Xiaobo He¹, Yongkang Xue², Yongjian Ding³, Ye Liu⁴ and Shaoyong Wang¹, (1)Northwest institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China, (2)Univ California Los Angeles, Los Angeles, CA, United States, (3)Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China, (4)University of California Los Angeles, Geography, Los Angeles, CA, United States