Zoning Autumn Precipitation of half the west of Country: Application of the Empirical Orthogonal Functions (EOFs) in the Climatology Studies

The regionalization and study of geographical extent of precipitation pattern is important because of its expanded impact with different parts activity of agriculture. The Empirical Orthogonal Functions that known as the principal components analysis, is one of the most efficient ways to extract information from large data sets. The advantage of EOF analysis is that it provides a compact description of the spatial and temporal variability of data series in terms of orthogonal functions, or statistical "models". The efficiency of EOF analysis in the regionalization of autumn precipitation (third month: October, November, December) of half the west of Iran (44-49ْ E and 30-40ْ N) has been evaluated, that its has variety of climatologically and geographical conditions and contains 11 provinces of country. The basis of this research, eight of the first EOF, which account for 90. 74 % of total variance in the precipitation data, were kept and used for the regionalization of precipitation regions. The result of this survey show that because of component each loadings become high with part of the region that its has more homogeneous precipitation conditions, six of the first EOFs could be used as the regional time series of autumn precipitation in the part of middle zagros (Ilam, Lorestan, Kermanshah (exceptionally patagh station), hamedan provinces and mozaffarabad Ghor and Divandarreh stations from kordestan and dehe-Jalal station from Zanjan), large part of the Zanjan province and half the south of Azarbayejan region, Khuzestan province, important part of the Azarbayejan region, Gilan province (exceptionally Lahijan and Koomaleh stations) and Ardebil province respectively. Because of different of autumn precipitation between Lahijan and Koomoleh stations and the other stations of Gilan province, loadings EOF-7 and EOF-8 components have showed high for this two regions in the eastern of Gilan province. The results show that the precipitation regions have been separated desirably that they have proportiated with climatological conditions that they have been dominated on the rigions and in the other done climatological researches have been confirmed.