Assessmentof persistence and recurrence period of drought using standardized precipitation index (SPI) in south Khorasan province (Iran)

Drought is one of the most important environmental disasters,and its frequency in arid and semi-aridareas of Iran is very high. Shortage of rainfall leaves Different effects on groundwater, soil moisture and river flows. Extractionand analysisofIntensity-Continuitycurves are considered as basic requirements for water and agricultural resources managementplanning. Thus Droughtindices have to be used. Standardized Precipitation Index (SPI) is one of the most important indices that is used to determine thelackof rainfall indifferenttime scales. In this paper, drought intensities in a period of 20 years for four stations in South Khorasan in the time scale of 6, 12 and 24 months were determined.Then the changes of the SPI index curves were obtained at different scales. Considering thelongtime scales, medium-term and short-term droughtwere examinedfrom different perspectivesand occurrence ofthe most intenseperiodsof drought andthe time of periodsarecomparedandanalyzed.The results showed thatinmost yearsin theprovinceof Southkhorasandroughtwas occurred.Another result of this study is to clarify the period of droughts. So theaverage calculateddrought period for a lightintensity was3years and thisamountsforan averageintensity ofdroughtswas 3 to4yearsand forseveredroughts, was about 8 to9years.

Keywords:

Drought , SPI , Period