A new model for vulnerability assessment of drought in Iran using Percent of Normal Precipitation Index (PNPI)

Document Type: Regular Paper


Department of Natural Resources and Environment, College of Agriculture, Shiraz University, Iran


The Percent of Normal Precipitation Index (PNPI) 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 PNPI index. In this paper, according to the data of 40 stations in Iran, during 1967-2009, the pattern of drought hazard is evaluated. Influenced zone of each station was specified by Thiessen method. An attempt was made to create 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. Both the vulnerability indicator map and also final hazard map are classified into 5 hazard classes of drought: None, 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 the mean of the main indicators, deploying the new model. The final vulnerability map shows that severe hazard areas (58% of the country) which are observed more in the northwestern, southeastern and central parts of the country are much more widespread than areas under other hazard classes.