1. College of Geographic Science, Qinghai Normal University, Xining 810008, China
2. Key Laboratory of Tibetan Plateau Land Surface Processes and Ecological Conservation (Ministry of Education), Qinghai Normal University, Xining 810008, China
3. Qinghai Province Key Laboratory of Physical Geography and Environmental Process, Qinghai Normal University, Xining 810008, China
4. Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China