Research On Spatio-Temporal Variations In Vegetation Net Primary Productivity And Their Impact Factors In Yellow River Basin Based On Muti-Source Data

In recent years,with the rapid development of science and technology and the rapid development of modern industry,human beings have become more and more prominent in the transformation of nature,especially in environmentally vulnerable areas.Under the influence of climate change and human activities,the Yellow River Basin has intensified soil erosion and the vegetation ecosystem is degraded.The net primary productivity of the vegetation ecosystem is not only a key factor in assessing carbon balance,but also an important indicator for measuring vegetation quality and evaluating ecosystem structure and function.Therefore,it has important practical significance to study the temporal and spatial variation of vegetation NPP and its influencing factors in the Yellow River Basin.This paper uses the 2000-2015 MOD17A3 dataset to analyze the temporal and spatial characteristics and trends of vegetation NPP in the Yellow River Basin.At the same time,the correlation between MOD17A3 NPP and climatic factors?temperature,precipitation?,land use/cover type,topography?height,slope,aspect?and soil type were studied.And by exploring the pixel characteristics and R² of the 2000MOD17A3 NPP and GLOPEM NPP data,the two data were combined to obtain the spatial-temporal variation of vegetation NPP in the Yellow River Basin from 1986 to2015,and the long-term sequence remote sensing monitoring of vegetation NPP in the Yellow River Basin was realized.The main conclusions drawn are:?1?The mean annual NPP of vegetation in the Yellow River basin from 2000 to2015 was 228.2gC·m^-2·a^-1,and the variation range was 179.6-258.1gC·m^-2·a^-1.On the whole,the NPP of vegetation increased slightly,and the deviation of vegetation NPP decreased first and then increased.The vegetation NPP in the Yellow River basin has strong spatial variability and presents a decreasing distribution from south to north.The change trend of NPP in the Yellow River basin is significantly different in regional space.According to the proportion of the change rate of NPP,the increase of NPP is the main trend in most areas of the basin.The middle and upper reaches of the basin contribute the most to the vegetation NPP of the whole basin and have a significant impact on the ecological environment of the whole basin.Therefore,it is of great importance to strengthen the ecological environment construction and protection of the middle and upper reaches of the basin.?2?The vegetation NPP in the Yellow River basin is mainly affected by precipitation in qilian mountain,tengger desert,liupan mountain,maowusu sandy land,ordos plateau,western sichuan plateau and parts of the north China plain.The areas mainly affected by temperature include western sichuan plateau and parts of the north China plain.Regions driven by climate factors account for 23.91%of the Yellow River basin,and regions driven by non-climate factors account for 76.09%,indicating that with the acceleration of urbanization,human activities are gradually becoming the main driving force affecting the change of vegetation NPP.In the Yellow River basin,the sensitivity of vegetation NPP to temperature first decreased and then increased from the west to the east,and the sensitivity to precipitation decreased from the north to the south.The contribution of all meteorological factors from the northwest to the southeast of the Yellow River basin to NPP decreased gradually,which was consistent with the spatial distribution of the relative changes of NPP in the Yellow River basin over the years.?3?The land use/cover types in the Yellow River Basin are mainly characterized by construction land,agricultural land,forest land transfer,and conversion of grassland,water area and desert.The conversion of agricultural land to construction land and grassland to desert is the main way of NPP loss in the Yellow River Basin.Accelerated expansion and human activities such as excessive reclamation and grazing are the main driving forces for vegetation NPP loss.In recent years,the area of forest land and grassland has increased,and the overall loss of vegetation NPP has decreased.It can be seen that ecological deterioration and environmental vulnerability are recognized.After serious problems,the implementation of the policy of returning farmland to forests and grasslands has yielded results.Among the regional environmental factors,different levels of altitude,slope,and slope direction cause different amplitudes of NPP changes,and different directions;different types of soil have different effects on the interannual variation trend of vegetation NPP,and the vegetation NPP of most soils increases.Only the alluvial soil showed a decreasing trend,indicating that the alluvial soil has not been completely separated from the influence of river flooding.?4?The common point of both MOD17A3 NPP and GLOPEM NPP data is that both can reflect the decreasing trend of vegetation NPP in the Yellow River basin from south to north,and the east is higher than the west.The difference is that the value of GLOPEM NPP is generally higher than that of MOD17A3 NPP,and the average value of GLOPEM NPP is 3.1 times higher than that of MOD17A3 NPP.The linear regression equation y=1.3287x+345.72,which has high feasibility and relatively small deviation from the true value,was used as the fusion formula for MOD17A3 NPP and GLOPEM NPP.The fusion results showed that the maximum value of NPP in the Yellow River basin decreased over the past 30 years from 1986 to2015,the annual mean value increased slightly on the basis of maintaining stability,and the average annual vegetation NPP in the Yellow River basin decreased from south to north as a whole.