Spatial –Temporal Analysis of Drought in Iran Using SPI During a Long - Term Period

Abstract

This investigation represents temporal and spatial analysis of drought events over Iran for a 42 - year period (1963 - 2005). At first, the severity of drought occurrences over Iran has been identified using SPI (Standardized Precipitation Index) at various time scales (i.e., 3, 9, and 12 - month) for 50 synoptic stations. Then the spatial distribution of annual and seasonal drought severity using SPI - 12 months and SPI - 3 months respectively have been derived. Seasonal drought has been determined for spring, autumn, and winter using SPI - 3 months for May, Nov and Feb respectively. Maps of annual and seasonal drought showed occurrence of drought in most parts of Iran mostly in following years, 1985, 1990, 1998, 1999, 2000, and 2001. Based on the frequency of each drought severity category at different time scales (SPI - 3, 9, and 12 months), time series of number of stations experienced drought were derived. They showed that mild drought has been occurred continuously in about 85% - 95% of stations from 1998 through 2001 using SPI - 9 months and SPI - 12 months. But SPI - 3 months showed mostly 99% of stations were affected by drought continuously from 1998 through 2002. Finally, spatial distribution of each drought severity categories for different time - scales were derived.