J. Cent. South Univ. Technol. (2011) 18: 101-107

DOI: 10.1007/s11771-011-0666-x

Exploring harmonious development between urbanization and eco-environment based on climate analysis—A study in Changsha, China

LIU Shao-bo(刘少博)¹, WEI Chun-yu(魏春雨)¹, GUO Ya-qi(郭亚琦)², ZENG Xiao-xia(曾晓霞)²,

LIU Su(柳肃)¹, YIN Yi-chen(尹怡诚)¹, LIU Yun-guo(刘云国)²

1. College of Architecture, Hunan University, Changsha 410082, China;

2. College of Environmental Science and Engineering, Hunan University, Changsha 410082, China

? Central South University Press and Springer-Verlag Berlin Heidelberg 2011

Key words:

urbanization; urban warming; eco-environment effects; harmonious development; Changsha；

1 Introduction

Rapid urbanization can be observed in China. According to the official report, the urbanization level of China has increased from 22% in 1983 to 44.9% in 2008 [1]. It is well known that the urbanization has many deleterious environmental effects [2], and it also affects the climate. Firstly, natural ecosystems are increasingly replaced by sprawl of urban fringe, and therefore less heat reflected by lower-albedo surface directly makes the world become warm. Secondly, increased levels of atmospheric carbon dioxide and other greenhouse gases (i.e. methane, nitrous oxide, chlorofluorocarbons, tropospheric ozone, and stratospheric water vapor) are thought to contribute to an increase in atmospheric temperatures [3]. Thirdly, the increase of population size implies more human activities related to the urban warming.

There is a clear relationship between urban heat island, defined as the difference in temperature between a city and the surrounding rural area, and population size [4]. And the population influence is a significant factor for the observed climate change [5].

Climate change might cause a serious threat to our ecological and socio-economic systems [6-8]. The local climate change due to the rapid urbanization process may be considered, in general, harmful to cities, resulting in the following main problems. 1) It has a direct negative effect on human settlement. It brings the threat to human comfort and health, the loss of social fortune and the impact on economic production. 2) Its effects on the natural environment cannot be neglected. It has influence on all subsystems of ecosystem and has changed the intrinsic ecological order. Therefore, climate consideration should play an important role in the harmonious development between urbanization and eco-environment. Due to the lack of this knowledge, it has been recognized that climate issues often have low impact on the urban development decision. In China, ecological impacts by climate change were considered in the process of the urban planning.

Increasing concern about climate change has recently generated the studies about the effects of urbanization on the mitigation of the urban warming. Many studies have been conducted on the effects of urbanization on the individual factors that will in turn influence climate [2]. For instance, KARACA et al [9], LIN and YU [10] and CHUNG et al [5] showed that the population growth alone could increase urban temperature by human activities. Similarly, WENG and YANG [11] and XU and CHEN [12] quantified the increased heat storage of the expansion of urban areas. AKBARI and KONOPACKI [13] analyzed the relationship between the energy consumption and urban climate strategy. However, the degree of urbanization has been always statistically inferred from several loosely connected properties such as land cover, land use change, construction activities, automobile registration, and energy consumption. Also, there are many researches about the urban thermal environment changed by urban development considering several different factors. BOHM [14] considered that the city Vienna had experienced a particular development period, zero population growth, and the large magnitude increase of dwelling house areas, road areas and energy consumption and decrease of vegetated areas are the main reasons for urban heat island. KING and CYNTHIA [15] analyzed the heat island effect and characteristics of social economy development in 36 cities in southeast of United States, and found the relationship between city development and heat island effect by investigating the population factor, city traffic budget, transport charge, production and the number of retail corporation. In recent years, much more attention has been paid to different factors that affect the urban warming process. BAKER et al [16] elaborated that the phenomena of urban warming had effects on human comfort, production of farming and energy consumption in architecture (refrigeration and heating), and put forward a strategy for reducing and adapting energy supply and demand as well as land use. XIAO et al [17] summarized the effects of urban heat island on urban eco-environment qualitatively.

However, there are still some deficiencies in previous researches on urban heat island and greenhouse effect. The influence on urban eco-environment (including human settlement and natural environment) and the negative effect on urban development with temperature increasing were ignored. The environment impact and planning strategy were researched qualitatively, but not quantitatively. The characteristic of developing countries was never considered. Such information is essential for a better understanding of the sustainability in urban development processes.

The objectives of this study are: 1) to identify the urban warming due to the three prominent urbanization components from 1993 to 2008, and evaluate the weights to the factors of urbanization; 2) to search the possible effects of urbanization on urban warming in Changsha, China.

2 Experimental

2.1 Study area

Changsha is the capital of Hunan Province located 28?02′-28?16′N in the north-subtropical climatic zone with well-defined seasons and an annual mean temperature of 16.9 °C. The maximum temperature exceeds 40 °C in summer, dropping to a minimum of -12 °C in winter. The average annual rainfall is       1 400.6 mm/a, and the rainfall concentrates in summer. The frost-free period is 280 d. The terrain of the Changsha is high in the west and low in the east. And its geologic structure is complex, comprising mountains, low hills, low terraces, plains and rivers (Fig.1). There are many mountainous areas in the west and in the north, and the Xiangjiang River flows from south to northwest.

