1. School of Geography and Tourism Shaanxi Normal University Xi'an 710119 Shaanxi China
2. College of Environmental Sciences and Engineering Liaoning Technical University Fuxin 123000 Liaoning China
3. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation Chinese Academy of Sciences and Ministry of Water Resources Yangling 712100 Shaanxi China