ORIGINAL PAPER Streamflow trend analysis by considering autocorrelation structure, long-term persistence, and Hurst coefficient in a semi-arid region of Iran Reza Zamani 1 & Rasoul Mirabbasi 2 & Sajjad Abdollahi 1 & Deepak Jhajharia 3 Received: 1 September 2015 /Accepted: 24 January 2016 # Springer-Verlag Wien 2016 Abstract Due to the substantial decrease of water resources as well as the increase in demand and climate change phenomenon, analyzing the trend of hydrological parameters is of paramount importance. In the present study, investigations were carried out to identify the trends in streamflow at 20 hydrometric stations and 11 rainfall gauging stations located in Karkheh River Basin (KRB), Iran, in monthly, seasonal, and annual time scales during the last 38 years from 1974 to 2011. This study has been con- ducted using two versions of Mann–Kendall tests, including (i) Mann–Kendall test by considering all the significant autocorre- lation structure (MK3) and (ii) Mann–Kendall test by consider- ing LTP and Hurst coefficient (MK4). The results indicate that the KRB streamflow trend (using both test versions) has de- creased in all three time scales. There is a significant decreasing trend in 78 and 73 % of the monthly cases using the MK3 and MK4 tests, respectively, while these percentages changed to 80 and 70 % on seasonal and annual time scales, respectively. Investigation of the trend line slope using Theil –Sen’ s estimator showed a negative trend in all three time scales. The use of MK4 test instead of the MK3 test has caused a decrease in the signif- icance level of Mann–Kendall Z-statistic values. The results of the precipitation trends indicate both increasing and decreasing trends. Also, the correlation between the area average streamflow and precipitation shows a strong correlation in annual time scale in the KRB. 1 Introduction Human activities have led to significant changes in the global water resources within the past few decades and may have affected the hydrological cycle and various hydrological pro- cesses. The considerable decrease in precipitation and changes in the precipitation patterns along with the rise in surface air temperature are one of the most obvious effects of the human- induced climate change. The global warming and climate change have altered the regional hydrological cycles and have subsequently changed the streamflow regimes. Determining the changes in hydrological cycle and evaluating the influence of the human activities on changing climate is one of the key elements in the sustainable development, management, and planning of water resources (Zhang et al. 2011). It is essential to identify and interpret the trends and changes in hydrological and hydro-meteorological variables for developing successful water resource policies at local, regional, and national levels (Wilson et al. 2010). Recently, many investigations have been carried out to determine the significance of observed trends in hydrological and climatic time series, including the changes in temperature and precipitation (e.g., Xu et al. 2010; Marofi et al. 2010; Saboohi et al. 2012; Tabari et al. 2014; Khalili et al. 2015). Many parameters such as the annual streamflow, the sea- sonal distribution of the streamflow, and the magnitude and frequency of floods and droughts will be affected by the anthropogenic-induced climate change, which may have sig- nificant influence on water management, agriculture, * Reza Zamani rzamani.am@gmail.com 1 Department of Hydrology and Water Resources, Faculty of Water Sciences Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran 2 Department of Water Engineering, Shahrekord University, Shahrekord, Iran 3 Department of Agricultural Engineering, North Eastern Regional Institute of Science and Technology, Nirjuli, Arunachal Pradesh 791109, India Theor Appl Climatol DOI 10.1007/s00704-016-1747-4