Long-term monitoring and evaluation of drought and determining the accuracy of its indicators in western Iran

The identification and evaluation of drought events are essential to prevent and reduce their effects. This event is usually monitored and evaluated using different drought indices. This study aims to investigate the trend of rainfall, monitoring, and evaluation of drought in the western part of Iran. In this paper, five cities Orumiyeh, Sanandaj, Hamedan, Khorramabad, and Ilam, which are located in the west of Iran, were evaluated and monitored with the standardized precipitation index (SPI), percent of normal index (PNI), China-Z index (CZI), deciles index (DI), modified CZI (MCZI), Z-score index (ZSI), and rainfall anomaly index (RAI). The results showed that the annual rainfall in 11 years (2008-2018) in Sanandaj, Khorramabad, and Ilam stations was less than their average long-term annual rainfall, which was 415, 475, and 511 mm, respectively. The annual rainfall in 10 years (2009-2018) in Hamedan and Orumiyeh stations was less than their average long-term annual rainfall, which was 299 and 310 mm, respectively, during this decade of drought. The evaluation of indices in a long-term period showed that monitoring with the SPI in semi-humid and semi-arid climates was more accurate than the other indices. The CZI was ranked second in importance in these climates due to the high correlation of 93%.