Analysis on the Coupling Relationship between Urbanization and Regional Ecological Security and Empirical Analysis

With the acceleration of urbanization, regional ecological security issues have become increasingly prominent. There is a complex relationship between urbanization and urban ecological security. This paper uses the method of system analysis to qualitatively describe the coupling relationship between urbanization system and urban regional ecological security system, and quantitatively evaluate the coupling and coordination relationship between these two systems. The results show that the spatial urbanization subsystem is the most driven to the urbanization system, and the ecological security response system is an important factor to maintain and enhance the urban ecological security. Therefore, the spatial urbanization subsystem and the ecological security response subsystem have the greatest influence on the coupled system between urbanization and urban ecological security. Taking Shaanxi Province as an example, it is analyzed that the coordination degree between Shaanxi's urbanization system and regional ecological security system is increasing from 2005 to 2016, and has experienced four stages : uncoordinated recession, low coordination, moderate coordination and high coordination. The coordination degree between urbanization development and urban ecological security has been continuously improved, indicating that urbanization development has a positive role in promoting urban ecological security.


Introduction
As the objective requirement of the development of modern market economy, urbanization promotes the development of society, the improvement of productivity and the growth of economic efficiency [1] . With the acceleration of urbanization, under the interference of nature and human activities, the ecological environment in the region poses a threat to human survival and sustainable development [2] , and regional ecological security issues are increasingly prominent. At the same time, some studies have shown that the higher the level of urbanization, the greater the negative impact on ecological security in a certain areas [3] . However, in the face of developed European countries, the average level of urbanization has reached 70%, and their ecological security status has not deteriorated significantly, but has improved.
From what has been discussed above, it is not sufficient to think that the development of urbanization will affect the ecological security of urban areas. The main reasons are: 1. Urbanization is a dynamic and multidimensional complex system, which includes many aspects such as population urbanization, economic urbanization, social urbanization, landscape urbanization, etc., and there are complex interactions between them. 2. Regional ecological security is also a complex and comprehensive state, which includes three aspects: natural ecological security, economic ecological security and social ecological security [4] . Therefore, there is no simple relationship between urbanization and regional ecological security. Therefore, a scientific understanding of the relationship between urbanization development and urban regional ecological security is of great significance for a country and a region to formulate urbanization strategies that are conducive to urban regional ecological security in the future.
2 Identification of the relationship between urbanization and regional ecological security 2.1 The positive impact of urbanization on regional ecological security Firstly,the reduction of rural population has alleviated the pressure of agricultural resources and rural ecology, which has produced good environmental benefits. Due to the increase of urban population and the increase of social investment in cities, urban areas have been better developed. In this way, more rural population will come to the city, their education level will be improved correspondingly, and the population quality of the whole society will be improved. All these factors have an important positive impact on urban ecological security [5][6] . Secondly, as the city's economic development level improves, the urban economic structure is optimized, and the relationship between population, resources and environment is gradually coordinated, which have positively improved the ecological security of urban areas [7][8] . In the end, the development of urban social undertakings will promote the scientific management of urban management, and at the same time promote the widespread spread of ecological civilization concept among urban residents, which will deeply influence people's lifestyle. In the long run, it has far-reaching significance for improving the urban ecological environment and promoting regional ecological security.

The negative impact of urbanization on regional ecological security
Firstly, the development of industry also brings about serious air pollution, and the modern city high-rise buildings are piled up, making the pollutant not easy to dilute and spread, which has a serious negative impact on people's health. Secondly, as the city expands outward, the structure of land use changes accordingly. When the urban system is not yet perfect, the impact of urban space expansion on the ecological environment is mainly reflected in the increase of the construction land area and the continuous reduction of land area such as arable land, woodland, grassland and wetland, the loss of ecosystem service value and the enhancement of urban "heat island effect". Industrialization has indeed improved people's living standards, but it has brought about serious ecological pollution and environmental damage.

Construction of Coupling Measure
Model of Urbanization and Regional Ecological Security

