Investigation of total and base flow trend in Arazkuseh hydrometric station (Gorganrood Watershed in Golestan Province)

Base flow reduction in comparison with its average long-term value represents drought conditions but average base flow reduction over specific time indicates the area tends to drought. Mann-Kendall's non-parametric test was used for considering the trend of time series. In this study, Arazkuseh hydrometric station with 40-year-old statistical period has been selected as the case study. After base flow separation from daily discharge's data and preparation of monthly and annual time series, the Mann-Kendall's test has been used for determination of trend. The analysis of trend at the significant level of %5 indicates downward trend in base flow and total discharge average based on annual scale but there is not any trend for maximum of base flow and total discharge. In monthly scale, the trend of average base flow during November, March until June has had downward, but in the rest there is not any trend. Also, average total flow during March until June shows downward trend and in the rest there is not any trend during year. So it maybe concluded that the area tends to drought.