1. College of Water Resources and Civil Engineering China Agricultural University Beijing 100083 China
2. Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research Chinese Academy of Sciences Beijing 100101 China
3. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation Chinese Academy of Science and Ministry of Water Resources Yangling 712100 China