Abstract:The oases of Guazhou County (China) play an important role in connecting the western and eastern economies and in developing the Hexi section of the Silk Road. In the present study, remote sensing images (Landsat5TM from 1986, 1990, 1995, 2000, 2005, and 2010 and Landsat8 from 2015) were used to elucidate the distribution of oases in Guazhou. The study area was divided into grids of 90×90 m, and the relative area change (KgridT1-T2) and accumulative area change rate (CKgird) were calculated as the expansion, retreat, or no change in every grid of each study period compared to the grid area and the sum of absolute Kgrid values to reflect the level of change (i.e., weak, strong, acute, none), respectively, over the last 30 years. The qualitative description and classification of these two indicators were used to analyze the spatio-temporal and spatial regularity of changes in Guazhou oases. Our analyses revealed that (1) oasis area expanded consistently and significantly over the last 30 years, by 278.874 km2 (49.6%); (2) oasis expansion mainly occurred after 2000, especially between 2000 and 2005 (38.45%), followed by the period between 2005 and 2015 (19.58%), but was lower before 2000 (12.6%); (3) oases were distributed in three areas, with Changma alluvial plain oases mainly expanding in immigrant towns, mainly to the front and west, the Shule River irrigation oases were scattered outwards based on the origin oasis of every period, and the small and dispersed river tail oases exhibiting relatively large expansion; (4) oases retreat occurred in the Changma alluvial plain, which possessed more natural vegetation, which is easily influenced by environment factors; and (5) oasis expansion has increased over the last 30 years. The Changma irrigation oases, as a typical expansion area, gradually expanded to the northern fine plain; however, due to the shallow water table in the region itself, surface salinization is serious, coupled with a large number of surface water projects generated in oasis development, salinization prevention and control has become an important issue in the region to ensure long-term stable development of oasis to considered.
