The Relationship of Drought Intensity, Duration and Frequency in the Southern Coast of Caspian Sea

2 Abstract: Present study investigated the drought in the southern coast of Caspian Sea, Iran. The rainfall data were obtained from five meteorological stations (Anazali, Rasht, Ramsar, Babolsar and Gorgan) for the past 48 years (1956-2003) in order to study of droughts. In the first, the drought coefficients are calculated on the basis of SPI and then characteristics of drought (intensity, duration and frequency) were analyzed. The results suggested that the high frequency of wet is one of the main distinguishing elements of the area. This included about 62-83 percent of droughts, which occurred between 1-3 months. Therefore, the long-term drought has had the least frequency. In addition, the drought coefficient had high correlation in the western stations rather than eastern stations that were revealed droughts no occur concurrently. The relationships between duration and intensity of drought indicated that increasing of intensity and duration is relevant the decrease of frequency. Meanwhile, it was seen in the sub-periods, too.