Comparison of different approaches to seprating human and climatic impacts on runoff changes in basins

Climate variations and human activities are among the most important factors affecting water resources and have played a major role in river flow changes over the past decades. Therefore, determining the contribution of each of these two factors to river flow changes can help to manage regional water resources in policy and development of consistent strategies. To determine the contribution of each of the human and climatic factors in river flow changes, there are different approaches that each of these approaches have their own assumptions and uncertainty resources in determining the contribution of each of the factors. Accordingly, in this study, using three conventional approaches used to distinguish between human and climatic effects including data-driven modeling, statistical and analytical, the contribution of human and climatic impacts to changes in runoff in the Karkheh dam basin and its four main sub-basins during the period 1980-2014 is estimated and the range of results changes and the sensitivity and reliability of their results have been analyzed. The results show that all three approaches are sensitive to the duration of the statistical period and the extreme events and the high range of uncertainty in their results in terms of the contribution of human activities and climate fluctuations to reducing river flow. So that, The contribution of human activities to reducing river flow, based on these three approaches across the basin, is between 60 to 83 percent, and the contribution of climate variations is between 17 to 40 percent.