1. College of Geography and Environmental Science, Northwest Normal University, Lanzhou 730070, China
2. Key Laboratory of Resource Environment and Sustainable Development of Oasis, Lanzhou 730070, China
3. Gansu Engineering Research Center of Land Utilization and Comprehension Consolidation, Lanzhou 730070, China
4. College of Resources and Environment, Gansu Agricultural University, Lanzhou 730070, China