Urban Land Expansion In China And Its Effect On The Major Environmental Factors

Urbanization in China becomes especially active since entering the 21^st Century,involving the multiple development of social-economy,science,technology,population and land,driven by the four Five-year Plans.As the most intuitive manifestation of urbanization,urban land in China is expanding dramatically,however,which inevitably brings numerous ecological problems.Against this background,this doctoral thesis is entitled"Urban land expansion in China and its impacts on the major environmental factors".The target is to supplement materials about China's urban land expansion and environmental change,as well as provide a scientific reference for China's urban planning.Urban land expansion is one of the major kinds of land resources transferation and greatly impacts on the structure of land use.In this paper,the urban land expansion in China and its impact on other land resources was systematically analyzed based on the National Land Use Database in China(NLCD-C)at multi-scales.Results show that(1)urban land in China grew from 32287.41 km²in 2000 to 67615.61 km²in 2015,with a 1.09-fold increase.(2)The cropland is the primary source of newly grown urban land(NGUL)with a contribution rate of 67.09%,followed by the rural settlements and industrial/transportation construction land(19.80%).Other 13.11%of newly grown urban land was mainly from woodland,grassland,water area and unused land.(3)The land resources were occupied by urban expansion unevenly from space,i.e.,cropland was occupied most seriously in the North China Plain,woodland near the middle and lower reaches of the Yangtze River,grasslands along China's agricultural-pastoral overlapping zones,water area close to the southeast coastals,and unused land in the northwest inland.Given the availability of data sets,the consistency of monitoring phase,as well as the independency and representativeness of indicators,three major fators were selected to investigate the impact of Chinese urban expansion on natural environment,i.e.,vegetation coverage(VC),land surface temperature(LST)and air quality(AQ).The data sets were from the MODIS products from the National Aeronautics and Space Administration(NASA)and particulate matter(PM)2.5 products from the atmospheric composition analysis team of Dalhousie University.Three statistical units were considered,including the entire administrative unit(EAU),the original urban land(EUL)in 2000 and the NGUL.Meantime,the impact of urban land expansion on environment was further analyzed by dividing China into rapid and slow expansion areas,identifying the expansion modes of urban land in China,as well as characterizing the spatial aggrelation of land resources conversation into urban land.Results show that(1)the expansion of urban land leads to rare influence on natural environment of wide ranges.In times of rapid urban expansion in China,the VC increased nearly 1.67percentages,the PM2.5 decreased 3.27?g/m³,and the LST showed just 0.68?increase.Of the total monitoring area in China,73.33%was seen VC increase trend,55.14%suffered LST increase trend,and 48.43%showed PM2.5 decrease trend.Similar phenomena could be seen in four economic zones,province and city scales.(2)The expansion of urban land brings relatively significant invluences on the local environment.Within the OUL,where carrying denser population and human activities,the VC increased by 0.81 percentages slightly,the LST increased by 0.89?,and PM2.5concentration was 23.22?31.19?g/m³ higher than the EAU.The changes in the NGUL were more distinct,i.e.,the VC decreased by 2.99 percentages,LST increased by 1.81?and PM2.5 concentrations of 22.21?31.97?g/m³ higher than the EAU.(3)In the rapid expansion zone,cities adopting accelerate urban land expansion modes or where cropland and other built-up land was occupied heavily by urban land expansion,the natural environment was more distinctly influenced,evidenced by more serious vegetation degradation,urban heat and air quality decrease.There are three innovation points in this study.(1)This study built a research framework investigating urban land expansion and its impact on major environmental factors,and comprehensively conducted the experiment at multi-scales in China.The results showed the basic characteristics of urban land expansion in China,its occupation on other land resources and the dynamic of three natural environmental factors.(2)This study built conceptual models of urban land expansion in China,and identified Chinese cities into four categories of“concave”,“convex-concave”,“concave-convex”and“convex”.The result revealed that megacities mostly expanded by“convex”mode,while other cities mostly by accelerating urban land expansion modes.(3)This study proposed the method for identifying the dynamic pattern of VC in times of urban land expansion.By which,Chinese cities was categoried into five forms.The new finding is that over 4/5 cities experienced significant VC increase,indicating the efficiency of a series of greening policies.Cities those suffered relatively serious VC decrease are mainly located in the fragile areas.Meantime,different dynamics of the LST and PM2.5were monitored and compared with three statistical units.The results showed the necessarity of monitoring urban land expansion in China and its impact on major environmental factors.