Research On Urban Expansion And Its Impact On Ecological Environment Quality In The Loess Plateau

As the most intuitive form of spatial expression of urbanization,urban expansion is an inevitable product accompanied by the continuous improvement of urbanization level,which marks the progress of human society.As a bridge connecting the east and west of China,the Loess Plateau is the main area of the national ecological security pattern and the implementation of high-quality development of the Yellow River Basin.Since 2000,the rapid urban expansion in this region has promoted the social and economic development on the one hand,but also caused the destruction of vegetation,air pollution and other ecological environment.Therefore,clarifying the law of urban expansion,the dynamic evolution of ecological environment quality and the impact of urban expansion on ecological environment quality in this region can provide scientific reference for sustainable urban development in ecologically fragile areas.Based on DMSP/OLS(Defense Meteorological Satellite Program,Operational Linescan System)and NPP/VIIRS(National Polar-orbiting Partnership,Visible Infrared Imaging Radiometer Suite)nighttime light remote sensing data,Moderate resolution Imaging Spectroradiometer(MODIS)surface reflectance data products and provincial and municipal statistical yearbooks,a long time series of night light data and Remote Sensing Ecological Index(RSEI)data of the Loess Plateau from 2000 to 2019 were constructed.On this basis,urban built-up areas were extracted and their accuracy was evaluated.Then,combined with Sen trend,standard deviation ellipse geographic detector and other research methods,the dynamic law of urban expansion,temporal and spatial evolution of ecological environment quality and the impact of urban expansion on ecological environment quality were discussed and analyzed.The main conclusions are as follows:(1)By comparing the dynamic threshold dichotomy model with the Otsu algorithm,it is found that the urban built-up area extracted by the Otsu algorithm is not easy to distinguish the edge of the built-up area,and the range of built-up area extracted by the dynamic threshold dichotomy model is more in line with the reality.From the perspective of accuracy evaluation,the accuracy of built-up area extracted by dynamic threshold dichotomy is high,and the overall error rate is only 5.60%.(2)Although the urban nighttime light intensity on the Loess Plateau showed a pattern of higher in the east and lower in the west from 2000 to 2019,the degree of spatial autocorrelation decreased with the time,the number of high-cluster and hot-spot cities gradually decreased,and the difference between cities gradually decreased.From the perspective of the distribution pattern and dynamic characteristics of urban expansion,the cities in the whole Loess Plateau gradually expanded to the southeast direction,and the expansion trend was relatively concentrated.The speed and intensity of urban expansion of most cities increased first and then decreased.The volatility of urban expansion decreased year by year,and the urban development tended to be stable.(3)The RSEI of the Loess Plateau showed an obvious trend of increase,among which 25.37% showed a significant trend of increase,mainly concentrated in the central region of the Loess Plateau,and 19.43% showed a significant trend of degradation,mainly concentrated in the Ordos Plateau and Guanzhong plain.From the perspective of spatial distribution of ecological grade of RSEI,the spatial pattern of RSEI decreased from southeast to northwest.The regions with higher RSEI were mainly distributed in the region of Qinling,which located in the southeast of the Loess Plateau,while the regions with lower RSEI were mainly concentrated in the Mu Us desert in the northwest of the Loess Plateau.From the perspective of evolution,the area of lower RSEI decreased significantly,indicating that the eco-environmental quality of the Loess Plateau was significantly improved.The driving force analysis shows that land use change has an important impact on ecological environment in terms of human controllable factors.(4)The core area and the near urban area both have different degrees of decline in eco-environmental quality,among which the near urban area has the most serious decline.In the area of urban expansion,the impact of urban expansion on ecological environment fluctuates in different stages.From 2000 to 2005,urban expansion on the Loess Plateau had the most serious impact on ecological environment,while from 2010 to 2015,urban expansion on the Loess Plateau had the least impact.From the perspective of space,the impact of urban expansion on ecological environment is two-sided.Ecoenvironment quality in the area accounting for 10.52%,mainly distributed in the core cities,was on the decline with the urban expansion,while 5.50% of regional urban expansion promotes obvious improvement of ecological environment quality,mainly distributed in the central region of the Loess Plateau.