Synoptic Patterns of the Most Severe Drought Over Uremia Lake Basin

Drought is one of the natural disasters that causes a lot of damages each year. This phenomenon is a result of severe and repeated spatial-temporal anomalies in atmosphere circulation patterns. Thus, studying and identifying the synoptic patterns of this phenomenon is inevitably necessary. In this study, first yearly rainfalls in selected stations of the Uremia Lake Basin were temporally standardized. Before defining the spatial-temporal treatment of rainfall, 1999 was selected as the most severe drought in the area. Then, level 500 HP height data located in a scope of 0 to 70˚ northern latitude and 10 to 70˚ eastern longitude was formulated as an S-mode matrix for non-raining days. Consequently, in order to identify and classify the synoptic patterns of drought, the statistical method of Component Analysis and Clustering were used. Finally, the composite map of each cluster was prepared and analyzed synoptically. The findings show that at the time of the most severe drought over the catchments area four synoptic patterns prevail; so that after the humidity period in the middle levels of the atmosphere, a quite deep ridge will be settled in the area and consequently a quite powerful high pressure tripped will be prevailed over the land area. These conditions result in stable weather and no rainfall and finally causing the most severe drought in the area.