华北水利水电大学毕业设计
1.Introduction
Urban green spaces as an important contributor can be a significant part of sustainable development. Developments of urban green spaces need to consider interdisciplinary and integrative approaches such a economic, political, social, cultural, management and planning aspects to improve existing urban green spaces’ facilities and services, and to optimize urban green space policies. 2.1. Environmental Benefits 2.1.1. Ecological Benefits
Urban green spaces supply to cities with ecosystem services ranging from maintenance of biodiversity to the regulation of urban climate. Comparing with rural areas,differences in solar input, rainfall pattern and temperature are usual in urban areas. Solar radiation, air temperature, wind speed and relative humidity vary significantly due to the built environment in cities . Urban heat island effect is caused by the large areas of heat absorbing surfaces, in combination of high energy use in cities. Urban heat island effect can increase urban temperatures by 5?C . Therefore, adequate forest plantation, vegetation around urban dweller’s house, management of water bodies by authorities can help to mitigate the situation.
2.1.2. Pollution Control
Pollution in cities as a form of pollutants includes chemicals, particulate matter and biological materials, which occur in the form of solid particles, liquid droplets or gases. Air and noise pollution is common phenomenon in
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华北水利水电大学毕业设计
urban areas. The presence of many motor vehicles in urban areas produces noise and air pollutants such as carbon dioxide and carbon monoxide. Emissions from factories such as sulphur dioxide and nitrogen oxides are very toxic to both human beings and environment. The most affected by such detrimental contaminants are children, the elderly and people with respiratory problems .Urban greening can reduce air pollutants directly when dust and smoke particles are trapped by vegetation. Research has shown that in average, 85% of air pollution in a park can be filtered .
Noise pollution from traffic and other sources can bestressful and creates health problems for people in urban areas. The overall costs of noise have been estimated to be in the range of 0.2% - 2% of European Union gross domestic product . Urban green spaces in over crowded cities can largely reduce the levels of noise depending on their quantity, quality and the distance from the source of noise pollution. In the contemporary studies on urban green spaces consider the complex urban ecosystem, conservation of the urban green spaces to maintain natural ecological network for environmental sustainability in cities. For the cities in fast urbanizing and growing economy, country like China should consider the dynamic form of urban expanding to manage effective urban green spaces which will contribute to reduce the overall CO2 by maintaining or even increasing the ability of CO2 absorption via natural eco-system . 3. Challenges toward Management of Urban Green Spaces 3.1. Socio-Economic and Demographic Factors
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华北水利水电大学毕业设计
High urbanization and the high pace of social and economic development in Asia resulting from the increase of population in cities, lack of infrastructure, congested traffic, environmental degradation and a housing shortage are major issues faced by cities in Asia in their sustainable development . According to population experts, 62 percent of the world’ population will live in urban areas by the year 2020, while the Asia-Pacific Region will contain about 49 per cent of that urban population and will have contained a level of urbanization of 55 per cent . But it is also need to mention that growth of population has been slowed down in Asia-Pacific region.
The great threat to health and safety in cities comes from water and air pollution. Especially those who are poor and do not have adequate ventilation systems, air pollution is hazardous for them women and children because they expose regularly and waterborne diseases are found most commonly in low-income groups because of inadequate sanitation, drainage and solid waste collection services . Another most important challenge facing in Asia region due to over urbanization is the conversion of agricultural land and forest for urban uses and the development of infrastructure in urban areas. As a result, widespread removal of vegetation to support urban ecosystem, ground water overdraft and put additional pressure on nearby areas may be even more ecologically sensitive and may even increase the higher frequency of flooding in urban areas .
Cities cover 2% of land space worldwide but consume 75% of the
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华北水利水电大学毕业设计
resources . Exposing city dwellers to local biodiversity can also trigger interest in environmental issues, especially since people’s first encounter with the environment is often in one’s home city or town rather than in distant places . The lack of established and zoned green space is a factor of urban sprawl as people move to the edge of a city to be closer to the rural setting that feels like a healthier environment . To meet socio-economic, environmental, psychological needs of urban dwellers, there should develop some criterion based on the attitudes of perceived user to shape adequate uses of land and provide facilities within urban green spaces in cities . Planning authorities were advised to adopt a strategic approach and plan positively for providing green spaces. This was to provide strong protection for existing ones, resist new development op-portunities which might diminish recreational provision, ensure accessibility, and to provide good quality green spaces and recreational facilities . 3.2. Quantitative Aspects of Urban Green Spaces
Understanding relationship between the urban population and the amount of green spaces is particularly important in evaluating their functionality, and of course future planning for their provision. Commonly used terms to refer to the quantity of green spaces are green space ratio, green space coverage and green space area per capita . It is very difficult to measure the appropriate amount of required land and allocation of land and calculate distance from residential area and especially to implement the measurement on building up urban green spaces with proper services in the highly populated countries. Table 1 shows the
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华北水利水电大学毕业设计
standards of minimum sizes of various types of green spaces in urban areas .
A study on 26 cities from 15 European countries considers four groups of the 26 cities, according to their population size, such as Metropolis, Big Cities, Medium-Sized Cities and Small Cities . To understand the availability of urban green spaces in Europe, the study conducts factor analysis by considering the factors“mixed land use” (such as residential areas, industrial areas, forest and agricultural areas); “man-made environment” (such as built-up area and urban green areas); and water . And the study finds that metropolis has a high score on man-made environment which includes built-up area and urban green . Considering the four groups of variables such as urban green areas, forests, agricultural areas and water, another factor analysis shows the two categories of cities included in the study“Natural Green Areas” (N) (such as forest and agricultural areas) and “Urban Green Areas” (U) ( such as urban green and water). Finally, the study concludes that the metropolis and the big cities have a high score on the urban green factor [2]. Because the cities are old, the cities have a high population density and the cities have a loss of natural areas and natural resources. In addition, medium-sized cities have a relatively high score on the natural green factor due to the availability of natural green areas .
However,
the study suggests investing more in urban green spaces in
metropolis cities and less invest in urban green spaces in medium-sized cities . But it is important to preserve the green areas either urban green or natural green. To confirm the conservation and to improve the better quality of urban green
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