Using Run Theory to Analysis of Drought severity - Duration - Return Period (Case Study: Fars Province)

Drought is a consequence of fluctuations in climate conditions that their effect on human societies is more than another phenomenon. For drought investigation, monthly data of precipitation in 9 synoptic stations of Fars province during twenty years period (1995-2014) was used. After calculation of drought severity using run theory, suitable index among DI, PNPI, SIAP, RAI, SPI and BMDI indices was selected. Then time series of drought severity fitted on different distributions and after selection of best distribution for each station, drought severity with duration 2, 4, 6 and 8 months in return periods of 2, 3, 5, 10, 25 and 50 years calculated and related table was prepared. Also using cluster analysis studied stations divided into different groups. At least, drought severity zoning map in 2 decades plotted in GIS. Results showed that Standard precipitation index (SPI) as the best index could be a proper interpret of drought computing. Generally, in study area drought severity increase in the recent decade.