A New Methodology for Drought Vulnerability Assessment Using SPI (Standardized Precipitation Index)

The Standardized Precipitation Index (SPI) is a widely used drought index to provide good estimations about the intensity, magnitude and spatial extent of droughts. The objective of this study was analyzing spatial pattern of drought by SPI index. In this paper, according to the data of 30 stations in Fars Province located in the southern Iran, during 1972-2006, the pattern of drought hazard are evaluated. Influenced zone of each station was specified by Thiessen method. It was attempted to make a new model of drought hazard using GIS. Three criteria for drought were studied and considered to define areas under vulnerability. Drought hazard criteria used in the present model include: maximum severity of drought in the period, trend of drought, and the maximum number of sequential arid years. Each of the vulnerability indicator map and also final hazard map are classified into 4 hazard classes of drought: slight, moderate, severe and very severe. The final drought vulnerability map was prepared by overlaying three criteria maps in the GIS and the final hazard classes were defined on the basis of hazard scores arrived at by using the geometric mean of the main indicators, deploying the new model. The final vulnerability map shows that moderate hazard areas (74% of the region) are much widespread than areas under severe hazard (26% of the region) which are observed in the northwest and eastern parts of the region.