Dynamic analysis of land use/land cover change in Dunhuang oasis, China

Land use/cover change (LUCC) is one of the core contents of the global change research. As a unique ecological unit in arid and semi-arid area, oasis is a basic premise to maintain the existence and development of local people. In this paper, the rectangular area, where Dunhuang oasis locates, is chosen to study the dynamic change of LUCC over the last 20 years. Landsat5-TM images of 1987, 1996 and 2007 were interpreted by ArcGIS9.2 software. Based on field investigation, the land use type is classified into 6 classes (crop land, water wetland, high coverage grassland, moderate coverage grassland, low coverage grassland and non-vegetation area) to analyze the LUCC, which was showed by transfer matrix. The results showed that the vegetation-coverage was generally increasing over the last 20 years, which is more obvious in the latter 10 years. The area of artificial vegetation in crop land increased significantly by 38.67%. Among natural vegetation, the area of high coverage grassland increased by 83.94% while other four land type classes were decreased. The area of moderate and low coverage grassland decreased by 11.73% and 24.41% respectively. According to the transfer matrix of interpreted data, the conversions were occurred among 6 land use types. The main conversion types are as follows, conversion from low coverage grassland and non-vegetation area to crop land, moderate and low coverage grassland to high coverage grassland, and inter-conversion between low coverage grassland and non-vegetation area. The main reason of vegetation change is the expand use of water resources. Not only the area of irrigated farmland was increased, but also the area of high coverage grassland was enlarged benefiting from infiltration of the surface water in farmland.