Investigation and Comparison of Wet and Dry Periods in The Several Climatic Areas of Iran

In order to analysis short-term wet and dry periods and predict the occurrence probability of wet periods in 1 to days in the several climatic areas of Iran¡ the rainy days with 0.1 mm and more for 30 years (1976-2005) at 9 selective station were investigated by applying the tow-state¡ First-order Marcov chain. The important features in relation to short wet and dry periods as well as conditional and climatic probabilities¡ day¡ s abundant¡ the length of wet and dry periods and eventually the occurrence probability of 1 to 6 day periods were recognized. In all of these stations under study¡ the most abundant percentage of wet days occurs in winter and decrease in spring and autumn and the amount of reduction intensifies in the stations in the south¡ south eastern and central area of Iran. The maximum transition probability of two successive wet day (P11) occurred in Rasht¡ Khorramabad and Tabriz and the minimum P11occures in Zabol¡ Yazd and Bandarabbas. The more we move from the north and west to the south eastern of Iran¡ the more the climatic probability of wet periods (π1)¡ the length of wet period (E1) and the frequency of rainfall 1 to 6 days decreases and in the other hand duration of the weather cycle (Ec) increases. In all of station¡ the occurrence probability of one-wet-day is more than others and the more duration of wet period’s increases¡ the occurrence probability of them decreases.