Investigation of latent droughts hyper-arid climate of Iran(Case study: center, south and east of Iran)

Drought is one of the climatic hazards that is of special importance. One of the problems of drought studies is the over-normal rainfall along with a relatively long period of drought. This divert SPI index; To the extent that sometimes, despite the occurrence of drought, the index incorrectly shows that period as normal or even wet and leads to incorrect decisions in drought management plans. In this study, SPI drought index in 8 provinces with 27 synoptic stations located in the center, south and east of Iran with De Martonne hyper-arid climate in a period of 34 years (1985-2019) for a period of twelve months was calculated and analyzed. In this study, for the first time, the EP-SPI hybrid index is presented in which effective precipitation data was used as program input. Thus, the effect of older rainfall is reduced and the index provides a better estimate of drought. The results of statistical analysis of EP-SPI versus SPI values show a significant correlation at the level of 5%. 83% of the events with a difference of more than one in October to March and the highest difference between the two methods is equivalent to four levels of drought index displacement from wet Severe to moderate drought. In this study, it was found that 9.3% of the events of the 12-month drought remained hidden from the SPI index. Therefore, it can be said that the efficiency of EP-SPI method for detecting latent droughts in a period of twelve months is confirmed.