Evaluation of wet and dry periods in north west of Iran

Abstract : In this paper evaluation of wet and dry period of northwestern region of Iran (Aras and Urmia basins) is carried out, using graphical representation and calculation based on mathematical modeling. Monthly precipitation records of twenty stations for a period of 33 years, from 1970 to 2004 were chosen and fluctuations of each period with respect to their numbers were plotted on a semi -logarithmic scale and the regression equations were obtained. Accordingly since the longest wet and dry period happens only once in each period, it is possible to estimate the durations of wet and dry period for each station using the semi-logarithmic graphic representation mentioned above.