Contributions of climate change and human activities to the changes in runoff increment in different sections of the Yellow River

The runoff of many rivers in arid and semi-arid regions around the world has decreased remarkably with climate change and enhanced human activities, causing severe challenges in water resources utilization and ecological development. The runoff change in the Yellow River, a typical large river in the arid to semi-arid region, has been studied extensively. However, the spatial and temporal pattern of the runoff variations along the river is still not clear and the contributions of climate change (precipitation and evapotranspiration) and human activities to the runoff changes are not quantified. The purpose of this study is to identify the turning years of the changes in runoff increment for seven sections (above Tangnaihai, Tangnaihai-Lanzhou, Lanzhou-Toudaoguai, Toudaoguai-Longmen, Longmen-Tongguan, Tongguan-Huayuankou and Huayuankou-Lijin) in the Yellow River based on the annual observed data in 1950-2009. These turning years were used to divide the entire period into the baseline period and the measurement period, and calculate the contributions of climate change and human activities to the runoff increment changes in the measurement period. The methods used in this study include cumulative anomaly, linear regression, and the improved method of slope change ratio of cumulative quantity (SCRCQ). Results indicated that the turning years of the runoff increment change were 1989 for the section above Tangnaihai, 1985 for the sections of Tangnaihai-Lanzhou and Lanzhou-Toudaoguai, 1979 for the section of Toudaoguai-Longmen, 1985 for the sections of Longmen-Tongguan and Tongguan-Huayuankou, and 1971 for the section of Huayuankou-Lijin. The contributions to the runoff increment changes in the measurement period from precipitation were 11.98%, 10.02%, 16.60%, 28.49%, 19.24%, 9.45%, and 0.83%, from potential evapotranspiration were -1.32%, -1.61%, -7.37%, -7.74%, -5.82%, -0.96%, and -3.17%, and from human activities were 89.34%, 91.59%, 90.77%, 79.25%, 86.58%, 91.59% and 102.34%, respectively for these seven sections. For the entire runoff change of the whole Yellow River, the total contributions from precipitation were 11.76%, from potential evapotranspiration were -3.83%, and from human activities were 92.07%. These results suggest that human activities have been a dominant influencing factor in the runoff changes not only for each section, but also for the whole river basin since the 1980s. (C) 2012 Elsevier Ltd and INQUA. All rights reserved.