7 Conclusions
Based on GIS techniques, this study integrated a multi-criteria evaluation approach involving high-spatial-resolution remote sensing data (slope gradient, VFC, and land use) to qualitatively identify the trends in the spatial distribution of soil erosion risk in the middle reaches of the Yellow River Basin from 1978 to 2010.
The results show that erosion risk has decreased over the 33-year study period. From 1978 to 1998, the areas categorized as having extremely severe, more severe, and severe erosion risk decreased by 0.01%, 0.13%, and 0.97% of the study area, respectively; the respective decreases were 0.01%, 0.22%, and 3.41%. The decreasing trend from 1998 to 2010 was more pronounced than that from 1978 to 1998.
The results also indicate that from 1978 to 2010 the total area classed as deterioration grade erosion was smaller than that classed as improvement grade erosion, and that the transformation between these classes between 1998 and 2010 was smaller than that between 1978 and 1998. From 1978 to 1998, the proportions of the region where the erosion grade changed from severe to slight and from severe to light were 0.16% and 0.13%, respectively, and the proportions of regions where the erosion grade changed from slight and light to extremely severe and severe were all less than 0.01%. From 1998 to 2010, the proportions of regions where the erosion grade changed from severe to slight and from severe to light were 0.97% and 1.15%, respectively, and the proportions of regions where the erosion grade changed from slight or light to extremely severe or severe were all less than 0.01%. The proportions of extremely severe and more severe erosion grades were all less than 0.01% of the total area from 1978 to 1998 and from 1998 to 2010, but these values were greater from 1998 to 2010 than from 1978 to 1998.
