Surveying sandy deserts and desertified lands in north-western China by remote sensing

Sandy deserts and desertified lands (SDDL) cover most of north-western China, and desertification is a severe environmental issue in this region. In this study, we classify SDDL into mobile, semi-mobile, semi-anchored, and anchored classes, and divide the corresponding severity of desertification into four levels: extremely severe, severe, moderate, and slight. Using SDDL databases derived from Landsat TM and ETM images in 1986 and 2000, we discuss the evolution of SDDL and the processes and causes of desertification. The desertified area increased by 16 101 km(2) between 1986 and 2000, and most of the desertified land was classified as severely or extremely severely desertified. However, 3437 km(2) of SDDL were also rehabilitated during this period. The area of SDDL increased in the Qinghai and Xinjiang regions, and in the western part of Inner Mongolia, but decreased in the Shaanxi, Gansu, and Ningxia regions. The causes of desertification differed among regions, and different measures to control desertification are proposed for the different regions.