Evaluation Of Geological Environmental Carrying Capacity Of Tibet From The Perspective Of NPP

The middle and lower reaches of the Yarlung Zangbo River basin were located in the southeastern part of the Tibetan Plateau.Which was the center of the economic and cultural development of"one river,three rivers",with convenient transportation,rich resources,rapid industrial and economic development,dense population and excellent ecological environment.In recent years,with the economic development,large-scale construction of the region and the complicated geological conditions in the study area,geo-environmental problems such as geological hazards have occurred from time to time.To prevent possible geological and environmental problems in the middle and lower reaches of the Yarlung Zangbo River basin.This study evaluated the geological and environmental carrying capacity of the study area.To provide data support and references for the coordination of regional economic development and environmental protection.This paper collected and analyzed the spatial distribution characteristics of 17indicators in the middle and lower reaches of the Yarlung Zangbo River basin from three aspects:geological environment,ecological environment and social environment.Assigned a graded value to each indicator.Calculated the weights used hierarchical analysis,Critic assignment method and subjective-objective combination assignment method.Constructed a comprehensive multi-indicator evaluation mathematical model.Based on the Arc GIS platform to calculate the carrying capacity of the geological environment in the middle and lower reaches of the Yarlung Zangbo River basin,and to evaluate the carrying capacity in a graded manner.According to the evaluation results,corresponding development countermeasures were proposed.The main results were as follows:（1）Used the geological,ecological and social environment as a guideline layer,a total of 17 indicators were selected,including stratigraphic lithology,geological structure,elevation,slope,slope direction,surface undulation,geological hazards,vegetation cover,rainfall,temperature,total solar radiation,river erosion,soil erosion,mineral resources distribution,population density,GDP per capita and linear engineering.Summarized the characteristics of the spatial distribution and the degree of influence of the indicators.（2）The CASA model was used to estimate the net primary productivity（NPP）of vegetation in the middle and lower reaches of the Yarlung Zangbo River basin over the last 20 years.Analyzed the spatial and temporal distribution characteristics of NPP and evaluation of ecological carrying capacity based on NPP.From 2000 to 2020,the NPP in the study area generally showed a fluctuating upward trend.The mean value of NPP was 279.60 g Cm^-2a^-1 and it fluctuated from 236.13 to 308.60 g Cm^-2a^-1.The spatial distribution of NPP has significant spatial heterogeneity and the characteristics of high in the east and low in the west as a whole.（3）The entropy weight method was used to evaluate the environmental carrying capacity of water resources in the study area.The water resources environmental carrying capacity of the middle and lower reaches of the Yarlung Zangbo River basin was good,with a spatial distribution trend of low in the east and high in the west.The environmental carrying capacity of mineral resources in the study area was evaluated using the kernel density analysis method.The density of mineral resources distribution ranges from 0 to 0.0395 per square kilometers.The environmental carrying capacity was spatially distributed with low east-west and high middle.The area of excellent carrying capacity was the largest,with an area of 23328.80 square kilometers,accounting for 67.04%of the total area of the study area.A soil erosion sensitivity evaluation model was constructed to evaluate the soil resource and environmental carrying capacity of the study area.Soil erosion in the study area was mainly dominated by mildly sensitive and moderately sensitive areas,accounting for49.23%and 44.80%of the total study area respectively.（4）The carrying capacity of the geological environment in the middle and lower reaches of the Yarlung Zangbo River basin was classified into four grades:excellent carrying capacity,good carrying capacity,medium carrying capacity and poor carrying capacity,according to the natural interruption grading method.The area with good carrying capacity was the largest,at 12897.73 square kilometers,accounting for approximately 38.34%of the total study area.The area with excellent carrying capacity was 8869.16 square kilometers,representing approximately 26.30%of the total study area.The area in the carrying capacity was 9025.37 square kilometers,representing approximately 26.92%of the total study area.The area of poor carrying capacity was the smallest,accounting for 8.43%of the total area of the study area.The corresponding countermeasures for the prevention and control of regional geological and environmental problems and economic development were also proposed.