School of Geographical Science, Qinghai Normal University, Xining, Qinghai 810008, China;
School of Geographical Science, Qinghai Normal University, Xining, Qinghai 810008, China;
Institute of Soil and Water Conservation, Northwest Agriculture and Forestry University,Yangling, Shaanxi 712100, China;
Department of Computer Science and Technology, Lvliang University, Lvliang, Shanxi 033000, China;