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

Iran is located within the semi-arid and arid climatic zones, characterizedby the consistent droughts and shortage of water resource. this paper aims tostudy the hydrological drought in karkheh river basin known as one of themain water resources in the west of iran, in order to hinder the undesirableeffects of such events on water resources through understanding itsmechanism. for the purpose of this study, 13 stations were selected in the riverbasin to investigate the hydrological drought, based on the constant andvariable threshold level methods. among the probability distribution methodsinvolving log-normal, weibull, double exponential distribution, gamma,johnson, and generalized pareto (gp), the most suitable one was selectedusing the chi-square test at each annual maximum series of deficit volume anddrought duration. furthermore, the occurrence probabilities of drought eventsas well as the return period of droughts were extracted according to the bestfittedprobability distribution method. the results based on both constant andvariable threshold level methods demonstrated the occurrence of droughts inthe most of the studied periods even for a short time. moreover, the largestdeficit volume and the longest drought duration were occurred under bothmethods in the periods 1999-2000, and 2007-2008.the latest time step wasidentified as the most critical one within the study period.