Figure 1 (a) is a distribution map of new land degradation areas along the China-Mongolia Railway (Mongolia section) from 1990 to 2010. Table 1 shows the area and proportion of new land degradation areas along the China-Mongolian. The new land degradation areas between 1990 and 2010 are shown mainly in the south-eastern part of east Gobi province, western Sukhbaatar, southern Kent, northern Gobi Sumubel, northern central Gobi province, southern border of central province and western border of Bulgan province, the total area of land degradation is approximately 43970.60 km2, accounting for about 10.57% of the total area within 200 km on both sides of the China-Mongolia Railway. Among them, the main forms of land degradation are degradation of land-degradation-free areas into desert grasslands, desert grasslands into bare land and land-degradation-free areas degenerated into bare land. Degradation of land-degradation-free areas into desert grasslands is the largest area, about 20091.10 km2, accounting for 45.69% of the total land degradation area, mainly distributed in the northern part of the central Gobi province, southern Kent, the southern border of central province and the western border of Bulgan province. Degradation of desert grasslands into bare land area is the second, about 17771.30 km2, accounting for 40.42% of the total land degradation area, mainly distributed in the south-eastern Gobi province, the western part of Sukhbaatar province, the south-eastern part of Kent province, the northern part of Gobi Sumubel province and the central part of the central Gobi province. Degradation of land-degradation-free areas into bare land is approximately 5304.79 km2, accounting for 12.06% of the total land degradation area, which is scattered in the south-eastern part of the eastern Gobi province, the central province of the northern Gobi province and the northern part of Kent. At the same time, about 23,164.56 km2 of land in the area was restored to varying degrees, and the land restoration area accounted for 5.57% of the total area of the area. The main forms of land restoration are from desert grassland to land-degradation-free areas, from bare land to desert grassland and bare land-degradation-free areas. Desert grassland to land-degradation-free area was the largest one, approximately 11010.90 km2, accounting for 47.53% of the total land restoration area, mainly distributed in the scattered areas of the north-western province of Sukhbaatar, south-eastern Kent and the western part of central province. Bare land to desert grassland is the second, about 10,232.80 km2, accounting for 44.17% of the total land restoration area, mainly distributed in the eastern part of the eastern Gobi province, the south-western Sukhbaatar and the north-eastern part of the central Gobi province. The area of land degradation-free area recovered from bare land is approximately 1745.03 km2, accounting for 7.53% of the total land restoration area, mainly distributed in the scattered areas of central Kent and north-eastern Bulgan.
Figure 1(b) is a distribution map of new land degradation areas along the China-Mongolia Railway (Mongolia section) from 1990 to 2015. The new land degradation areas between 1990 and 2015 are shown mainly in the south-eastern part of east Gobi province, western Sukhbaatar, southern Kent, scattered areas in eastern Kent, northern central Gobi province, southern border of central province and western border of Bulgan province, the total area of land degradation is approximately 58337.26 km2, accounting for about 14.02% of the total area within 200 km on both sides of the China-Mongolia Railway. Among them, the main forms of land degradation are degradation of land-degradation-free areas into desert grasslands, desert grasslands into bare land and land-degradation-free areas degenerated into bare land. Degradation of land-degradation-free areas into desert grasslands is the largest area, about 32574.35 km2, accounting for 55.84% of the total land degradation area, mainly distributed in the southern and eastern Kent, southern central province border, central province north sporadic area and the western border area of Bulgan province. Degradation of desert grasslands into bare land area is the second, about 13862.02 km2, accounting for 23.76% of the total land degradation area, mainly distributed in the south-eastern Gobi province, the western part of Sukhbaatar province, central Gobi province and south-east Kent. Degradation of land-degradation-free areas into bare land is approximately 9541.76 km2, accounting for 16.36% of the total land degradation area, which is scattered in the southern Kent, north central Gobi and central province southern border areas. At the same time, about 34069.38 km2 of land in the area was restored to varying degrees, and the land restoration area accounted for 8.19% of the total area of the area. Among them, the main forms of land restoration are the three types of land-free grasslands, three areas where the desert grasslands are restored to land-free and the land-degradation-free areas are restored from desert grasslands. The area from the bare land to the desert grassland is the largest, approximately 18710.99 km2, accounting for approximately 54.92 % of the total land restoration area, mainly distributed in the south-western province of Sukhbaatar, the northern part of the eastern Gobi province and the south-eastern part of the central Gobi province. The area restored from desert grassland to land-free area is the second, about 11330.70 km2, accounting for 33.26% of the total land restoration area, mainly distributed in the scattered areas of the north-western province of Sukhbaatar, south-eastern Kent, the north of the central Gobi province and the south-western part of the central province. The area of land degradation-free area recovered from bare land is approximately 3586.15 km2, accounting for 10.53% of the total land restoration area, mainly in the north-eastern part of the central Gobi and north-eastern Bulgan provinces.
