Abstract: The impacts of climate variability and human activities on runoff change in the upper Hanjing River basin and Luanhe River basin, two typical basins of the Middle Route of the South-to-North Water Transfer Project, were investigated with 8 approaches. These are the sensitivity-based approaches (including six Budyko framework based models), precipitation-runoff double mass curves and comparative method of the slope changing ratio of cumulative quantity. The results show that, compared with the baseline period, the average annual runoff in the variation period I/II decreased by 29.5% / 19.1% and 49.8% / 70.0% for the upper Hanjing River basin and Luanhe River basin, respectively. For the upper Hanjiang River basin, climate variability was the main influence factor of runoff reduction in 1991-1999 but human activities was the main influence factor for the period of 2000-2008. The contribution rates of climate variability on runoff reduction became weaker while the contribution rates of human activities on runoff reduction became stronger during the variation period. For Luanhe River basin, human activities was the main influence factor of runoff reduction for the period of 1980-2010, and the contribution rates on runoff reduction by climate variability and human activities almost remained unchanged during the variation period.

Key words: climate variability, human activities, contribution rate of runoff variation, the Middle Route of the South-to-North Water Transfer Project