There are three important aspects of drought, which have to be assessed: intensity, duration and extent. Most of authentic world indexes, such as Standard Precipitation Index (SPI), Percent of Normal (PN), deciles and Palmer Drought Severity Index (PDSI) were designed to clarify intensity and duration of drought. Geographical Information System (GIS) is a very useful tool to determine drought's extent and zoning the iso-intensity regions. In this investigation, PN index was used for zoning drought's intensity in Khorasan Razavi Province. Also long-term time series were used to assess and calculate drought's effects on water resources. Based on PN zoning maps, it can be concluded that more than half of case study's area was faced drought in 32-40% of investigation periods. Also yearly precipitation in different return period's maps shows hardest situation in Torbat-heidarieh, Gonabad, Khaf and Kashmar. Results of time series showed that considerable rainfall of autumn and winter of 1385 did not have any important influence on water resources in Khorasan Razavi Province and therefore could not compensate this region's drought for more than one year period and special management is needed to remove damages.

Key words: Drought, Standard Precipitation Index (SPI), Time Series, Zoning, Intensity