Stable Drought and Its Trait Analysis in Guilan Province

Drought is a repetitive phenomenon in different continents and its effects are not limited only to dry and semidry areas, but they could also be seen in areas with high rates of precipitation and in any season of year. One of the most important stages in monitoring the drought is to determine indices in order to analyze its intensity, continuity and frequency. The data related to the overall monthly precipitation collected from synoptic stations of the area during the statistical period of 1976-2005 which have been used for monitoring drought in Guilan and analyzing its characteristics. In the present study, continuity, intensity and frequency of drought have been extracted by using two indices, the standard distribution, and deciles and by the help of time series from standardized precipitation index.  The results of this study indicated that the two analyzed methods give the same results and drought is not an infrequent phenomenon in the rainy part of northern Iran, but it is a repetitive and reversible phenomenon. The surveys indicated that in 1991 and 1995, an intense drought has happened in the province.