Contributions of climate variability and human activities to the variation of runoff in the Wei River Basin, China

The Wei River Basin is a typical arid and semi-arid area of the Yellow River Basin. Quantitative estimates of the contributions of human activities and climate changes in this region will enhance our understanding of the local hydrological mechanism and provide an effective reference for other arid and semi-arid areas of the world in local water resource planning and management. The heuristic segmentation method was used to detect the inflection points of the annual runoff. The slope change ratio of accumulative quantity (SCRAQ) method was applied to compute the relative contributions of human activities and climate changes to the decreasing runoff in the whole basin and the basin above Linjiacun. For the whole basin, when 1960-1969 is selected as the baseline, the contributions of climate changes and human activities in 1970-1993 are 26.47% and 73.53%, respectively, those in 1993-2005 are 23.33% and 76.67%, respectively. When 1970-1993 is selected as the baseline, the contributions of climate and human impacts in 1994-2005 are 18.88% and 81.12%, respectively. The results imply that human activities are the dominant driving factors of runoff reduction, whose effect is increasingly intensifying. Furthermore, in order to verify the contributions of human activities and climate changes based on the SCRAQ method, an approach based on the Budyko hypothesis was used in this paper. The results indicate that the contributions of human activities and climate changes based on the SCRAQ method are consistent with those based on the sensitivity-based method.