1. State Key Laboratory of Simulation and Regulation of Water Cycles in River Basins, Department of Irrigation and DrainageChina Institute of Water Resources and Hydropower Research Beijing 100048 PR China
2. Department of Biological and Environmental EngineeringCornell University Ithaca NY 14853 USA
3. Development Research CenterMinistry of Water Resources of P.R. China Beijing 100038 P.R. China
4. College of Water Resources and Civil EngineeringChina Agricultural University Beijing 100083 PR China
5. Department of Ecosystem Science and ManagementPennsylvania State University, University Park PA 16802 USA