Analysis On The Space-time Evolution Mechanism And Driving Of Eco-environment In Hai Lintu River Valley

Natural growth of vegetation is mainly influenced by the region's natural and human factors.The influence of natural factors on the natural difference and evolution of vegetation ecology in a region is relatively slow in a short time;While human activities,because of its subjectivity and uncertainty,the regional impact of vegetation change even more rapidly within a short time.The research area is located in the transitional zone of the Loess Plateau and Maowusu Desert in northern Shaanxi.In the region,the rainfall is scarce and the evaporation is strong,which is a typical semi-arid basin in the northwest of China.The process of ecological succession of local vegetation is restrained by the natural factors and human factors.Therefore,the distinction between natural factors and human factors in the process of changing the proportion of vegetation ecology can provide scientific basis for the protection and management of ecological environment in the region,which has important theoretical significance.The paper starts from the normalized difference vegetation index NDVI,using remote sensing techniques,calculating the surface evapotranspiration based on SEBS model,analyzing different natural factors affecting vegetation growth in Hailiutu River basin.Taking NPP as public indicator which distinguish the influence between natural and human factors in the vegetation ecotope evolution process,analyzing the natural and human driving force quantitatively.,supplying some scientific basis of regional ecological protection and governance for the government,which came to the following results through a large number of calculation and analysis:(1)Getting the spatial and temporal distribution of NDVI and Influencing factorin the research areaAdopting the MVC method to rebuild the NDVI data of MODIS 16,getting the monthly and yearly NDVI maximum,and Simulating to get the spatial and temporal distribution of NDVI with the average method?interpolation method and unitary linear regression.On the whole,in the time,the NDVI of the research area increased slowly from 2003 to 2014,and in the space,the NDVI is generally low in the research area.Through a correlation analysis of NDVI and which influencing factor of time and space differentiation,we found the climatic drivers of the time evolution and the influence factors of space differentiation.(2)Retrieving and estimating the fluxes and evapotranspiration in the research areaBased on the SEBS(Surface Energy Balance System)model,modifying the model parameters for the feature of naturel factors in the Hai Liutu River Basin,and using the NDVI data and surface temperature data of MODIS to estimate the surface albedo ? solar net radiation?soil heat flux and the sensible heat flux,and then calculating the daily evaporation of Hai Liutu River Basin with surface energy balance equation.Analyzing the spatial distribution of the fluxes and evapotranspiration,and discussing the correlation to NDVI through fitting analysis.(3)Revealing the spatial and temporal distribution of the actual NPP in research areaThe paper starting with the surface vegetation change resulted from the evolution of vegetation ecology,taking the Net Primary Production(NPP)as the index to measure the action of proportion of natural factors and the human factors in the process of vegetation ecological evolution.we build the CASA(Catnegie-Ames-Stanford Approach)model to estimate the actual NPP and the potential NPP,and using the slope value simulating to get the annual change trend of actual NPP in 2003-2012,finally revealed the spatial distribution of the actual NPP in the Hai Liutu River Basin.And it turned out that the method could objectively reflect the trend of change of NPP.(4)Quantitatively evaluating the action of natural factors and the human factors in the process of vegetation ecological evolution in the research areaUsing the actual NPP and the potential NPP to quantitatively analyze the action of proportion of natural factors and the human factors in the process of vegetation ecological evolution in the research area,which result showed that the proportion of climate factors was bidirectional,and contribution of the human activities to NPP growing gradually increased,while the climate factors gradually descended,which indicating that the human activities influence to the vegetation ecological in the study area gradually increased.