Investigating the Drought Periods Using Precipitation-based Indices in Some Regions in Central and Western Iran

In this study, to evaluate and comparing of drought and wet occurrences, Annual rainfall data related to a 60-year period were used for Kermanshah, Kordestan, Kerman and Yazd provinces. Among the different drought indices, the precipitation-based indices such as, Standardized Precipitation Index (SPI), Percent of Normal Precipitation Index (PNPI), Z-Score Index (ZSI) and Nitzche model were used. The results showed that the classification the dry periods indicated all provinces in the recent decade have experienced a period of prolonged drought. The number of drought occurrences of Yazd, Kermanshah, Kerman and Kordestan provinces had the highest frequency, respectively. ZSI index showed more drought periods. This index is more sensitive and more complete classification than two SPI and PNPI indices in investigation of dry periods and its similarity is very close to SPI index. But The Standardized Precipitation Index (SPI) because of having more capabilities such as more detailed classes in drought phenomenon, higher accurate in dry periods and more sensitive to precipitation variation, was recognized the best model because of avowing statistical characterization of precipitation (Intensity and Abundance) and separating droughts in four provinces.