Comparative Evaluation of Four Meteorological Drought Indices using the Cluster Analysis (Case study: Sistan and Baluchestan)

The mean annual precipitation (MAP) is the most important criterion used in drought classification. Different indices have been developed based on the MAP for drought classification، of which four most commonly used are: the percentage indices of normal (PN)، the standardized precipitation index (SPI)، deciles (DPI) and the rainfall anomaly index (RAI). Each of these indices is classified into classes for drought description. Each class is represented as a state of severe drought. This study compares these indices benefiting from the rainfall data collected during 30 years (1980-2010) at seven stations in the Province of Sistan andBaluchestan. After calculating the indices during the desired time scale، the results were classified and evaluated based on sequence similarity factors of dry، normal and wet years، and by using the cluster analysis and developing statistical correlation between them. The analysis indicated that the PN index and RAI were statistically similar and lead to identical results in the dry and hot climate of Sistan and Baluchestan. It was further revealed that، the paired PN-RAI، PN-SPI and SPI-RAI were highly correlated at most of the stations. Moreover، the PN index and the RAI were placed in one class in the cluster analysis. Calculations indicated that the results of PN and RAI criteria were close to each other in terms of describing drought. Therefore، these indices are recommended for determining the drought severity in the province of Sistan and Baluchestan. Despite the widespread use of the SPI، this index is not suitable for determining the severity of drought in this province.