The Calculation of Continuity and Intensity of Droughts using Modified SPEI Index (Case study: Tabriz and Urmia Cities)

The Calculation of Continuity and Intensity of Droughts using Modified SPEI Index (Case study: Tabriz and Urmia Cities) Marhamat Sebghati*1, Hesam Ahmadi2 and Alireza Moghaddam3 1M.Sc. Faculty of Natural Resources (Watershed Managment), Urmia University, Urmia, Iran 2Assistance Prof. Faculty of Natural Resources (Watershed Managment ), Urmia University, Urmia, Iran 3PhD Candidate of Water Resources Engineering, Urmia University, Urmia, Iran *Corresponding Author: [email protected] Abstract In recent years, global climate change and increasing drought are the important environmental issues, and many studies have been done about these issues. In this research, continuity and intensity of drought for Tabriz and Urmia cities, during 31 years period, using corrected SPEI index by Penman-Monteith FAO method was investigated. Mmoving average of 3, 6 and 12 month for monitoring rainfall trend was used comparison. The results showed that SPEI index in both cities were mainly faced with drought conditions. In addition, analysis of the moving average, drought index and statistical distributions of wet and dry years showed same results in most years for both citis. The most intensive drought index derived for Tabriz and Urmia stations were equal to -2.75 and -2 respectively. The longest drought indicated for both cities was within 2005 to 2010. Keywords: Statistical distributions, drought, SPEI Index, moving average, Penman-Monteith FAO.