1. Introduction
At present, the whole world, especially Asia, is experiencing rapid urbanization. The rapid urbanization has brought about the obvious expansion of the city, which seems to indicate that the city will grow for a long time or even infinitely under the tide of population increase, economic growth and area expansion [
1]. However, the phenomenon of urban shrinkage since the second half of the 20th century has broken this inference. UN-HABITAT points out that during the period of 1970–1990 and 1990–2014, the ratio of cities which experienced population loss remained at around 10% globally. Relevant research also finds that the phenomenon of population loss appeared in the process of urban development of developed countries such as Germany, Japan, and the United States and developing countries represented by China [
2]. People have to admit that urban shrinkage has gradually evolved into a global problem, and the phenomenon of its population reduction has brought severe challenges to the comprehensive competitiveness of cities, which has become an urgent problem to be solved in the fields of urban planning and regional research. Under this background, the urban vitality, which is one of the important representations of the high-quality development of the city, has become a new breakthrough idea, gradually appearing in the context of urban development based on pervasive shrinkage [
3]. As one of the actual expressions of the exuberant vitality of urban space, urban vitality reflects the ability and potential of cities’ development to a certain extent and becomes a new source of urban competitiveness. Nowadays, under the realistic predicament that the phenomenon of urban shrinkage continues to appear all over the world, more and more scholars advocate awakening the vitality of cities and realizing the goals of the high-quality development of cities by adjusting the vital elements of cities and improving cities’ comprehensive competitiveness [
4]. The phenomenon of population reduction and negative economic growth caused by urban shrinkage seems to have become an important obstacle to urban development, and the promotion of urban vitality is a breakthrough to solving this problem naturally. Therefore, it is time for academia to further sort out the relationship between urban shrinkage and urban vitality, find out the theoretical and logical connection between urban shrinkage and urban vitality, and then better guide cities to enhance urban vitality in the process of shrinkage in order to help cities obtain stronger development power and complete the transformation from general urbanization to high-quality development.
Since the German scholar, Häußermann put forward the concept of urban shrinkage in 1980s, urban shrinkage has always been one of the hot words in urban research [
5]. At present, scholars from all over the world study urban shrinkage by mainly focusing on connotation interpretation, type identification, planning response, etc. (1) For connotation interpretation, current scholars believe that there are two definitions of urban shrinkage including a narrow and broad definition. The narrow sense of urban shrinkage is mainly characterized by the reduction of absolute population. Shrinking City Research Network defines urban shrinkage as a phenomenon of a city with at least 10,000 people, with population loss of more than two years, structural crisis and economic transformation [
6]. Shrinking City Project holds that urban shrinkage should meet the requirements of population loss of more than 10% and more than 1% population loss every year [
6,
7]. However, with the deepening of research, some scholars suggest that cities are spatial entities formed by the interactions of population, economy and space, and the reduction of population cannot fully reflect all the characteristics in the process of urban shrinkage, which is accompanied by the adjustment of economic structure and the change of social environment. Therefore, they believe that urban shrinkage in a broad sense should take into account the changes in population, economy, space and environment, etc. [
2,
8,
9,
10,
11]. It is worth mentioning that, regardless of the definitions, scholars have reached a consensus that the process of urban shrinkage is accompanied by the loss or attenuation of urban development elements. Under the background of the scarcity of urban development resources, its comprehensive competitiveness will inevitably be affected by this, resulting in the decline of advantages of location and the weakness of urban development. (2) For the identification of urban shrinkage types, the current scholars mainly use three identification types: population change rate division, spatial form division and shrinkage cause division. According to the change rate of shrinking urban population, Chen et al. [
12] divided the shrinkage types into isolated shrinkage, continuous shrinkage and staggered shrinkage by studying the urban shrinkage in the Yellow River basin from the perspective of population. According to the population and economic data of Liu et al. [
13], the shrinkage types are further divided into absolute and relative shrinkage. According to the shrinking urban space form, it can be divided into “perforated”, “doughnut” and “peripheral” types. According to the relationship between shrinking cities and surrounding cities, it can be defined as marginal core dependent shrinkage [
14]. (3) For planning response, scholars mainly try to solve the development problems of shrinking cities with ideas such as “resilient city”, “smart shrinkage” and “inclusive city” [
15,
16], trying to improve urban vitality from several aspects in order to solve the development problems of shrinking cities.
The concept of urban vitality originated from Jacobs’ description of active street life created by a large number of pedestrians [
17]. Since then, scholars have never reached a unified understanding of urban vitality: Maas holds that successfully maintaining a vibrant area depends on street life and its social interaction; Landry thinks that economic, social and physical environmental factors interact to form vitality [
17,
18]. At the same time, the existing related study areas are mostly concentrated on streets and neighbors. Although different scholars pay different degrees of attention to urban vitality, which leads to various expressions, it has become a consensus that urban vitality has many attributes such as economy, society, culture and multiple influencing factors. Therefore, different from the treatment of street vitality as urban vitality based on Jacobs’ theory, nowadays, there are many definitions focusing on the macro meaning of urban vitality in the academia. From the perspective of urban sociology, urban vitality is regarded as a concrete representation of urban competitiveness, which is subdivided into three parts: economic vitality, social vitality and cultural vitality, showing the ability of cities to provide facilities and space for urban residents’ activities [
19]. At the same time, as for the measurement methods of urban vitality, plenty of scholars measures urban vitality on the street scale based on global positioning system, point of interest (POI), mobile phones, integrated circuit cards, taxis and other data and there are also some scholars who measures the urban vitality in a macro sense according to urban statistical data, bulletins and yearbooks [
20]. It is worth noting that more and more scholars have applied urban vitality to other fields, such as sociology, criminology and public health, etc., and have started a critical reflection on the past urban expansion through the possible impact of urban shrinkage on urban vitality [
21,
22,
23].
