[Dynamics of desertification in the lower reaches of Shiyang River Basin, Northwest China during 1995-2018].

We collected remote sensing images of lower reaches of the Shiyang River Basin in 1995, 2000, 2005, 2010, 2015, and 2018. We analyzed the dynamics of desertification in Minqin County by constructing desertification difference index, using RS and GIS theories and methods. We established the Albedo-NDVI feature space based on the normalized vegetation index (NDVI) and surface albedo (Albedo). The results showed that the desertification area in the lower reaches of Shi-yang River Basin accounted for more than 90% of the total area of the Minqin. Oasis scattered in large areas of desertified land. Moderate desertification accounted for more than 70% of the total area of the county. The area of desertification in Minqin showed an decreasing trend from 1995 to 2018, with an average annual reduction area of 22.06 km2 and an average annual reduction rate of 0.1%. During the study period, various types of desertification area contracted and expanded simultaneously, and the relative changes of severe, moderate, mild, and slight desertification areas were -1.5%, 0.2%, -0.9%, and 3.8% respectively. Those results indicated that the severity of desertification was reduced. The desertification area was generally at a stable state. There was no large-scale desertification process and no obvious trends of desertification. Desertification control had achieved phased results. In the study area, the area where the desertification decreased in a fluctuation way accounted for 15.2%, while the area with increased desertification only accounted for 3.9%. The areas with irregular fluctuations of desertification were mainly distributed in the transitional area of desert oasis and the edge area of oasis, with an area of 17.7% of the total land area. The desertification change was more active in the ecotone of oasis and desert area, which was the key control and repair region in the future.