Analysis of Drought Characteristics of Tabriz (1951-2015)

In this study, for investigation of Tabriz droughts, monthly precipitation data (1951-2015) were used. Three drought characteristics, including drought duration (Ld), severity (Sd) and magnitude (Md) were extracted from observations. Data of every characteristic fitted with the most suitable statistical distribution. Then five hundred artificial series with the same length of the observed precipitation were generated for each of the characteristics. Two thresholds were considered for drought analysis, including average of annual precipitation and average of annual precipitation minus its standard deviation. The results of first threshold showed that the maximum of Ld, Sd and Md were 7 years, 500 mm and 71 mm/yr, respectively. Poisson, Pearson type 5 and Wakeby distributions were recognized as the most suitable fitted distributions for to the Ld, Sd and Md, respectively. Quantile 90% for Ld, Sd and Md were obtained as 5 years, 443 mm, 103 mm per year, respectively. The maximum and minimum of Ld in Tabriz were between 14 and 71 mm/yr. The second threshold results were showed that the maximum for Ld, Sd and Md were 2 years, 76 mm and 38 mm/yr, respectively. Uniform, Burr, and Generalized Extreme value distributions were recognized as the suitable distributions, for duration, severity and drought magnitudes, respectively. In this case, quintile 90% for drought duration, severity, magnitudes were obtained as 2 years, 51 mm and 38 mm/yr, respectively.