Spatial-temporal Assessment Of Urban Expansion Impactson Ecosystem Services In Chongqing City

The disorderly expansion of urban land leads to the decline of ecosystem service function,which affects the coordinated development of society,economy and ecology.Based on DMSP/OLS data and Landsat TM/OLS data in 2005 and 2015,this paper analyzed the characteristics of urban expansion from three aspects(time,space and process)using methods of DN value classification,maximum likelihood,sector statistical analysis,buffer analysis and public edge measurement.Meanwhile,Based on MODIS 250 meters per 16 day composite NDVI data and crop yield data,the spatial distribution and changes of food supply in 2005 and 2015 were simulated using food supply model;Based on land use data,MODIS 250 meters per 16 day composite NDVI data,meteorological data(monthly mean temperature,monthly total precipitation,monthly total solar radiation),the spatial distribution and changes of NPP in 2005 and 2015 were simulated using CASA model;Based on land use data,soil type data and daily precipitation data,the spatial distribution and changes of runoff depth in 2005 and 2015 were simulated using SCS_CN model.Finally,through correlation analysis and normalization analysis,the changes of ecosystem services and trade-off or synergy are explained in different urbanization categories,discussed the problems and challenges in process of urban expansion,and gives some ideas for future urban development.The basic conclusions are as follows:⑴ The Chongqing city was separated into three urbanization categories(developing urban,developed urban,and rural areas),and analyzed the characteristics of urban land expansion from perspective of time,space and process.In terms of time,urban land has expanded dramatically,from 2005 to 2015 increased by 373.9km.In terms of space,the urban land expansion was the smallest because of urban land distribution in developed areas was relatively saturated,development urban was the largest,urban land extends along the northeast and southwest directions,Yubei District and jiangbei District in the east-northeast direction were affected by the "liangjiang new area",and the increment of urban land was the largest.In terms of process,the expansion form of urban land changes with the distance from the city center,on the whole,it is dominated by edge-expansion and supplemented by leapfrog expansion.⑵ Spatial-temporal distribution and changes of ecosystem service functions: In 2005 and 2015,the service functions of food supply,carbon sequestration and soil water storage were the lowest in developed urban areas,followed by development urban areas,and the highest in rural areas.In addition,the ecosystem service functions have showed tendency of significant decline,the largest decline area was development urban,which coincided spatially with the area with the greatest urban expansion,it showed that the change of land use type caused by urban expansion was an important reason for the decline of ecosystem service function.⑶ The trade-off and synergy between ecosystem services were affected by the degree of urban development: The relationship between food supply and NPP was trade-off in 2005,but only existed trade-off relationship in rural areas in 2015.In 2005 and 2015,the relationship between food supply and runoff depth was trade-off in developed urban and developing urban,in rural areas was synergy.⑷ Urban expansion has significant impacts on ecosystem services: The urban expansion leads to the decline of ecosystem services,the change coefficients of food supply,NPP and runoff depth in developed urban were-0.3,0 and-0.05,respectively;the change coefficients of food supply,NPP and runoff depth in the developing urban were-0.41,0.1 and-0.1,respectively;the change coefficients of food supply,NPP and runoff depth in the rural areas were-0.15,0.02 and-0.1,respectively.the areas with biggest decline of ecosystem service was developing urban,and food supply was the most obvious service function of the recession among ecosystem services.⑸ It was found that the rapid expansion of urban land destroys the ecosystem services,reduces the environmental capacity and affects the comfort of residence of citizens.Meanwhile,the housing price in city was so high that many residents have not realized true urbanization,the quality of urbanization was not high.In view of this,developed urban areas should increase infrastructure construction,the aggressive land expansion in developing urban areas should be controlled,rural areas continue to strengthen ecological regulation functions.In addition to improving the ecological environment,the psychological pressures of citizens,such as the excessively high housing price,should also be addressed,and promote a new type of urbanization with people at the core.The research results of this paper provide a scientific basis for analyzing the causes of the problems in the urbanization process,seeking the coordinated development,and Rational planning and development in Chongqing city.