Determining occurrence pattern of river flow dry and wet periods using Power Laws Analysis in some rivers of West-Azarbaijan

The aim of this study is analyzing the sequential pattern of monthly river flow wet and dry spells in some hydrometric stations (a 20-year period), West-Azarbaijan Province. The wet-dry spells of river flow were determined using Runs theory and the Power Laws Analysis method was used to determine the long-term pattern of low and high flow periods. Then, the drought severity and duration value of wet and dry periods were represented on double-logarithmic plots. Also, the sequence counts of dry and wet periods were determined through 1 to 47-month periods. The results showed that there is an inverse relationship between the severity and persistence of dry periods. The maximum severity of drought was observed in Ghasemlou and Dashbnd stations (0.55 slope of fitted line), and the highest intensity of wet period was related to Pei-Qaleh station (slope of fitted line is 0.6). In other words, the Ghasemlou and Dashbnd stations had the persistent dry periods and Pei-Qaleh station had the highest stability in occurrence of wet periods. The maximum duration of dry and wet periods was observed in Pole-Bahramlou and Sariqmysh stations, respectively having 11 and 15-month average maximum duration occurrence through the studied stations. Also, the results showed that the occurred dry spells over the South parts of the study area had the highest duration and intensity with respect to central and Northest parts of the study area. The results can be used to determine the susceptible area with high drought duration and intense drought periods in planning of surface water resources. The use of power analysis method allows the study of dry and wet periods and also the determination of changes in the behavior of time series of hydrological data due to climate change or human intervention.