1 Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographic Sciences, East China Normal University, Shanghai 200241, China.
2 Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China.
3 Technical Centre for Soil, Agriculture and Rural Ecology and Environment, Ministry of Ecology and Environment, Beijing 100012, China.
4 College of Environmental Natural Resource Sciences, Zhejiang University, Hangzhou 310058, China.
5 State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
6 School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
7 Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographic Sciences, East China Normal University, Shanghai 200241, China. Electronic address: mliu@geo.ecnu.edu.cn.