عنوان مقاله [English]
Drought is one of the most important climate phenomena which occur in all climate conditions and regions of the world. For monitoring and evaluation of various index used. Variable in this study were employed to examine the phenomenon of drought and wet years consist of SPI, PNPI and NITZCHE. therefore, In this research, annual precipitation data of 6 weather station in the province of North, Razavi and South khorasan for a period of 30 years (1981-2010) analyzed the rainfall and the dry and wet years were studied. Using different methods and comparing the results showed most of the years were normal or dry and very dry or wet conditions were rarely observed according to the reluts. The Standardized precipitation Index (SPI) was recognized better and more accurate comparing to the other indexes because of Stronger capabilities in seprating dry and wet classes and higher sensivitivity to precipitation variation in Khorasan Province.