Study On Spatiotemporal Evolution And Influencing Factors Of Urban Expansion In Yunnan Province Based On NPP/VIIR

With the rapid development of our economy,the urbanization process of various areas is also being accelerated,but it can cause a series of urban problems and natural environment problems.Urban built-up area is an important indicator to measure the level of urbanization,and its changing state can also reflect the future development direction of the city in a certain period of time.Therefore,through the dynamic monitoring analysis of urban built-up area expansion and the study of influencing factors,it can provide certain reference significance for the rational layout of urban development and the influencing factors of urbanization development.Taking Yunnan Province as the research region,this paper extracted the urban built-up areas of 16 cities and prefectures in Yunnan province by using the NPP/VIIRS night light data in 2013,2015,2017 and 2019,and analyzed the extracted built-up areas from two aspects of temporal characteristics and spatial characteristics changes through multiple indicators.Finally,combined with the social and economic data,the paper quantitatively analyzes the economic,social and population factors affecting the urban built-up area expansion in Yunnan province.The main conclusions of this paper are as follows:（1）Statistical data comparison method,vegetation modified light index method and PELANUI index method were used to extract the urban built-up area,and the accuracy of the three methods was compared and analyzed.The results show that PELANUI index method has a high precision in the extraction of urban built-up area,and the deviation from the statistical data is 0.17%.The extraction accuracy reached84.7%,and the extraction results can be used to analyze the urban built-up area expansion change in Yunnan Province.（2）Based on the PELANUI index method,the urban built-up area of Yunnan Province was extracted,and the change of urban built-up area expansion was analyzed from two aspects of time series and spatial characteristics.The characteristics of time series are analyzed from the change of urban built-up area,urban expansion rate and expansion intensity.In yunnan province,the overall growth area,expansion rate and expansion intensity changes are first drop after rising trend,in 2013-2015 as the maximum,118.75km²,59.375km²?a^-1and 0.01525%;During the study period,the built-up areas of Qujing City and Kunming City increased more,while those of Diqing City and Lijiang City increased least.In the analysis of expansion rate,Kunming City and Qujing City expanded faster,while Diqing Prefecture expanded the slowest,showing a state of gradual growth.The expansion intensity of each city and state also showed different changes,among which Xishuangbanna changed rapidly,gradually developing from the most backward level to the leading level.The spatial characteristics were explored by compactness index,fractal dimension,shift and change of center of gravity,expansion orientation and other indicators.The compactness index of Yunnan Province decreased slightly on the whole,and the whole built-up area tended to diverge.During this period,the built-up area of Diqing Prefecture,Lijiang City and Xishuangbanna was relatively compact,while that of Kunming City,Zhaotong City and Honghe Prefecture was relatively dispersed.The overall fractal dimension of Yunnan Province is more than 1.7,indicating that the overall urban built-up area of Yunnan Province is more complex,and the fractal dimension of each city and prefecture presents different characteristics.From the perspective of barycenter migration changes,the whole barycenter of Yunnan Province distributes in the southeast of Chuxiong Prefecture and gradually migrates to the northwest in the past 6 years.The distance and direction of barycenter migration are different among cities and prefectures.Baoshan City has the furthest distance of barycenter migration,Kunming City has the shortest distance of barycenter migration,and the most direction of barycenter migration is southeast direction,while the least direction of barycenter migration is northeast direction.The expansion direction of built-up area of each city and state has different changing characteristics,and most cities and states mainly expand to the direction of more developed cities and states.（3）The spatio-temporal geographical weighted regression model was used to study the spatio-temporal evolution of built-up area and driving factors in cities and prefectures of Yunnan Province.The results show that the influence of different factors on the built-up area of different cities and states presents the alienation effect of business trip.The regression coefficients of six driving factors,namely the proportion of the primary industry,the proportion of the tertiary industry,fiscal expenditure,fixed assets investment,urban population and total social consumer goods,are different in the same stage but in different cities and states,and in the same city and state but in different stages.All driving factors show the effect of business alienation.The total amount of consumer goods and urban population are important factors to promote the growth of urban built-up areas in Yunnan Province.