Investigating the relationship between 500 HP level changes and flood in Urmia Lake Basin

Many of environmental conditions are explainable, either directly or indirectly with regard to topographical changes in pressure levels of high atmosphere. Thus, studying this subject is great importance. In this article, after determining the threshold of flood in catchment, Altitudinal data of 500 HP level for 44 storms generating floods during (1370_1384) were processed using the factor analysis method. Ultimately, based on correlation matrix (variance-covariance), main focuses of topographical changes of 500 HP level, affecting extensive and catastrophic floods were recognized and analyzed. Research results showed that, during flood occurrence, the following five focuses have the most Anomaly of 500 HP altitudinal level: 1) The area between the Red sea and south west of Iran 2) The area between the centre of Mediterranean sea and the black sea 3) The northern part of Caspian Sea 4) East of Iran 5) Northern part of Europe. Such changes in 500 HP level lead to enforcement and deepening the axis of troughs and ridges, and have produced synoptical patterns that cause floods. In the meantime the changes in 500 HP level in the first and two focuses have the most effect in creating floods of aforesaid catchments.