| The Turpan Oasis is located in the center of the Turpan Basin,where the climate is dry,precipitation is scarce,and the ecological environment is fragile.With the national economic development strategy paying more and more attention to the arid regions in the northwest,the level of social and economic development of the oasis is gradually improving,and the development and utilization of water and soil resources in the oasis in the arid regions is increasing.The large-scale development and utilization of water and soil resources as well as the long-term farming activities,on the one hand,promoted the development of the oasis,on the other hand also caused a series of ecological environment problems,such as desertification,salinization disasters.This paper studies the temporal and spatial changes of the Turpan Oasis in recent years,and analyzes the driving mechanism from natural factors and human factors,providing a scientific basis for the rational development and utilization of oasis resources and ecological restoration.Taking the Oasis in Turpan as the research object,based on the Landsat data of the long-term sequence,the supervised classification,the normalized vegetation index method combined with the normalized index,texture analysis,and decision tree method are used to extract the oasis information.From the perspective of the number of oasis and the distribution of time and space,the process of changing oasis in Turpan City is analyzed in combination with oasis dynamics,cumulative change rate,center of gravity migration and landscape pattern change.The natural and socio-economic drivers of the changes in the oasis were discussed and the following conclusions were drawn.(1)On the basis of natural oases,the oasis in Turpan City has gradually developed into a natural-artificial oasis.The artificial oasis occupies the main body of the oasis,while the natural oasis accounts for a very small proportion,distributed in the periphery of the artificial oasis.(2)Oasis area is generally expanding and expansion speed experienced a fast-slow-fast change.From the regional point of view,the Oasis in Gaochang District has the largest expansion area and the fastest expansion rate,followed by Toksun and Shanshan.During the entire study period,the unaltered areas of the oasis accounted for the main body,and the expansion and retreat occurred mostly at the edge of the oasis—the natural oasis area.The oasis expansion and retreat area along the river and around the township are relatively small,and the oasis is relatively stable.Oasis expands significantly in the transition zone between Artificial oasis and natural oases in the south and east,and retreats in natural oasis areas far from towns and villages.In the oasis change region,the weak change region accounts for the smallest proportion,and is mostly distributed at the edge of the oasis and around the township;the regions with strong change accounted for the largest proportion,mainly distributed in the lower reaches of the river,the transition zone between natural oasis and artificial oasis;the regions with drastic changes were distributed in the outermost periphery of the oasis-the natural oasis area.In the past 23 years,the focus of Oasis in Turpan City has shifted to the north,with a short transfer distance.It has been located in Gaochang District,the core of Turpan City.The Oasis Landscape Index tends to be stable during fluctuations.The fragmentation degree of the oasis landscape has a downward trend as a whole,the boundary tends to be regular,the internal connectivity is enhanced,and the landscape distribution is more uniform.The impact of human activities on the oasis is growing.(3)Many factors promote the change of oasis.The basic role is the natural factors such as climate background,topography,soil geology,water resources distribution and natural disasters in the arid area.The decisive factors are the socio-economic drivers of social and economic levels,water conservancy facilities,mechanization levels,and policies. |
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