Spatial and Temporal Changes of Desertification Land and Its Influence Factors in Source Region of the Yellow River from 1975 to 2005

The distribution of desertification land in source region of the Yellow River in 1975 and 2005 was acquired by remote sensing data and GIS technology.There was large area of desertification land in source region of the Yellow River and it was mainly distributed in west,north and south sub-areas of the source region.The increase of desertification land was obvious during 1975-2005.The desertification land increased from 19 297.34 km2 in 1975 to 22 042.32 km2 in 2005,and the percentage of desertification land to total area of the source region increased from 14.68% to 16.77%.The very severe desertification land,severe desertification land,moderate desertification land,light desertification land and potential desertification land increased by 233.27 km2,987.93 km2,336.28 km2,544.8 km2 and 642.7 km2,respectively.There was 3 075.57 km2 desertification land in 2005 came from the non-desertified land in 1975,which accounted for 57.28% of desertification land in 2005,and the other 42.72% came from the development of lower degrees of desertification land to higher ones.Climate change and unreasonable human activities jointly caused the increase of desertification land,and the increase of temperature was main natural factor and over grazing was main anthropogenic factor for the development of desertification.