Mendeley  

Zotero  

mojarad F, kheiri R, Noorisameleh Z. Frequency Analysis of Daily Droughts in Iran by Using Effective Drought Index. jgs 2015; 14 (35) :29-48
URL: http://jgs.khu.ac.ir/article-1-2177-en.html

Iran's Potential for the occurrence of drought at various severities illuminates the need to examine this phenomenon with new indexes. The major deficiency of the current indexes is that they cannot monitor the droughts in daily scale. Effective Drought Index (EDI) overcomes this defect. The goal of this study is to analyze the frequency of daily droughts by EDI in 43 synoptic stations in a 30-year period. Accordingly, the frequency of daily droughts in the stations was calculated by EDI during the seasons and the year. Then the stations were divided into five groups using cluster analysis based on total frequency of mild to most severe droughts (categories 1 to 4), and frequency patterns in each group were examined. The results showed that the most severe droughts have not happened in the stations except for Gorgan, Zanjan and Torbat-Heydariyeh. In contrast, the frequencies of mild, moderate and severe droughts, all being equal, are much more than most severe droughts, and their frequencies are almost equal. In 56 percent of the days, a variety of droughts (mild to most severe) has occurred in the whole country. Based on the output maps, frequency distribution of droughts in the country does not follow a certain geographical pattern, so it could be cocluded that all types of droughts have happened in all regions of the country. However, maximum total frequency of daily droughts (mild to most severe) is observed in the east and center parts. The decrease in the EDI values over time shows the tendency of the most stations towards drought.