Analysis of Hydrological Drought using Constant Threshold Level Method (Case Study: Karkheh River Basin, Iran)

Drought is known as an environmental phenomenon which leads to socio- economic and environmental issues. Therefore its analysis is crucial for proper management and planning of water resources. The Karkheh River basin is one of the important water resources in Iran and that is located in western Iran. Current paper tries to take one step ahead toward scientific and practical drought management in this basin through analyzing hydrological droughts. In this research, daily discharge time series from 13 hydrometric stations were used. The constant threshold level method was applied. Then dry periods were extracted and results were analyzed. The results showed that the largest volume and longest duration of drought in threshold level of 70% mostly happened after 1998. Finally, the suitable probability distribution for the annual maximum series of duration drought and deficit volume at each station was determined. The results revealed that the Johnson distribution is suitable for maximum deficit volume series at 38.5% of stations and the Johnson and Double exponential distributions are suitable for maximum duration series at 23% of stations. Based on the suitable probability distribution, return period of droughts were also computed and the possibility of drought predictions in future was determined.