Fig.1 Position of Changsha in China (a) and Hunan Province (b), and map of urban area of Changsha (c)

Its total area is 556 km², and the built-up area is 242 km², with a population of 2.89 million [18].

2.2 Data sources

Multi-annual socio-economic-environment statistical data and city maps are collected for investigating the impact of urbanization effect on climate change from 1993 to 2008. The materials used in this study are listed in Table 1.

2.3 Methods

2.3.1 Research framework of urbanization climate eco- environment (UCE) system

There are interactive coercing and dynamic relationships between urbanization and eco-environment based on climate change. The key point to make the balance of urbanization and eco-environment is to control urbanization factors that lead to urban climate changes. For this position, quantitative analysis has been done to the urbanization factors working on urban warming, which is essential to realize the relationship among urbanization, climate change and eco-environment (Fig.2).

Three main factors of urbanization have been selected according to Fig.2. 1) Built-up area. Urban areas generally have higher solar radiation absorption and greater thermal capacity and conductivity because of being covered with buildings, roads and other impervious surfaces. Therefore, urban areas tend to experience a relatively higher temperature increase compared with the surrounding rural areas. 2) Total energy consumption. Another growing evidence of environmental problems is due to a dramatic growing of energy consumption. Based on the investigation of energy consumption in Changsha, the main energy types in this city are briquette, coke, oil consumption as gasoline, kerosene, diesel and lubricating oil, gas consumption as natural gas, coal gas, and electricity. To figure out the total energy consumption, all these types of energy have been transferred to standard coal. 3) Population. Urban population denseness (UPD) is also a significant reason of urban heat concentration. It is known that urban heat island effect has extremely close relationship with urban population density and population distribution in different districts of urban areas from the previous research. Based on the analysis of

Table 1 List of materials and data used in this research

Fig.2 Methodologies to analyze urbanization­-climate-eco-environment (UCE) system

the statistic of UPD and energy consumption of Chinese cities, the correlation coefficient is up to 0.887 9. In other word, energy consumption requirement of urban resident would increase by 38 000 000 t of standard coal while urbanization level index enhances by 1%, in case of population extension of China [19].

2.3.2 Mathematical method and calculation process

A time-series analysis of the rate of urbanization is necessary to understand its impact on the thermal environment. A detailed analysis of the temporal variability of the rate of urbanization between 1993 and 2008 in Changsha was conducted. The numerical simulation of local climate was consequently performed to determine the effect of anthropogenic heat on local urban climate. Because variations in temperature are considered to be highly indicative of climatic variations, a significant amount of work has been done using this meteorological parameter [9]. Therefore, while studying the time series of urban warming intensity, the temperature time series are used.

1) Three factors, built-up area, total energy consumption and population as index of urbanization were transformed into dimension-less values using data standard treatment. The equation is shown as

 (i=1, 2, …, n)

where U_i is the dimension-less data of each factor; n is the number of data for each factor from 1993 to 2008 and is equal to 16; x_min is the minimum value of each factor; x_max is the maximum value of each factor; and x_i is the value of each factor. The data are in the range of 0-1 and become dimensionless after the treatment.

2) Analytical hierarchy process (AHP)

The analytic hierarchy process (AHP) is a comprehensive, logical and structural framework, which allows to improve the understanding of complex decisions by decomposing the problem in a hierarchical structure. The incorporation of all relevant decision criteria and their pair-wise comparison allow the decision maker to determine the trade-offs among objectives. The AHP is the most widely used approach for multiple-criteria analyses (MCA). The weights for the three factors are evaluated by AHP according to their effect degrees on surface temperature. It consists of three steps: row vector normalization, row sum up and normalization.

3) Urbanization development is considered to be a nonlinear system and its evolvement process can be expressed as follows:

 j=1, 2, …, m

where f is a nonlinear function of X_i and m is the number of influence factor.

Expand the equation around the origin using Taylor series, and then the equation above can be expressed by

where f(0)=0, and   is an analytical function.

Then, linear system for urbanization is approximately:

(j=1, 2, …, m)                                   (1)

where a_i is the weight of each factor and

u_i is the dimensionless data of the three factors in each year.

3 Results and discussion

3.1 Change trend of population, energy and land use

The population, total energy consumption and built-up area changed from 1993 to 2008 are summarized in Fig.3. The population has an evident increase tendency during this period, changing from 1 097 000 to 2 893 000 persons. The built-up area varies from 101 to 242 km² and there is a sharp ascension during this period. Also, the total energy consumption has increased by approximately 4-5 times in Changsha during this period (Fig.3).

3.2 Urban warming caused by urbanization

3.2.1 Relative evolvement rate of urbanization

During the process of urbanization, the three factors of urbanization are applied to identify the attributions to surface temperature of Changsha. These attributions are translated to the corresponding importance weights by the analytical hierarchy process (AHP), with 0-1 interval scale.

