Study On Dynamic Change Of NPP And Grassland Change In Northern Tibet Based On Remote Sensing And Biological Processes Model BEPS

Land-use/Land-cover change and terrestrial carbon cycle are the current international researchhotspots on global change research area. In this paper, based on two land-use /land cover images forthe year 1990 and 2000, the change of grassland degradation and unused land in Nakchu areanalyzed. The reasons of these changes are analyzed using the meteorological data and populationstatistic. The temporal and spatial variations of NPP are analyzed using NOAA NDVI data and NPPprocess model.The main progresses that this research has made are summarized as follow:1) Land-use/Land-cover change:It is not remarkable that LUCC in Nakchu from 1990 to 2000,but the dynamic transit between different land use is very complex, especially the transit between thegrassland and unused land. The results show that the unused land in Nakchu was increased and thegrassland was decreased from 1990 to 2000. The primary changes were that grassland was convertedinto unused land, forest and ploughland. The cause of resulting in these outcomes is mainly impactsof human economic activities on eco-environment. The impacts of human economic activities onland use change in Naqu are more intensive than the impacts of natural facts.2) The dynamic change of NDVI: spatial distribution and dynamic change of vegetation coverin Nakchu were studied using NOAA AVHRR-NDVI data from 1981 to 2001. The map of NDVIlinear trend showed the spatial and relative changes of NDVI in each pixel by means of GIS.Vegetation cover of the research area displayed by NDVI tends to be high in the east-south of thearea and low in the west-north , and agriculture and forestry area > alpine meadow > alpinegrassland > desert grassland;In the research area , the area of high increase , slight increase , nochange , slight decrease and high decrease are 0.27 %,8.71 %,77.27 %,13.06 % and 0.69 % of thewhole region. The increase and high decrease of vegetation cover pixels distribute in the alpinemeadow , light decrease pixels distribute in the alpine grassland and desert grassland;In the areawhere human being live , the trend of change is obvious , human being's behaviors is a key factorfollowed by the climate changes affecting vegetation coverage.3)Interannual variation and the spatial change of NPP simulated by BEPS model:.According toa carbon-water coupled process model driven by remote sensed data and climatic data ,meangrassland NPP in Nakchu were 62.4gC/m2·a , the change of NPP ranged from 0 gC/m2·a to 151.7gC/m2·a .The NPP of alpine meadow NPP is more than 110gC/m2·a,then alpine grassland rangedfrom 0 gC/m2·a to 50gC/m2·a,desert grassland is less than 50gC/m2·a.According to modelsimulations, the grassland NPP have different sensitivities to various environmental factors(LAI,temperature and precipitation). NPP is positive related to precipitation and LAI;the relation betweenNPP and temperature is complex.