Trend Analysis of the Streamflow in the Lighvan River hydrometric Stations (Upstream and Downstream)

In recent years, rivers flows have significantly decreased due to regional or global climate change and human activities especially in the arid and semi-arid regions. In this study, the effect of climate change and human activities on the runoff responses was examined using hydrologic model simulation in the Lighvan basin located in the northwest of Iran. For determination of hydrologic model MLR methods (Forward and Ridge) were used. The Mann–Kendall test was applied to identify the trends in hydro-climatic data series. Also, the Pettitt’s test was adapted to detect change-points in the annual discharge values and climatic variables. The results showed that there was negative trend in discharge data series, so that in Hervy station it significant at 10%. Examination of the climatic factors indicated that there was an increase in the temperature values and a decrease in the relative humidity values at the basin. Also all variables related to precipitation in spring have decrease trends. The rapid changes in runoff values and most of the climatic variables occurred in mid-1990s. Comparison of the average discharge in the Hervy Station in the two periods indicates 36% decrease in the recent period compared to the natural period. The effect percentages of the human factors and climatic factors on runoff reduction in all the models used were 65%-84% and 16%-35%, respectively. Therefore, the impact of human activities on the river flow changes was significant.