The weight of each factor is introduced to Eq.(1) and the curve is simulated nonlinearly. By analyzing the data of Changsha area, the evolvement rate of urbanization can be expressed as

y=0.000 7 x²-2.768 1 x + 2 715.9 (r² = 0.963)       (2)

3.2.2 Relationship between relative rate of urbanization and surface temperature

According to Fig.4, the temperature in Changsha is increased in annual minimum, maximum and mean temperature during the studied period. The current temperatures are higher than those of the past at all. The temperature conditions and the increase seem to be closely related to the rate of urbanization during the same

Fig.3 Historical trend in population (a), energy consumption (b), and built-up area (c) from 1993 to 2008

period. According to our analysis, the linear model is used to express the relationship between temperature and relative urbanization for the three kinds of temperature, and they are in good agreement with the investigated data. But, the influence extent of urbanization on three kinds of temperature is different. Urbanization effect has a most evident effect on the maximum temperature, compared with the minimum temperature and the mean temperature, and the effec on minimum temperature is the

Fig.4 Effects of relative urbanization on temperature:       (a) Minimum; (b) Maximum; (c) Mean

least.

3.2.3 Attribution of urbanization effects on urban warming

Using Eqs.(1) and (2), the temperature affected by the relative urbanization is calculated. It is theoretically possible to extract the urbanization induced warming from the observed temperature increase, by leaving the factors of regional climate change. According to Fig.5, the maximum warming obtained from the regression model with the increase of urbanization during the same period are attributed to the urbanization. With proportion calculation, there is an evidential increase trend of

Fig.5 Estimated proportion of relative urbanization effects and regional climate changes to urban warming in annual minimum (a), maximum (b), and mean (c) temperature in Changsha

urbanization influence on urban warming during 16 years, compared with the regional climate effect. The effect rates of relative urbanization on the minimum, maximum and mean temperature are 0.499, 0.738 and 0.646, respectively. However, a statistically significant urbanization effect prevails over all these years in the maximum temperature (Fig.5(b)) except 1994 and 1997, and the magnitude is greater than the regional warming. The increase of maximum temperature has been most affected by the urbanization effect. According to this estimation, there is little warming in minimum temperature before 2000. But, there is a sharp rising after 2000.

3.3 Utility and adaptation of methodology in China

The research method adopted to explore the dynamic relationship between the change process of climate and the factors of urbanization worked quite effectively. Though, the interpretation of this question requires a considerable level of expertise and technical skills, the accuracy of factor selection and calculation is still problematic in heterogeneous urban environments. However, it is the most appropriate approach that directly connected the urbanization and climate by far. Cities in the developed countries such as the USA extend many kilometers to suburban areas where peoples reside in and there is as much vegetation as rural areas in the suburban. Whereas, Chinese cities have a significantly higher density of population, residential buildings, shopping malls, schools, roads, etc, and much less vegetation than their neighboring rural areas because of people living within cities. These unique characteristics could make the attribution to urban warming more pronounced in China than in other countries like the USA. Other cities in china could use the same approach to reveal the relationship between urbanization and eco-environment according to their actual situations.

The rational urbanization development policy is one that requires decision makers to acknowledge and conform to the rules of ecological sustainability. In fact, urban planning and design policy could be redesigned to mitigate urban warming, but few cities in China have taken it into account when planning codes and practices. If this approach which is based on a hierarchical analysis of the urbanization factors was implemented, then it would provide a simplified urban development planning procedure to propose a climate-responsive urban development strategy, and meanwhile the sustainable development between urbanization and urban eco-environment would be realized.

4 Conclusions

1) As the most prominent component, the urban surface temperature is used to estimate the impacts of urbanization on climate in Changsha. In the analysis, temperature changes in Changsha influenced by regional climate change are limited from 1993 to 2008. Increase in the maximum temperature is more attributable to urbanization effect than the minimum temperature change.

2) During 16 years, the urban warming in Changsha is mainly contributed to the urbanization factors, and the effect of regional climate change on urban warming is less comparatively.

3) To achieve the objective that making the harmonious development between urbanization and eco- environment based on the quantifiable approach, there are also some deep researches to be done in the future. In order to understand the nationwide climatic atlas, including rural and mountain regions, it will also necessary to join in the rural climatological data at rural stations, using spatial interpolation. Rural climatological data should be analyzed to simulate the ecosystem on climatic change, because the urban area is still much smaller than that of natural and agricultural ecosystems in China.

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(Edited by YANG Bing)

Foundation item: Projects(2008JT1013, 2007JT3018, 05SK3002) supported by the Key Program for Science and Technology in Hunan Province, China; Project(2007ZK2025) supported by the Key Program for Soft Science in Hunan Province, China

Received date: 2010-04-09; Accepted date: 2010-12-04

Corresponding author: LIU Shao-bo, PhD; Tel: +86-13787790105; E-mail: liushaobo23@yahoo.com.cn