amount of moisture is added. The rises of air causes huge instability in fron of the Mediterranean deep trough system a creates flood-causing precipitation event in the high Zagros and especially in Beheshtabad Basin.