Trend Analysis of Precipitation and River Flow in the Qara-Su River Basin

Being aware of decreasing or increasing trend of precipitation and discharge in watersheds has very important role in water resources management and the subjects relating to water engineering. In this study، the trend of precipitation and discharge at Qara-su River Basin in Ardebil has been studied in monthly، seasonal and annual timescales over the period from 1351 to 1382. For investigation of the existence or absence of a trend، Mann-Kendall test was used by detecting effects of all auto correlations coefficients، and Sen’s estimator was used at different significant level to evaluate the magnitude of the test. The results of the calculated values for precipitation and discharge data set indicated that the trend of the Qara-su River discharge was decreasing for both stations in annual timescale. Also، decreasing trend of discharge dataset was found for seasonal timescale in spring، autumn and winter in which significant trend belonged to winter season. Maximum value of decrease for discharge is for Doustbiglo station in spring (-0. 62 m^3/s)، and the minimum value of decrease for discharge in summer for this station، too. Furthermore، there was not significant trend for precipitation dataset in monthly، seasonal، and annual timescales.