Index system construction
Urbanization is a comprehensive manifestation of many aspects. Therefore, it has multidimensional characteristics: in terms of population, it refers to the proportion of urban population; in terms of space, it refers to the continuous expansion of urban area; in terms of industry, more nonagricultural economy has replaced agricultural economy; In terms of social culture, it means that urban-related lifestyles and life concepts are spread and popularized [9] .
According to the characteristics of urbanization and following the principle of selection of indicators, this paper combines the actual situation of social development and the availability of data, and refers to related research [10][11] . Finally, four comprehensive indicators of the first-level indicators and 13 secondary indicators are formed, as shown in Table 1. Regarding ecological safety assessment, there are many types of models used in domestic and foreign literature, such as PSR model, DSR model, DPSER model, etc [12][13][14] . Currently widely used is the Pressure-State-Response Model (PSR), which was jointly proposed by the Economic Development Organization (OECD) and the United Nations Environment Programme (UNEP). This paper uses the PSR model to construct an ecological safety assessment model.
The stress-state-response model, in which "stress" refers to the cause of ecological safety problems, this paper selects the pressure factors of land, resources and environment; "state" is used to measure the state of human caused natural environment. Based on data availability and comparability, this paper selects two indicators of resources and environment; "response" refers to the ability of human beings to cope with ecological security crisis. This paper selects three elements of pollution control, economic input and humanities and society to reflect. Finally, referring to the relevant literature, according to the relevant principles, the urban ecological security evaluation index system constructed is shown in Table 2.

Termination of the weight of evaluation indicators
In this study, the entropy weight coefficient method is used to assign weights to two system indicators. The calculation steps are as follows: ① Data standardization processing: since the dimensions and magnitude of each indicator and the positive and negative orientations of the indicators are different, the initial data needs to be standardized. For the positive and negative categories of indicators, the standardization method is as follows: In this formula： ' X ij and X ij are the standardized and original values of the j item in the i year. The max X j and the min X j , they are the maximum and minimum values of the j-th single indicator for all years. Where m is the number of years of evaluation and n is the number of indicators.

Thesis of Urbanization and Regional Ecological Security Evaluation Indicators
For the urbanization level index, the 27 indicators data of population, economy, society and space are first standardized, then the weight calculation is performed by the entropy weight method, and the urbanization level index of 4 aspects is obtained by weighted summation. These four aspects of the urbanization level index are multiplied by the corresponding weights, and after accumulating, the comprehensive urbanization level index is obtained [15] .
The calculation formula: In this formula ： M is the comprehensive urbanization level index; f i is the urbanization level index of population, economy, society and space, and w i is the corresponding weight.
Similarly, a weighting function is used to derive the development index of the urbanization and ecological security system and its various subsystems. Its calculation formula is: In this formula： and ( ) f Y are the combined values of the urbanization system and the urban regional ecological security system development index. Their numerical values are positively correlated with the corresponding urbanization level and ecological security status.

Construction of Coupling Relationship Model between Urbanization and Regional Ecological Security
Extending the coupling degree model of multiple systems by means of the coupling concept in physics, The coupling evaluation model of urbanization and ecological security can be obtained as follows: In this formula：C is the coupling degree between urbanization system and ecological security system , it reflects the degree of interaction between the two systems; T is the comprehensive evaluation index of the development level of urbanization system and ecological security system; p and q is the weight coefficient , reflecting the degree of influence of the two systems on the urbanization-ecological safety coupling system; D is the degree of coordinated development ( 0 1 D ≤ ≤ ),it measures the degree to which the two systems are in harmony with each other during development. Here, the difference between the degree of coupling and the degree of coordinated development is that the degree of coupling mainly reflects the degree of interaction between systems, it does not indicate right or wrong; and the degree of coordinated development indicates the degree of benign coupling in the interaction, reflecting the degree of coordination.
According to existing research, the coupling relationship between urbanization and urban ecological security can be divided into four categories according to the size of coordinated development degree D; These four categories can be divided into 12 different coupling coordination types according to the size relationship between ( ) u X and ( ) f Y (as shown in Table 3), and the coordination and development of the two systems are judged accordingly.

Empirical analysis 4.1 Research objects and data sources
This paper takes China's Shaanxi Province as the research object, and empirically analyzes the coupling relationship between urbanization and urban regional ecological security. The relevant indicators in the urbanization

Analysis of urbanization system results and changes in urban area ecological security system
The weights of each index of each subsystem of urbanization and the three sub-systems of urban area ecological security are obtained by Matlab. For the urbanization system, the population urbanization subsystem has the greatest weight, followed by the social urbanization subsystem and the economic urbanization subsystem, and the smallest is the spatial urbanization subsystem. It also shows that it is reasonable to use the proportion of urban population to reflect the overall development level of urbanization. According to the 13 individual indicators of the urbanization system, the three indicators that have the greatest impact on the urbanization system are the per capita urban road area, the number of beds per 10,000 people, and the per capita industrial output value.
In the urban regional ecological security system, the response subsystem has the largest weight, followed by the pressure subsystem, and the state subsystem has the least effect in the urban regional ecological security system because of the least indicators. Through this result, we can draw the conclusion that the specific measures for ecological security issues are the most important for improving and maintaining ecological security.
For China with a large population, the urbanization process is accelerating and the urban population density is increasing. Improving urban infrastructure construction, improving laws and regulations, and introducing corresponding supporting safeguard measures have become the key factors determining whether urban ecology is safe. Therefore, in the process of exploring the coordinated development of urbanization and ecological security, the ecological security response must be considered.

