4.2. Mechanisms of the Spatio-Temporal Evolution of Urban-Rural Integration
Internal influence factors have a direct effect on the changes of the spatio-temporal pattern of urban-rural integration. Meanwhile, external factors affect urban-rural integration by influencing the internal elements and structure of the urban-rural system. Therefore, the determination of internal influence factors is the premise and basis for the in-depth analysis and understanding of the dynamic mechanism of urban-rural integration. A geographical detector model is used to detect the factor determinants of various indicators within the urban and rural system; only the top 10 main influencing indicators are listed. As can be seen from
Figure 4, in 2008, 2011, 2014, and 2018, the indicators with a frequency of greater than 3 mainly included X1, X2, X3, X5, X6, X9, X11, X14, and X15. The results show that the driving force of urban-rural integration in shrinking cities is firstly manifested by the centriolar transfer of peripheral regional elements brought about by urban economic, ecological and social advantages. Central cities also play an important leading role in urban-rural integration development. Second, the driving force is manifested by the industries and service linkage between urban and rural areas, which are promoted by the development of rural non-agricultural industries. However, the effect of these factors is generally weak, which is the main reason for the slow development of urban-rural integration in China’s shrinking cities [
48].
Driving factors of urban economic efficiency. The spatial and temporal pattern of urban-rural integration in shrinking cities is highly correlated with the spatial differentiation of urban economic efficiency indicators. The influence of each indicator in the subsystem of urban economic efficiency is large and appears repeatedly. In fact, X3 appears four times, and X1 and X2 both appear three times. This finding shows that the urban-rural economic integration of shrinking cities is more reflected by the radiation of the commercial service functions of central cities to the periphery. However, the sluggish industrial development and the limited urban economic growth cause X1 and X2 to have a relatively weak drive to the periphery villages.
Driving factors from urban resources and environment. In the factors with strong effects on urban-rural integration, X5 and X6 both appeared four times. These results show that the agglomeration and diffusion capacities of cities with different spatial scales are the main reasons for the formation and evolution of the spatial differences of urban-rural integration. For example, Jilin, Zhenjiang, Huzhou, Zhoushan, Taian, Xiangyang, Changde and Zibo, with a high level of urban-rural integration, all have a population of more than 1 million. From 2008 to 2018, the number of national development zones in the eight cities increased from three to 11. Large-scale urban spatial growth drives the increase of population in central cities and further affects the urban-rural integration of shrinking cities. At the same time, the differences in the ecological environment in shrinking cities, as well as other factors, also affect the migration of rural population to cities, thereby easily playing a role in the spatial differentiation of urban-rural integration.
Driving factors of urban social equity. In this study, X9 and X11 have significant effects on urban-rural integration; the frequency of occurrence is three. The employment opportunities and living conditions of shrinking cities are positively correlated with their economic development and industrial structure. The shrinking cities in the eastern, southern and large urban agglomerations have a high level of urban-rural integration. In addition, the important influencing factors are the strong attraction of urban employment and better social service facilities. On the other hand, the central cities in the marginal areas of the northeast, northwest and in the resource-based areas are small in scale, and their historical problems are serious. Moreover, the government cannot afford the required urban construction costs, and as a result, the lack of urban functions leads to the cities’ weak agglomeration ability and the serious backwardness of urban-rural integration.
Driving factors from rural economic efficiency. In this study, X14 and X15 both appear three times, thereby representing bottom-up urban-rural economic correlation. However, rural urbanization on the peripheries of shrinking cities in the eastern and central regions started early. Additionally, the counties on the peripheries of cities such as Huzhou and Huangshan have national high-tech industrial development zones. A good non-agricultural industrial foundation is the premise for a close connection between urban and rural areas.
4.3. Diagnosis of Obstacle Factors of Urban-Rural Integration
Exploring the obstacles to urban-rural integration in China’s shrinking cities is of great significance in terms of improving the sustainability of their urban-rural relationship. An obstacle degree model is used to measure the obstacle degree of each sub-indicator and subsystem of the shrinking urban and rural system. An obstacle factor diagnosis is also carried out according to the frequency and magnitude of the obstacle degree.
