| With China's urbanization entering a period of accelerated development,how to effectively and rationally assess the relationship between urban expansion and landscape ecological risk levels in the process of urban expansion,to reduce ecological risks,to protect the ecological environment and achieve sustainable social-economic development is particularly important.Taking Nanchang City as an example,this thesis used urban expansion intensity index and expansion speed to study the spatial and temporal variation characteristics of urban spatial expansion from 2000 to 2017 by using remote sensing,GIS and mathematical statistics methods.System sampling was carried out with a 3 km×3 km cell grid to explore the dynamic changes of landscape pattern and landscape ecological risk in Nanchang City under urban expansion.The CA-Markov model was used to predict urban expansion from 2025 to 2030 and the dynamic changes of landscape pattern were analyzed.Based on the geographically weighted regression model,the coupling relationship between urban spatial expansion and landscape ecological risk in Nanchang City from 2000 to 2017 and from 2025 to 2030 was analyzed from the aspects of urban land area and landscape ecological risk value,urban expansion intensity index and landscape ecological risk change value.I hope it could promote the coordination between urban construction and ecological environmental protection,correctly evaluate the influence of urban spatial expansion on urban ecosystem,and provide references for the sustainable development and scientific management of Nanchang City.The conclusions were as follows:(1)From 2000 to 2017,the urban land area of Nanchang increased from 107.87 km~2to 355.43 km~2,among which the fastest expansion was in 2000-2005,with an average annual expansion rate of 39.62 km~2/a.During the study period,the compactness of urban land use in Nanchang was poor and the urban expansion was mainly external expansion.The expansion of urban land showed some differentiation characteristics.The northwest and north areas expanded rapidly,and the east,southeast,and northeast regions expanded slowly.The area with rapid expansion was mainly in the downtown area of Nanchang,where the terrain was flat.The urban land in Qingshan Lake District,Nanchang County and Xinjian District expanded rapidly,while the east,southeast and northeast regions were hindered by Junshan Lake,Qinglan Lake and topography and the spatial expansion of urban land was relatively small.(2)From 2000 to 2017,the construction land in Nanchang City expanded rapidly,the area of cultivated land,forest land and grassland decreased continuously,the number of landscape patches increased,and the overall fragmentation degree increased.The average value of ecological risk of landscape increased from 0.135 4 to 0.142 0,and the risk value increased gradually.The distribution of ecological risks was dominated by low ecological risks and lower ecological risks.The area of these areas reached more than 50%.The medium ecological risks were mainly distributed in the West Lake District in the central part of Nanchang City,the eastern part of Qingshan Lake District,and the northeastern part of Nanchang County.The higher ecological risk and high ecological risk were relatively small in the whole research area,which were mainly in the waters with higher vulnerability and unused land.The anti-interference ability of ecosystem was low,so landscape ecological risk was high.From 2000 to 2017,the coupling analysis of urban land area and landscape ecological risk,as well as urban spatial expansion intensity index and landscape ecological risk change value in Nanchang City showed that there was a negative correlation between them,but the correlation between the latter was weakening.From the spatial distribution of the regression coefficient,the low values were distributed in the areas with rapid economic development such as Donghu District,Xihu District and Qingyun Spectrum District,while the high values were distributed in areas where urban land expansion was relatively slow such as Jinxian County and Anyi County.(3)Using the CA-Markov model,the urban land area of Nanchang City in 2025 and2030 is 370.23 km~2 and 376.57 km~2 respectively.In the future,urban spatial expansion will expand along the main urban area to the surrounding areas,and the actual urban land area of each region will increase in trend,and urban spatial expansion will be relatively fast.From 2017 to 2030,apart from urban land,the number of different landscape patches in Nanchang City has been decreasing,the overall fragmentation decreased from 1.3546 to0.6245,the area of cultivated land and unused land has been decreasing,and the area of urban land and other construction land has been decreasing.The area of waters and woodland is also increasing due to the implementation of relevant protection measures.The average value of landscape ecological risk will decrease from 0.141 1 to 0.093 0,and the risk value show a rapid downward trend.The area of low ecological risk area increases significantly,the medium ecological risk area is transformed into low and low ecological risk area,and the area of high ecological risk zone and higher ecological risk zone are reduced,and the city is developing in a more orderly direction.The urban land area and the landscape ecological risk also show a negative correlation on the whole.On the spatial distribution of regression coefficients,the positive values appear in Nanchang County and Xinjian District,which have developed rapidly,and the negative values distribution range is large.During the three periods from 2017 to 2030,the coupling relationship between urban expansion intensity index and landscape ecological risk change is weak.The distribution of regression coefficients has positive or negative values,and the positive values are also distributed in the fast-growing Xinjian District,Nanchang County and Qingshan Lake District,while the negative values are distributed in Jinxian County,Donghu District and Xihu District.In general,the coupling relationship between them is weak.(4)Nanchang City had a series of problems in the process of urban space expansion.In the future,we should strengthen the optimal allocation of urban land,rationally layout the urban spatial structure,and guide the healthy development of the city.We must strengthen the management of landscape ecological risks in the process of urban spatial expansion,formulate scientific and rational development policies,and achieve sustainable development of regional economy and society. |
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