1. Associate Professor, Laboratory for Earth Surface Processes, Ministry of Education, College of Urban and Environmental Sciences, Peking Univ., Beijing 100871, China (corresponding author).
2. Postgraduate Student, Laboratory for Earth Surface Processes, Ministry of Education, College of Urban and Environmental Sciences, Peking Univ., Beijing 100871, China.
3. Ph.D. Candidate, Laboratory for Earth Surface Processes, Ministry of Education, College of Urban and Environmental Sciences, Peking Univ., Beijing 100871, China.
4. Postgraduate Student, Graduate School of Architecture, Planning, and Preservation, Columbia Univ., NewYork, NY 10027.