| Cities are the centers of economy, politics, science and technology, as well as culture and education, which play a leading role in the construction of socialist modernization in China. From a geographic point of view, urban areas are special geographical environments where human intervention on the natural environments is very intense. They are incomplete and fragile environmental systems where human are sensitively influenced by feedback from natural environments. They are also extremely complex giant systems in dynamic changes. The ultimate purpose of urban economic development is to enrich the people, improve the people’s living standards. Good ecological environment is a necessary condition for the high quality of life.Over the past decades, urbanization has taken place at an unprecedented rate around the world. In1950, as an example, only29%of the world population resided in urban areas, and this number rose to52%by2011. Moreover, this trend is projected to continue in the future decades. Since its reform and opening up in1978, China has also experienced a rapid urbanization as a developing country. The level of urbanization has increased greatly in China. Particularly, since approximately1990, there was a dramatic shift in urbanization in China. As a large number of people migrated to cities, the expanding population put unprecedented pressure on cities, particularly in built-up areas. Under this background, the urban extents expanded continuously. The total area of the built-up areas (municipalities, prefecture-level cities and county-level cities) were13148km2in1990and41755.7km2in2010in China. Urbanization promoted the rapid development of the urban economy. At the same time, rapid urbanization has led to a number of ecological and environmental problems (e.g. damage to vegetation, water quality degradation, air pollution, loss of biodiversity, and urban heat island effect). Urban vegetation is a very important part of the urban ecosystem, and has an irreplaceable importance in improving the urban ecological environment. Urban vegetation provides a good living environment for urban residents and a suitable habitat for urban creatures. Urban vegetation can give a more natural urban landscape and promote harmonious coexist between urban residents and nature environments. Urban heat island effects have changed urban heat environment and influenced regional climate, air quality in cities and distribution and behavior of urban creatures and consequently triggered a series of ecological and environmental problems. With the increasing requirement of improving urban residents’living environments, the issues of urban heat environments, as a comprehensive reflection of the city’s ecological environment, are getting more and more attention from urban residents. In particular, environmental changes within built-up areas were the strongest during the Chinese transition period. The construction of built-up areas not only directly impacts the quality of China’s urbanization, but also largely affects the process of sustainable development in China.There were many researches on the regional ecological environmental changes caused by urbanization, relatively few studies focused on the built-up areas. There is some research for a certain city or a type of cities, but, systematic, comprehensive, quantitative study on656built-up areas is relatively rare. This study summarized the relationship between urbanization and ecological environment, and proposed theoretical assumptions of the relationship between urban development and urban ecological environment, built the mechanism models how human factors impacted vegetation, the heat island effect in built-up areas. This paper selected the built-up areas in656cities, and analyzed vegetation and the heat island effect changes with urban development in build-up areas. Urban development included urban population, urban GDP and the expansion of built-up areas. From two aspects of vegetation and urban heat island, urban ecological environment was measured. Finally, the theoretical assumptions were verified. The main conclusions are as follows:(1) Relationship between urban development and urban ecological environmentWith the development of the city, the urban ecological environment first showed worsening trend. When the urban population (urban GDP or built-up area) reached a critical point, the urban ecological environment was improved with the urban development. During the same period, urban ecological environment was different in built-up areas with different scales. In the early and medium-term development periods, the larger cities of the urban population (urban GDP, the built-up area) was, and the worse urban ecological environment was. In the late development period, urban ecological environment turned good.(2) Expansion of built-up areasDuring the same period, the speed of urban spatial expansion increased with urban size. From1992to2010, the speed of urban spatial expansion was high in eastern China, low in central and western China, and the lowest in northeastern China. During the same year, the values of the compactness of urban external spatial morphology were getting smaller with increasing city, and were larger in central and western China than those in eastern and northeastern China. (3) Urban development and vegetation in built-up areasDuring the same period, the status of vegetation was different in built-up areas with different scales (urban population, GDP, or the built-up area). In1992and2000, with the increase of the urban population (urban GDP and the built-up area), vegetation became worse in built-up areas. In2010, with the increase of the urban population (urban GDP and the built-up area), vegetation first became worse and then became better in built-up areas.(4) Urban development and urban heat island effectIn1992,2000and2010, with the increase of the urban population, urban heat island effect became greater in built-up areas. But the increasing trend was reducing. In1992and2000, with the increase of urban GDP (the built-up area), urban heat island effect became greater in built-up areas. In2010, with the increase of urban GDP (the built-up area), urban heat island effect first became worse greater and then became less in built-up areas.(5) Human impacts on vegetation in built-up areasIn1992and2000, the negative impacts of human factors on vegetation were greater at larger urban scales in built-up areas. In2010, from the small cities, medium cities, large cities to mega-cities, the adverse effects of human factors first increased and then decreased. From1992to2010, the negative impacts of human factors on vegetation became less in metropolises and large cities, and it was almost unchanged in medium-sized cities and became greater in small cities. During1992-2010, the negative impacts of human factors on vegetation became less in eastern China, an increase was observed in central, western, northeastern China.(6) Human impacts on urban heat island effectThe larger urban scale was, the greater urban heat island effect was. The increase in urban scale promoted the urban heat island effect, but the promotion was reducing. The better urban vegetation (green rate and vegetation growth) was, the more it can alleviate, the urban heat island effect. Urban vegetation played a role to weaken urban heat island effect, and the alleviation was increasing. |
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