1. Assistant Professor, Key Laboratory of West China’s Environmental System (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou Univ., Lanzhou 730000, China.
2. Professor, Key Laboratory of West China’s Environmental System (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou Univ., Lanzhou 730000, China; Professor, Dept. of Geography, Western Michigan Univ., Kalamazoo, MI 49008 (corresponding author).
3. Master Student, Key Laboratory of West China’s Environmental System (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou Univ., Lanzhou 730000, China.