4.3.1. Obstacle Factors of the Indicator Layer
The top 10 indicators of obstacle degree over the years were taken as the main obstacle factors, and the occurrence frequency of the main obstacle factors was statistically analyzed. As can be seen from
Table 4, X4, X5, X6, X9, X14, X15, X16, X17 and X22 were the main obstacle factors from 2008 to 2018. In addition, X13 only played an obvious obstacle role from 2008 to 2011, while X18 had an increasing obstacle degree after 2012. This shows that: (1) the obstacle factors of urban-rural integration in shrinking cities are relatively stable. These factors mainly include insufficient urban fixed asset investment, the slow advancement of space development, the need for an improved living environment, the scarcity of jobs in central cities, rural economic strength and the limited number of non-agricultural industries. All of these factors lead to the low development level of rural residents’ income growth and large numbers of the surplus rural labor force shifting to areas outside the shrinking cities. (2) In terms of time change, the influences of urban investment, employment and environmental conditions are gradually strengthening. This finding indicates that the development weakness of the shrinking cities has not been significantly improved. Meanwhile, the non-agricultural industries on the rural periphery of the shrinking cities have developed to a certain extent; their obstacles have also weakened.
4.3.2. Obstacle Factors of Subsystem Layer
The subsystem layer is more generalized than the indicator layer. The time series analysis of the obstacle factors of the subsystem layer in each year was conducted, and the results are shown in
Table 5. The results show that, from 2008 to 2018, the obstacle degree of the rural economic efficiency subsystem was the largest, followed by the urban economic efficiency subsystem. However, the former decreased continuously while the latter gradually strengthened. The subsystem of social equity in both urban and rural areas also has strong influence, and both of them show an increasing trend. The obstacles in the field of resources and environment were the least impactful. During most of the study period, those in the field of urban resources and environment decreased, while those in the field of rural resources and environment increased; they were equal in 2018. Therefore, in order to guarantee the rural-urban integration of shrinking cities, attention should first be paid to economic transformation and development. Then, steps should be taken to strengthen the ability to resist social risk and to revitalize social development. At the same time, strengthen the regulation and guarantee of ecological carrying capacity should be strengthened.
4.3.3. Division of the Spatial Resistance Pattern
Taking the average obstacle degree of the subsystem layer > 33.33% as the principle to identify the resistance of each shrinking city, the spatial resistance patterns are divided according to different cities (
Table 6). The results show that each shrinking city has more than two subsystems of resistance. This finding indicates that a single subsystem does not constitute an obstacle to urban-rural integration. It is therefore necessary to comprehensively consider the degree of obstacles of each subsystem, in order to analyze the resistance mode. The resistance models of urban-rural integration in China’s shrinking cities include three categories of two-system, three-system and four-system resistance models, which can be further divided into 10 subcategories.
In the two-system resistance modes, 16 cities belong to the type whereby both urban and rural economic obstacles are prominent. These cities are mainly concentrated in the northeast and northwest of China. Zibo has a high level of urban-rural integration and less resistance in economic development and is the only city whose urban-rural integration is hindered by the resources and environment of both urban and rural areas. Therefore, Zibo needs to pay attention to the sustainable development of both urban and rural resources, as well as the environment. Taian has the greatest number of obstacles in the field of urban economy and rural resources and environment. The city’s urban-rural integration will require strengthening the urban economy, while at the same time taking the rational development and utilization of rural resources and environment into account.
In the three-system resistance models, the level of urban-rural integration in Zhenjiang is the highest. There, the economic foundation of urban-rural integration is good. The obstacles to future development in Zhenjiang come from the issues of urban and rural resources and environment protection, as well as the urban social subsystem. The urban-rural integration of Zhoushan requires enhancing the level of urban economic and social development, and taking the rural ecological environment into account. Liaoyuan and Huangshan are less restricted by resources and environment conditions, but the urban and rural economic resistance and urban social obstacles in these two cities are obvious. The largest numbers of shrinking cities are those that need to consider urban economy, rural economy and rural social equity barriers, or those that need to consider urban economy, rural economy and urban-rural resources and environment at the same time. This group is mainly comprised of the old industrial cities and resource-based cities in inland areas. Their urban economic development is weak, and their left-over historical social and ecological problems are serious.
Among the four resistance modes, Huzhou and Suining are the two cities that need to consider the resistance of urban and rural economy, urban and rural resources and environment; the obstacles of urban and rural social development are relatively small. The urban-rural integrated development of Tongliao, Jilin and Nanping not only faces the obstacles of urban and rural economic efficiency, but these cities must also consider the obstacles of rural social equity and urban resources and environment.