Analysis of stream flow drought and deficiency in the west of Iran

Iran is located within the semi-arid and arid climatic zones, characterized by the consistent droughts and shortage of water resource. This paper aims to study the hydrological drought in Karkheh river basin known as one of the main water resources in the west of Iran, in order to hinder the undesirable effects of such events on water resources through understanding its mechanism. For the purpose of this study, 13 stations were selected in the river basin to investigate the hydrological drought, based on the constant and variable threshold level methods. Among the probability distribution methods involving Log-Normal, Weibull, Double exponential distribution, Gamma, Johnson, and Generalized Pareto (GP), the most suitable one was selected using the Chi-square test at each annual maximum series of deficit volume and drought duration. Furthermore, the occurrence probabilities of drought events as well as the return period of droughts were extracted according to the best-fitted probability distribution method. The results based on both constant and variable threshold level methods demonstrated the occurrence of droughts in the most of the studied periods even for a short time. Moreover, the largest deficit volume and the longest drought duration were occurred under both methods in the periods 1999-2000, and 2007-2008.The latest time step was identified as the most critical one within the study period.