| Desertification has become one of the most serious ecological and environmental problems in the world.And because of its wide distribution,it harms the natural environment,ecological environment,social economy and the survival and development of human beings,which has attracted the attention of the international community.It is of great significance for the control and prevention of desertification to carry out the research on the monitoring,driving factors and evolution rules of desertification,especially the analysis and research on the driving factors of desertification on this basis.The problem of desertification in the middle and lower reaches of Shule River is serious,and the ecological environment is fragile.Understanding the characteristics of desertification evolution and influencing factors is the premise to maintain and improve the regional ecological environment and ensure the social and economic development.Therefore,this paper takes desertification land in the middle and lower reaches of Shule River as the research object,based on Landsat5 TM?Landsat7 ETM+ and Landsat8 OLI remote sensing image data,extracts the Albedo and NDVI data of the middle and lower reaches of Shule River in 1987,1992,1997,2002,2007,2012 and 2017,constructs the differential index model(DDI)of desertification remote sensing monitoring,and analyzes its temporal and spatial dynamic change characteristics and influencing factors.The main findings are as follows:(1)In the time dynamic change,Between 1987-1992,1992-1997,1997-2002,2002-2007,2007-2012 and 2012-2017,surface albedo(Albedo)decreased,decreased,decreased,decreased,increased in the middle and lower reaches of the Shule River,the corresponding rates of change were-0.25%,-0.25%,-4.83%,-1.6%,-6.52%,2.55%,respectively;Vegetation index(NDVI)showed a trend of decline,increase,increase,increase,increase and increase,with corresponding change rates of-5.95%,0.6%,0.89%,5.34%,14.83% and 0.24%,respectively.Desertification index(DDI)showed a trend of decreasing,decreasing,increasing,decreasing,increasing and increasing,and the corresponding change rates were-2.85%,-4.53%,22.68%,-3.02%,12.81% and35.77%,respectively.It can be seen that from 1987 to 2017,Albedo fluctuated downward,NDVI fluctuated upward,and DDI fluctuated upward,indicating that desertification in the study area generally showed a weakening trend.(2)In the change of grade,between 1987 and 2017,the surface albedo(Albedo)in the middle and lower reaches of the Shule River was dominated by relatively low grade,accounting for more than 75%,followed by middle grade,accounting for more than10%,while the other grades accounted for less than 10%,with low,relatively low,middle,relatively high and high grade area variations of 5.52%,-0.54 %,-5.13%,0.14%,about 0.001%,respectively,and the area of grade surface albedo shifted mainly to relatively low grade.The vegetation index(NDVI)grade was mainly low vegetation cover grade,the proportion was above 85%,followed by middle vegetation cover grade,the proportion was less than 11%,the proportion of high vegetation cover grade was the smallest,less than 2%,the proportion of change of low,middle and high vegetation cover grade area in 1987-2017 was-2.04%,1.86%,0.18%,and the low vegetation cover area was transferred to middle and high vegetation cover.The desertification index(DDI)was mainly severe and moderate,with more than 29%,followed by mild and extremely severe,with more than 9% and no more than 5% of non-desertification areas,the percentage of changes in the area of extreme severe,severe,moderate,mild and non-desertification in 1987-2017 was-7.52%,-7.85%,-0.3%,13.44% and 2.23%,respectively,obviously,the grade of desertification in the study area generally shifted from extremely severe and severe grade areas to mild and non-desertification.(3)In space change,The spatial variation of surface albedo in the middle and lower reaches of Shule River from 1987 to 2017 was mainly low,and it was mainly distributed in the middle and south of Dunhuang City,and it was evenly distributed in other counties.The change of vegetation cover was stable and increasing,mainly in the middle and south of Dunhuang city,the middle of Guazhou county and the middle and south of Yumen city.The change of desertification in the middle and lower reaches of Shule River was mainly stable and reversed,which was concentrated in the middle of Dunhuang City,the north and south of Guazhou County,while the distribution ofYumen City and Subei County was scattered,and the development trend of desertification was sporadic in the middle and east of Guazhou County and the south of Subei County.(4)Cause analysis shows that,Desertification in the middle and lower reaches of the Shule River is affected by natural and human factors,among which temperature,precipitation,evapotranspiration and sunshine hours are the main natural factors affecting desertification,and its cumulative contribution rate has reached 88.78%.Water body,cultivated land and forest land are the most important factors affecting desertification in the change of land use type,among which the area of cultivated land and forest land has increased significantly,27.37% and 20.01% respectively.GDP,primary industry,secondary industry and tertiary industry are the main social and economic factors that affect land desertification,and their principal component contribution rate is 85.98%.In terms of the influence degree of natural factors and human factors,human factors have a greater influence on land desertification than natural factors,contributing 64.47% and 26.04% respectively.Human factors are the most important factors affecting land desertification in the middle and lower reaches of Shule River. |
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