Trend Analysis of Maximum flood in the Karkheh basin

Floods and droughts are two Extreme phenomena that will always happen in most parts of the world with different frequencies. The occurrence of extreme climate phenomena has been one of the major challenges in the world. Karkheh River is one of the western rivers of Iran that in times of flooding causes huge human and infrastructure damages. The purpose of the present study is to investigate the trend of floods in the Karkheh basin to identify their increase or decrease trend. Detection and analysis of flood trends in Karkheh basin during the period of 1966 -2019 was performed on the precipitation data of 48 stations and daily discharge data of the Mazhin station by parametric (regression line) and nonparametric methods (Man -Kendall test). Drought analysis of the basin showed that this basin had a severe drought with a period of 10 years (2005 – 2015) which has had a great impact on reducing the discharge and occurrence of floods in the region. Besides, the results of the repeatability of precipitation with the Markov Chain Model showed that the occurrence of droughts in the Karkheh basin is always more likely than other events. Although annual rainfall has a declining trend, maximum daily rainfall at most of the basin has an increasing trend. Analysis of the floods trend showed that the frequency of floods has two different periods. Most occurrences of floods (22 cases in 1969 and 15 cases in 1972) in the period (1966-1991) and is the lowest occurrence of floods Related to the course (1992-2019) But what is important Floods events with greater magnitude for the first time in the second course. So that floods with an instantaneous discharge of more than 5000 and 9000 m3 occurred in the second period. Another result of this research is the time displacement of flood events So that until 1992 Of the 64 floods, 53 occurred in April, But after 1992 floods occurred one month earlier in March(The decade 1992 – 2001), in February(The decade 2001 – 2011) and the third decade in January.