A comparative study of precipitation-based drought indices with the aim of selecting the best index for drought monitoring in Iran

Drought is a natural disaster that occurs frequently or intermittently and affects all economic, social, and environmental aspects of a society. The present study is an attempt to compare different drought indices and select the best drought index for drought monitoring in Iran. To this end, seven drought indices including SPI, PN, ZSI, DI, CZI, EDI, and MCZI were used for 1-, 3-, 6-, 12-, and 24-month timescales. The monthly precipitation data of 41 synoptic stations in Iran over a period of 28 years (1985–2013) were used in order to achieve the research objectives. After the required databases were obtained, the effective drought index (EDI) was used as a basic indicator and as the basis of calculations in order to choose the best index for drought monitoring. The results showed that the EDI index indicates the general drought classes better than other indices. Of the indices used in the study, three indices namely ZSI, SPI, and CZI showed the highest consistency in their behavior. In addition, the 6-, 12-, and 24-month timescales showed very similar drought results in the abovementioned indices. Moreover, the behavior of DI and PN indices proved to be inconsistent with the behavior of other indices, and these indices proved to be unsuitable for drought monitoring in Iran. The MCZI index, as compared to the EDI index, showed no acceptable performance in drought monitoring. Finally, SPI and EDI indices were detected as the first and second best indices for drought monitoring in Iran.