[1] China Univ Geosci, Sch Geog & Informat Engn, Dept Geog, Wuhan 430078, Peoples R China
[2] Beijing Normal Univ, State Key Lab Earth Surface Proc & Resource Ecol, Beijing 100875, Peoples R China
[3] Penn State Univ, Populat Res Inst, Dept Agr Econ Sociol & Educ, 112E Armsby, University Pk, PA 16802 USA
[4] Penn State Univ, Social Sci Res Inst, 112E Armsby, University Pk, PA 16802 USA