| The Bayi District,located in the core region of southeast Tibet,is the complicated and active tectonic orogenic junction of Himalayas,Gangdese and Nyenchenthanglha Ranges from south to north.Such typical geologic feature gestates the main rivers along the orogens as Niyang River in the northwest,Yarlung Zangbo River in the south and Palung Zangbo River in the east These rivers cut through the orogens and form the famous high relief landforms with snow covered mountains and canons.As the vapor transport pass of these high relief great Yarlung Zangpo canon,the Indian monsoon could arrive in the Bayi region and bring abundant of rainfall in the summer.Therefore,the Bayi region becomes one of the strongest interactions of the multispheres.Due to its complicated tectonic regime,abrupt topographic change and special climate condition,the Baiyi region is not only the most active tectonic zone but highest relief canons;not only the hotspot of biological diversities worldwide but the ecological fragile area.Considering such important ecological environment importance and fragility,it is necessary to set up a monitoring system to longterm monitor and protect the regional change of the ecology change and environment.This work has importance to implement protection and construction of the state ecological safe shelter zone of the Tibetan Plateau and promote coordinated development between human and nature,and finally practice the green development conviction that lucid waters and lush mountains are invaluable assets.However,such complication of the Bayi region,the traditional methods of the survey and monitoring are far to stratify current comprehensive rends of ecological and environmental changes Remote sensing technology can provide full coverage monitoring service at a spatial and temporal scales,but present research on ecological remote sensing monitoring over Bayi District which is characterized by cloudy and rainy weather together with significant altitude gap is still insufficient.In view of this,this thesis uses Google Earth Engine(GEE)platform and Landsat time series data to extract land use/cover data for Bayi District.Land use and land cover change(LUCC)analysis and landscape pattern change analysis are also implemented.In view of the difficulty in obtaining high-quality remote sensing data over Bayi District,this paper explored the extraction of representative and reliable ecological inversion data from all data sets within a year and then obtained the annual products of vegetation,water body and snow-covered area over Bayi District from 1986 to 2019.Finally,multi-scale correlation analysis method was used to reveal the main driving factors and intensity of ecological evolution in Bayi district.The main results of this study were as follows:1)After preprocessing 24 scenes of Landsat data,five spectral indexes including NDVI,NDWI,NDSI,NDBI and EVI were extracted firstly,and a total of 60 texture feature sets,e.g.ASM,contrast,correlation,variance,IDM,Entropy,from 10 spectral bands were extracted by calculating gray level co-occurrence matrix.Combining spectral features,index features,texture features and terrain data(72witt collection),random forest machine learning algorithm was used to obtain land use/cover products in Bayi District in 1990,1994,2000,2006,2010 and 2018,with general accuracies of 0.95,0.76,0.86,0.88,0.86 and 0.92,respectively.Overall,According to LUCC the land utilization/land cover in Bayi District from 1990 to 2018 is 6 main kinds of types,they are forests related to natural environment,snow land,water,bare land,construction land related to human activity and grassland.Since 1986,the construction land area has been increasing continuously,which is mainly transformed by forest,grassland and water.At the same time,the bare land area also increases year by year,which is mainly formed by the snow melting.2)Upon the vegetation coverage from 1986 to 2019 and the remarkable analysis on the natural environment factors(average temperature,annual precipitation,annual average humidity,annual evaporation capacity,annual average earth temperature)and the human activity intensity factors(population and GDP),it concludes that the vegetation coverage in Bayi District presents the increasing tendency,among that,the high vegetation coverage is expanding(totally increase 1590km~2).Human activity is negatively correlated with the coverage change of low vegetation,medium and low vegetation,medium vegetation and medium and high vegetation.These areas generally focus on the medium and high altitude areas,the vegetation coverage reduces mainly because of the increase of grazing capacity in the alpine meadow areas,the rapid development of industrialization,like road,power grid and travel in medium and high vegetation areas.On the contrary,human activity is positively correlated with the coverage change of no vegetation and high vegetation.on the one hand,it indicates that lots of lands along Yarlung Zangbo River and Niyang Valley transform to the industrial and urban lands because of the city expansion in recent years;on the other hand,it focuses on the ecological environment protection in the city development process,the urban green land and the man-made forests along the rivers are cultivated,which all indicate the green development road of Bayi District in recent years.3)Upon the plateau lake and river extraction from 1986 to 2019 and the remarkable analysis on the natural environment factors(average temperature,annual precipitation,annual average humidity,annual evaporation capacity,annual average earth temperature)and the human activity intensity factors(population and GDP),it concludes that the water coverage in Bayi District was relatively stable before 2014,just fluctuates around 115km~2,but the water area reduces about 10km~2 after 2014.The economic development and construction of Niyang Valley causes the negative relative relation between GDP and water coverage,it is closely related to the hydropower complex damming in Niyang Valley areas in recent years,which causes the decrease of downstream water yield and the highway reorganization and expansion after 2014.4)Upon the inverse analysis on snow coverage space from 1986 to 2019 and the remarkable analysis on the natural environment factors(average temperature,annual precipitation,annual average humidity,annual evaporation capacity,annual average earth temperature)and the human activity intensity factors(population and GDP),it concludes that the snow coverage in Bayi District fluctuates around 500km~2;it is obviously lower than 500km~2 after 2015.The snow coverage is negatively correlated with the annual average temperature,which matches with the global warming and the reduced snow area in Qinghai-Tibet Plateau.At the same time,the temperature in Bayi District increases in 0.34℃/10a,which is the main driving force of reducing the snow area. |
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