1. State Key Lab. of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science; Beijing Normal Univ.; Beijing 100875 China
2. Cold and Arid Regions Environmental and Engineering Research Institute; Chinese Academy of Sciences; Lanzhou 730000 China
3. State Key Lab. of Remote Sensing Science; Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences; Beijing 100101 China
4. Research Base of Karst Eco-environments at Nanchuan in Chongqing, Ministry of Nature Resources; School of Geographical Sciences, Southwest Univ.; Beibei Chongqing 400715 China
5. Institute of Urban Studies, Shanghai Normal Univ.; Shanghai 200234 China
6. College of Resources and Environmental Sciences, China Agricultural Univ.; Beijing 100193 China