1. Department of Landscape Architecture, California State Polytechnic University, Pomona, CA 91768, USA
2. Department of Landscape Architecture and Environmental Planning, University of California, Berkeley, CA 94720, USA
3. Department of Geography and Department of Statistics, The Ohio State University, Columbus, OH 43210, USA
4. Center for Earth System Science, Tsinghua University, Beijing, 100084, People's Republic of China