Using several drought indices in Water resources management in drought condition (Case Study of Shahid Abbaspour Dam Station)

Drought is one of the natural disasters that cause great damage to human life and natural ecosystems and is different from other natural disasters. The main differences in the gradual impact of drought over a relatively long period are the impossibility of determining the exact time of onset and end and the geographical extent of its impact. On the other hand, the lack of an accurate and acceptable global definition of drought has added to the complexity and confusion of this phenomenon. And the severity of droughts was determined and described based on drought indices ZSI, PNPI, SPI. These indicators are consistent with each other so that based on the above indicators. the results show that in Shahid Abbaspour Dam in the wet years (2007-2008) the most severe drought occurred in the statistical period. SPI index of drought periods Shows more, so it is a more sensitive index than ZSI and PNPI and has a higher sensitivity and more complete classification in the study of dry periods.