Document Type : Research Article
Department of Range and Watershed Management, Faculty of Agricultural and Natural Resources, University of Mohaghegh Ardabili, Ardabil, Iran
Department of Watershed Management Engineering, Faculty of Natural Resources, Tarbiat Modares University, Noor, Iran
Young Researchers and Elite Club, Bojnourd Branch, Islamic Azad University, Bojnourd, Iran
The wet and dry spells can be defined as a number of consecutive months with rain amount greater or less than the truncation level, respectively.Analysis of the wet and dry spell properties of monthly rainfall series at 40 meteorology stations in the Golestan Province is carried out for an extended period of 34 years (1974–2007). The results proved that the patterns of wet and dry spell durations can be determined using power law technique. Wet and dry spell duration characteristics, as well as the frequency of dry spells for the length of (1-9 months) are discussed. The longest dry spells are identified in North-east of the Golestan province in Tamar and Minudasht stations with 5 and 6 times occurrence respectively. Whereas longest wet spell with the 9 months length is shown over the central part of the study area. It has been observed that the longest durations of dry periods occur in the stations that located in the Northern part of the Golestan Province. The interpretations of double logarithmic plots of (frequency versus length period) can be used to compare the occurrence patterns of wet and dry spells in the stations over different precipitation regimes. Further applications of power law method are suggested to obtain a better understanding for the interpretation of wet and dry spells regions with different climatic conditions.