Analysis of Coupling Changes between Urbanization and Urban Regional Ecological Security
Regarding the quantitative study of the coupling relationship between the two systems, most of the literature [15][16] directly gives the same weight to the two systems(p=0.5,q=0.5).In this paper, by changing the values of p and q, three different scenarios are set to analyze the changes in the coupling relationship between urbanization and urban ecological security. The specific results are shown in Table 4.

A
Comparing the coupling situation between urbanization and urban regional ecological security system under three conditions, the development trend of the coupling coordination degree of the two systems under different weights is very small, and the types of coordinated development are basically the same, which indicates the urbanization system and ecology. The coordination degree of the security system is not sensitive to the weight change it gives, which proves that most of the existing researches are reasonable only for the equal weight processing of the two systems.
From Figure 1, during the period of 2005-2016, the coordination degree of urbanization and ecological security systems in China showed a general growth trend. From Table 3, it can be concluded that, according to the degree of coordination and the comprehensive development value of the urbanization system and the ecological security system, the coordinated development has experienced four stages: from uncoordinated recession to high degree of coordination: (1) In 2005, D=0.2225 (p=0.5, q=0.5), the urbanization system and the ecological security system belonged to the uncoordinated recession development, and the degree of urbanization development was slightly lower.
(2) In 2006-2012, the two systems belonged to a lowlevel coordinated development stage. Further analysis, from 2006 to 2009, urbanization development lags behind ecological security development, and from 2009 to 2012, the urbanization process accelerated, and the development of ecological security lags behind urbanization.
(3) In 2013-2015, the coordinated development of the two systems has improved and is in a moderately coordinated development stage. However, in the past three years, the development of urban ecological security has lagged behind the development of urbanization.
(4) In 2016, the urbanization process and urban ecological security reached a stage of highly coordinated development, but they still could not develop simultaneously, and the development of the ecological security system still lags behind the development of urbanization. In recent years, the level of urbanization in Shaanxi Province has been accelerating. As of 2016, the urbanization rate of permanent residents has reached 55.34%, and people's awareness of environmental protection has also increased. However, compared with the speed of urbanization, the development speed of ecological security is still need to be further improved. In the future economic and social development process, ecological security will be the main limiting factor for the coupling system of urbanization and ecological security. Therefore, accelerating ecological security construction is the first problem to be solved in the future realization of sustainable economic development in Shaanxi Province.

Conclusions
Urbanization promotes social progress, promotes economic growth, promotes the improvement and perfection of urban functions, and enhances urban ecological security. However, many urban diseases brought by urbanization seriously affect the ecological security of urban areas. This paper establishes a coupled measure model by identifying the relationship between urbanization and urban regional ecological security. Shaanxi Province was selected as an empirical research object to analyze the coupling relationship between urbanization and urban regional ecological security from 2005 to 2016. The research conclusions are as follows: (1) The positive impact of urbanization on urban ecological security. With its resource advantages, the city attracts people from rural to urban areas. The urban population has increased, the city has expanded in scale, and the level of urban economic development has improved. As a result, the investment in all aspects of the city has increased and the urban economic structure has been continuously optimized. All of this contributes to improving the ecological security of urban areas.
The negative impact of urbanization on urban ecological security. The urban population has increased, the amount of domestic garbage generated has increased significantly, and garbage disposal has not been timely, which has had a great impact on the ecological environment. The expansion of urban area, the reduction of land area such as wetlands and forest land, led to the imbalance of ecosystem functions. A reduction in the area of cultivated land will lead to a decline in food production and will threaten the survival of our people in the long run.
(2) As a city in western China, Shaanxi is less urbanized and economically developed than in the east, and its ecological environment is relatively fragile. Despite this, from 2005 to 2016, the coupling and coordination degree between urbanization and urban ecological security in Shaanxi Province has been continuously improved. From the uncoordinated recession phase in 2005 to the low-coordinated development phase in 2006-2012, to the moderately coordinated development phase in 2013-2015, and to the highly coordinated development phase in 2016. This shows that although urbanization and urban ecological security are contradictory in some respects, overall, the coordination between urbanization and urban ecological security continues to increase. This shows that urbanization development has a positive role in promoting urban ecological security. This also explains why many developed countries have high levels of urbanization, but urban ecological security has improved.