Characteristics of Drought in Three Recent Decades in North of Iran, Guilan Province

3 Abstract: The drought monitoring in Guilan, particularly its intensity, duration, frequency and the extend area have been analyzed for the period '1966 - 2002' by SPI method. The results showed that droughts occurred periodically within the region and relatively regular cycles and frequency of the occurrence of drought was different at wet and dry stations. The highest frequency for each station is generally moderate and severe type in relation to wet stations. The correlation of SPI values in 19 stations distinguished a synchrony of the occurrence of drought in adjacent stations and its rate reduced with increasing distance. Finally, spatial-temporal pattern of drought after the monitoring indicated an occurrence of continuous and discontinuous droughts in study area which caused, provided the critical conditions for natural and human resources.