| With the continuous promotion of urban development,there are significant dynamic changes in urban space.As an important component of urban space,built-up area is also an important form of urban space evolution,which shows the trend of rapid growth in quantity and scale in the process of urbanization.As an important indicator of carbon cycle,net primary productivity of vegetation can reflect the production capacity of regional vegetation community and the quality of terrestrial ecosystem.However,the expansion of built-up area has a great impact on the change track of NPP.Studying the changes of built-up areas caused by human activities and their impacts on vegetation NPP on a global or regional scale is not only conducive to deepening the understanding of global carbon cycle and its regulation mechanism,but also of great significance to urban land use and regional ecological planning.In this study,the Three Gorges Reservoir area is located in the area under the jurisdiction of Chongqing Municipality?i.e.Chongqing section of the Three Gorges Reservoir Area?.Based on the night lighting data of 2000-2015 and Chongqing statistical yearbook,the built-up area is extracted.ArcGIS software and various indexes have analyzed the expansion characteristics of the built-up areas,and the Chongqing section of the Three Gorges Reservoir Area 2000-2015 is analyzed by mod17a3 data The spatial-temporal distribution and change characteristics of NPP in the study area were analyzed,and the influence of the change of the scale and degree of the built-up area on NPP was discussed.It comes to the results:?1?Based on the NPP/VIIRS data of 2013,it is fitted with the DMSP/OLS Data of the corresponding year,and the DMSP/OLS Data of the corresponding period is obtained through the obtained simulation equation.Through the analysis of spatial distribution,correlation and standard deviation of each pixel data,it is considered that the simulation effect is good,and the integration method is feasible,and the continuous night light from 2000 to 2015 is obtained Data set.?2?From 2000 to 2015,the built-up area of the kuwei district is in the north,while the built-up area of the kuwei district is mainly in the north northeast and south southwest;the center of gravity of the built-up area is mainly distributed in the Yubei District,indicating that the development direction of the built-up area is gradually moving northward;the compactness index of the study area is less than 0.1,showing a trend of first decreasing,then increasing,then decreasing,and then showing a trend of"dispersion aggregation dispersion"”The fractal dimension of urban boundary fluctuates greatly from 2000 to 2003,increasing first and then decreasing.From 2003to 2013,the fractal dimension of built-up area expansion is relatively stable.In 2014and 2015,the built-up area expansion shows obvious external extended development.?3?Combined with the analysis of elevation,the built-up area is mainly distributed in hilly areas,with the area proportion floating in the range of 78%-83%,closely followed by plain areas,and then low-mountain areas,with the area proportion of about15%and 5%,respectively.From the angle of slope,it is mainly distributed in slope area,with the average area accounting for about 43%,steep slope area and gentle slope area accounting for more than 20%,followed by steep slope area,which accounts for the smallest proportion,with the area accounting for less than 1%.As a mountainous area,the proportion of plain to slightly inclined plain in the whole study area is very small,only about 3.5%,but the proportion in the built-up area has increased to more than 7%,the highest is 9.61%.?4?The annual mean NPP of vegetation in the study area fluctuated between481.512-658.557 gC·m-2·a-1,from the year 2000 to 2015,and the overall level of NPP of vegetation was good,but there were differences in its spatial and temporal distribution,and the NPP of vegetation in the northwest was significantly lower than that in the southeast;boundaries by the Yangtze River Basin,the NPP of vegetation in the North was lower than that in the South where were significantly different from the North.NPP of vegetation per unit area in the built-up area is obviously smaller than the average value of the whole study area,but the total NPP of vegetation in the built-up area is still on the rise,and by the time the proportion of zero value is gradually reduced.From the difference and change rate of NPP of vegetation in 2000 and 2015,it can be seen that the positive change is greater than the grid number of negative change,and the larger the change range is,the smaller the proportion of grid number is;NPP of vegetation appears clearly The areas with significant negative growth are mainly concentrated in the built-up area,while the areas with significant positive growth are found in Yunyang County and Kaixian County in the northeast of Chongqing.The grid with slow change range is scattered and the spatial law is not strong.?5?Nighttime lighting data also implys that it can be well explained that with the continuous expansion of the built-up area,although the area of the built-up area is increasing,the development degree of the new built-up area is much smaller than that of the old built-up area,which is also an important reason for the annual increase of NPP in the built-up area in 2000,2005,2010 and 2015.?6?From the perspective of land-use transformation in the built-up area,the average distribution of NPP in Chongqing section of the Three Gorges Reservoir area is grassland>cultivated land>forest land>unused land>construction land>water area.The decrease of NPP in the built-up area is caused by the land-use transformation in the built-up area to some extent,especially the significant change of a large number of cultivated land into construction land to the net primary productivity of vegetation in this area Negative impact.From 2000 to 2015,both the information entropy elastic coefficient and the comprehensive change elastic coefficient of land use structure were negative,which indicated that the NPP of land use change to the vegetation in the built-up area of Chongqing section of the Three Gorges Reservoir area was restrained from2000 to 2015. |
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