Analyzing Spatial Relations of Extreme Precipitations of Western Iran

Extreme precipitations at each point are those irregular precipitations which are situated in the trail and away from the focus point of the precipitation frequency distribution of that point. Recently, the thresholds and upward trails of precipitation frequency distribution have been greatly regarded. In this regard, and proportionate to the geographical properties of each zone, various and numerous thresholds have been introduced and applied for this precipitation property. One of the frequently-used indices of daily precipitation is based on generalized distribution of extreme values. In this research, extreme precipitations’ threshold of western Iran have been determined using extreme values generalized distribution statistical methods, extreme precipitations of the region have been recognized, and their spatial distribution has been analyzed. To this end, network data resulted from daily interpolation of 69 synoptic stations and climatology for 1961-2010 statistical periods was used. Then by using generalized distribution method of extreme values, the daily precipitations of 22mm and more were selected as the Extreme precipitations. In order to recognize the distribution pattern and spatial relations of western Iran extreme precipitations (Hamadan, Kordestan, Kermanshah, Lorestan, and Ilam provinces), Global Moran’s I statistic, Local Moran’s I statistic, and Getis- Ord G* statistic were used. The spatial pattern of western Iran precipitations is a cluster pattern, the significance of which was confirmed at 99 percent confidence.Frequency clusters and average clusters of extreme precipitations are compatible with each other in some regions including Hamadan and Kordestan provinces, but there were no relationship between them in some other regions. The most frequency and average of precipitation frequency was happened in Hamadan and Kordestan provinces. Based on the both indices of Local Moran and hot spots of the region's heights of the study area has had a recognized role in the extreme precipitation patterns with the high clusters. The result of the study showed that the frequency and average of extreme precipitation of western Iran is influenced by unevenness, the deployment of unevenness, as well as synoptic systems.