Figure 1 shows the distribution pattern of desertification along the China-Mongolia Railway (Mongolia section) in 2015, and Table 1 shows the desertification area and proportion statistics along the China-Mongolia Railway (Mongolia section). As can be seen from the map, the area without desertification is mainly distributed in the northern part of the China-Mongolia Railway (Mongolia section), which specifically distributed in the eastern part of Kusugur province, the north-eastern part of the post-Hangai province, Bulgan province, Orkhon province, Serang province, eastern Darhan, northern and southern parts of the central province, Ulaanbaatar,north-west of Gobi Sumubel province, and north and west of Kent. The area of desertification-free area is about 189,010.03 km2, accounting for 45.42% of the total area of the study area. The desertification areas are mainly distributed in the scattered areas in the south, central, eastern and northern parts of the China-Mongolia Railway (Mongolian section), covering an area of 222,604.92 km2, accounting for 53.49% of the total area of the study area. Among them, the slight desertification areas are mainly distributed in the form of flakes scattered along the northern and central parts of the China-Mongolian Railway (Mongolian section), which are distributed in the western border of Bulgan province, southeast of Bulgan province, north-central part of Selangor province, west of Darhan city, central and southern central province, southwestern and eastern parts of Kent, northwestern Sukhbaatar, and northeastern Central Gobi. The area of slight desertification is about 50,928.1 km2, accounting for 12.24% of the total area of the study area. The moderate desertification area is distributed in the central part of the China-Mongolian railway (Mongolian section), which is distributed in the southern border of the central province, the northern part of the central Gobi province, the southeastern part of the Gobi Sumubel province, the southeastern part of Kent, southwestern of Sukhbaatar province, northern east of Gobi province and scattered areas in the east. The area of moderate desertification is about 58,978.85 km2, accounting for 14.17% of the total area of the study area. The severe desertification areas are mainly distributed in large blocks in the southern part of the China-Mongolian railway (Mongolian section), which are distributed in the central and southern parts of the central Gobi province, the southern border area of Gobi Sumubel province, east Gobi province, Sukhbaatar, southwestern province. The area of severe desertification is about 106,216.68 km2, accounting for 25.52% of the total area of the study area. The extremely severe desertification areas are mainly distributed in small areas and scattered in the central part of the central Gobi province and the central part of the east Gobi province. The area is about 6481.29 km2, accounting for about 1.56% of the total area of the study area.The sandy land is concentrated in the central part of the east Gobi province and the central part of the central Gobi province, which is associated with extremely severe desertification areas, with an area of approximately 4545.05 km2, accounting for 1.09% of the total area of the study area.
Based on the interpretation of remote sensing images, data on land cover types in 1990, 2010 and 2015 along the China-Mongolia Railway (Mongolian section) were obtained. The data of 1990 and 2010 are based on Landsat TM image, and the same threshold is used for NDVI, NDWI, NDSI and other sub-indexes, and the two-stage interpretation output is completed simultaneously. Data for 2015 are based on Landsat OLI images, which are set at the same threshold as the 1990 and 2010 methodologies and technical processes. The results show that the overall classification accuracy of land cover products in 1990 was 82.26%, the overall classification accuracy of land cover products in 2010 was 92.34%, the overall classification accuracy of land cover products in 2015 was 92.75%. The area of land cover type in the study area is shown in Tables 1 and 2, and the spatial distribution is shown in Figure 1. Figure 1 (a) shows the distribution of land cover along the China-Mongolia Railway in 1990 (Mongolia). The desert grasslands within 200 km of the Central Mongolia Railway are shown mainly in the northern part of the central Gobi province, the northern part of Gobi Sumubel, the south-eastern part of Kent, the western part of Sukhbaatar and the south-eastern part of the eastern Gobi province. Bare land is mainly distributed in the southern part of the Gobi Sumubel province, the eastern Gobi province, the eastern Gobi province and the southwest corner of the Sukhbaatar province. Sandy land and deserts are concentrated in the central part of east Gobi. The area of bare land in the range of 200 km, 100 km and 50 km on both sides of the railway is the largest, followed by desert grassland. The area of desert grassland is the largest in the range of 30 km, 10 km and 5 km, followed by bare land.
Figure 1 (b) shows the distribution of land cover along the China-Mongolia Railway traffic (Mongolia section) in 2010. It can be seen from the figure that the distribution characteristics of land cover along the China-Mongolia Railway traffic in 2010 are similar to that of 1990. Desert grasslands are mainly distributed in the northern part of the central Gobi province, in the central part of Gobi Sumubel, in the southern part of Kent, in the southwestern part of Sukhbaatar and in the sporadic areas of western Bourges. The bare land is mainly distributed in the southern part of the central Gobi province, the province of Gobi Sumubel, the eastern Gobi province and the western part of Sukhbaatar province. Sand and deserts are concentrated in the central part of the eastern Gobi province. On both sides of the railway 200 km, 100 km, 50 km, 30 km, 10 km, 5 km range of bare land area the largest proportion, the desert grassland is the second.
Figure 1 (c) shows the distribution of land cover along the China-Mongolia Railway transportation line (Mongolia section) in 2015. It can be seen from the 2015 Mid-Mongolia Railway within 200 km of the desert grasslands are mainly distributed in the western province of Sukhbaatar, the southern central province and the northern border of the central Gobi province, the eastern part of Gobi Sumubel province, the southern part of Kent and the western part of Burgan province. Bare land is mainly distributed in the east Gobi province, southwestern Sukhbaatar province, and the southern and eastern parts of the central Gobi province. Sandy areas and deserts are concentrated in the central part of the east Gobi province and southwest of the province of Sukhbaatar. The area of bare land in the range of 200 km, 100 km, 50 km, 30 km, 10 km and 5 km on both sides of the railway is the largest, followed by desert grassland.