Climatology of Precipitation in North West of Iran

Climatology of precipitation can be defined as the dominant behavior of precipitation in any place. One of the methods for analyzing the precipitation climatology is the recognition of cyclic behavior of precipitation. This important issue is possible through analyzing and studying different accordants of precipitation. In fact conformes show different latent aspects in a time series. The importance of accordants is defined based on the diffraction of frequency features in a time series. In this study, it is tried to detect the latent aspects of precipitation in west part of Iran (west Azerbaijan, East Azerbaijan, Ardebil and Zanjan provinces). In this regard, 260 synoptic, climatology and udometer stations were used during statistical period of 1996-2005. In order to remove statistical deficiencies and compensate for length difference of statistical period, monthly precipitation maps were produced and arithmetic operations were made on the cells of these maps to obtain features of accordants. Annual precipitation of the north west part of Iran will increase from north east to south east. In spite of what expected, maximum rainfall will not occur in the heights of this area of country. In addition, spatial variations of precipitation are too great. Based on the used methods, it was cleared that two local synoptic systems justify up to more than 90 percent of north west precipitation. Maximum amount of precipitation due to synoptic systems occurs in northeast (low rainfall). therefore the share of precipitation resulting from local systems (convection precipitation, mountainous precipitation, local fronts and.) is more in this part. Mean while, proportionate to the increase of annual precipitation, the share of synoptic systems will also increase. South west parts receive greater maximum precipitation than synoptic systems. The time of maximum precipitation occurrence, due to synoptic systems in the northern, is early December but in Southern half is late December and early January.