Evolution Of Oases Under Human Interference In Arid Northwest China

Heihe River Basin,Shule River Basin,Shiyang River Basin and the Tarim River Basin are the major inland river basins in arid Northwestern China.In recent years,oasis changed rapidly due to the intensification of human activities.Oasis change directly reflects the effects of human activities on the process of ecological evolution.Base on the land use data from 2002 to 2012,the oases evolution process in Heihe River Basin,Shule River Basin,Shiyang River Basin and the Tarim River Basin is studied.Based on the hydrological data and meteorological data,the driving mechanism of natural oases in middle-lower reaches of Heihe River is analyzed.The dominant driving factors of artificial oases in the middle reaches of the Heihe River Basin are identified from natural driving factors and socio-economic driving factors.The main results of this study are as follows:(1)In principle,oases in Heihe River Basin,Shule River Basin,Shiyang River Basin and the Tarim River Basin are expanding from 2002 to 2012.The natural oases are relatively stable during the entire study period,while the artificial oasis are relatively unstable.In general,artificial oases are rapidly expanding,which reflects the effects of human activities on oases.(2)The gravity center of oasis moves downstream in Heihe River Basin,while the gravity center of oasis moves upstream in the Shule River Basin.From 2004 to 2006,the gravity center of oasis moves downstream in Shiyanghe River Basin.From 2006 to 2012,the gravity center of oasis moves upstream in Shiyanghe River Basin.During the transformation between oasis and desert,grassland and woodland contribute more than other land use types.During the transformation between natural oases and artificial oases,the transformation from natural oases to artificial oases dominates.(3)The study on the driving mechanism of natural oases shows that groundwater depth is the dominant driving factor of natural oasis in middle-lower reaches of Heihe River Basin.By driving the distribution of vegetation coverage,groundwater depth influences the evolution of natural oases.The correlation model between groundwater depth and vegetation coverage is established in this study.It is found that the vegetation coverage decreases with increasing groundwater depth.And this process can be divided into three different stages by groundwater depth: 0~2.3m,2.3~6.8m and 6.8~7.3m.These three different stages correspond to different dominant vegetation types.(4)The study on the driving mechanism of artificial oases shows that the evolution of artificial oases is influenced by natural driving factors and socio-economic driving factors.Agricultural technology level,rural socio-economic development level and policy factors are the dominant driving factors during the research period.