assessment and comparison of multiple index climatic droughts and determine the best index in central iran

the aim of this research is to analyze the performance of 8 drought’s index in isfahan, kerman and yazd province and choose the best index. for this purpose, used monthly and yearly rainfall data in the period of 30 years (1985-2014) and also used 8 drought indexes in 20 meteorological stations of central iran which the accuracy of each index in determining drought is examined. also zoning in arc gis 9.3 has done for driest year in the time period. and it has performed according to the best selected index. for choosing the best index in annual and monthly scale has used the efficient measure of minimum precipitation occurrence year with severe droughts in region’s stations. the results showed that in the monthly scale only 6 and 12 months of spi index in order to analyze the drought even in low rainfall months which confront with zero data contains. in this temporal scale, static indexes such as rai and di in all the stations showed the minimum precipitation year according to severe droughts and named as the best index. also the weakest index belonged to niche that had not the ability of determining the drought intensity in all the study’s region. in comparison the performance of rai and spi determined which rai index showed the severe drought in all the study’s region but spi index could not show the severe drought category in the period of 30 year in the region of central iran in some stations.