1. School of Environment, Beijing Normal University, Beijing 100875, P. R. China
2. Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographic Sciences, East China Normal University, Shanghai 200241, P. R. China
3. Key Laboratory for City Cluster Environmental Safety and Green Development of the Ministry of Education, School of Ecology, Environment and Resources, Guangdong University of Technology, Guangzhou 510006, P. R. China
4. College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, P. R. China
5. State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, P. R. China