Assessment of spatial and temporal variation of seasonal and annual streamflow in Karkheh River Basin

Land use and climate change can alter the seasonal and annual discharge of rivers. Annual and seasonal river discharge changes should be considered in the management and planning of water resources in basins. For this propose, Karkheh basin was selected for study. For trend analysis of this basin daily discharge time series in 15 sub-basins during the 1969-2012 period. After reconstruction of time series of selected sub-basin, five discharge indicators including seasonal and annual Q5, Q10, Q50, Q90 and Q95 were prepared for future analyses. The seasonal an annual discharge trends were calculated using Thiel-Sen method, then discharge percent changes in the 1969-2012 for selected sub-basins were determined and seasonal and annual discharge map for each indicator was prepared. The result showed that seasonal and annual discharge in most selected sub-basin had decreasing and negative trend. The selected sub-basin in the southeast had less decreasing trend relative to other ones. Low flow (Q5, Q10) relative to high flow (Q90, Q95) had steeper decreasing trend. The spring high flow indicator related to Kakareza and Afrineh sub-basins had increasing trend. These two sub-basins were independent and are not influence by any other runoff. The increase in high flow in these two sub-basins can be caused by increase in temperature due to climate change and early snow melting in recent years