Generally, although there have been many related studies on urban shrinkage and urban vitality, their connotation, measurement, cause identifications and response of plannings have all been discussed, little research has been done on the correlation between them, especially the urban shrinkage and urban vitality correlation researches, which should be an innovative direction. However, from the existing unilateral researches on urban shrinkage or urban vitality, we can find the possible internal relationship between them: Firstly, because each city is a spatial complex with multiple factors, the influencing factors related to its development are often diverse, so the evaluation system constructed by the related researches on urban shrinkage and urban vitality often has a strong correlation, which is reflected in economic, social and environmental indicators; Secondly, the changes of urban development factors in the process of urban shrinkage often leads to the decline of urban competitiveness, and urban vitality is regarded as one of the specific manifestations of urban competitiveness. Therefore, the process of urban shrinkage often leads to the corresponding fluctuations of urban vitality, which is finally reflected in the comprehensive level of urban competitiveness. Thirdly, the decision makers can boost the urban vitality in the reverse direction through the concepts of smart shrinkage and resilient city, and they also put forward the advocacy of “plans of shrinkage” accordingly [
16,
23,
24,
25]. On this basis, this paper holds that there is a certain logical connection and mechanism between urban shrinkage and urban vitality. In a word, urban shrinkage and urban vitality show a certain degree of correlation because they jointly influence urban development and eventually settle down in urban competitiveness. However, considering the diversity of influencing factors, the relationship between urban shrinkage and urban vitality cannot be simply understood as a simple linear relationship with the same increase and decrease, or a trade-off between the increase and the decrease. Urban shrinkage and urban vitality form their own systems, and each system has constantly changing elements and subsystems corresponding to different indicators. The systems are connected by indicators with common or similar points, which then interact with each other. The results of these interactions can often reflect the specific relationship between the two systems, which shows the correlation between urban shrinkage and urban vitality (
Figure 1). Furthermore, the influencing factors of urban vitality are diverse, and the degree of correlation between urban shrinkage and urban vitality will also be differentiated due to different dimensions of urban vitality. Based on the thinking and speculation, this research starts with urban shrinkage and urban vitality, respectively, identifies and measures each of them, and then analyzes and explores their relationship with the method of correlation analysis. Exploring the relationship between urban shrinkage and urban vitality in the aspects of economy, society, culture, etc. has a considerable effect on the deep excavation of urban vitality of shrinking cities, and the results will directly guide the urban development planning of cities experiencing shrinking and have an enlightening effect on the research direction of shrinking-cities planning [
26,
27]. Therefore, the research on the correlation between urban shrinkage and urban vitality should be put on the research agenda as soon as possible to solve the existing theoretical dilemma and practical problems.
3. Results
3.1. Basic Situations of Urban Shrinkage in the Three Northeastern Provinces of China
After the identification by “two-step diagnostic method”, this research obtains the basic situation of urban shrinkage in the three northeastern provinces of China from 2010 to 2018. As shown in
Table 4, the urban shrinkage in the three northeastern provinces of China has following characteristics: (1) From 2010 to 2018, 21 cities have shrunk in different degrees, which reflects the general trend of urban development in the three northeastern provinces of China. According to the identification by “two-step diagnostic method”, except Harbin, Daqing, Mudanjiang, Heihe, Changchun, Liaoyuan, Songyuan, Shenyang, Dalian, Jinzhou, Yingkou, Panjin and Chaoyang, the other cities have experienced urban shrinkage of different scales, and the number of these cities is more than that announced by the Ministry of Housing and Urban-Rural Development of China in April 2019. (2) Among the 21 shrinking cities, 15 cities have passed the second judgment, that is, there are other shrinking phenomena except population shrinking. From this, it can be preliminarily judged that urban population shrinking is likely to trigger the subsequent shrinking process, resulting in regional urban shrinking phenomenon. (3) According to the identification results, there are nine cities in the middling shrinkage stage in the three northeastern provinces of China. Middling shrinkage generally shows that the population is greatly reduced or slightly reduced, while other indicators are obviously reduced. (4) Generally speaking, the phenomenon of urban shrinkage in the three northeastern provinces of China is not a single case, but it has shown certain regional commonalities and inter-city differences. Urban shrinkage is widely distributed in the three northeastern provinces of China, accounting for 61.76% of the total number of cities. At the present stage, urban shrinkage is an inevitable process of urbanization, and its relationship and function with urban vitality are worth exploring, with a view to providing ideas for urban development in the three northeastern provinces of China and even other regions [
4].
3.2. Spatial Characteristics of Urban Vitality in the Three Northeastern Provinces of China
Table 5 shows the changes of urban vitality values and rankings of cities in the three northeastern provinces of China from 2010 to 2018. In order to intuitively reflect the spatial pattern and temporal evolution of urban vitality in the three northeastern provinces of China, this research uses ArcGIS to display the annual urban vitality values of each city on the maps (
Figure 3). When mapping, this research selects the natural breakpoints of the comprehensive scores of the middle year (2014) as the natural breakpoints of all years for grading display, which can show the absolute size and relative level of urban vitality at the same time and can more scientifically show the temporal and spatial change process of urban vitality.
It can be seen from
Figure 2: (1) In the nine years, the urban vitality in the three northeastern provinces of China shows an overall upward trend, while the values of most cities fluctuated, not rising and falling steadily. (2) The high values of urban vitality in the three northeastern provinces of China show a trend of gathering towards centers, that is, the three provincial capitals and Dalian become the center of the region, respectively, which promotes the value of surrounding cities to rise and forms a large-scale and regional linkage when their own urban vitality is at a high level for a long time. Previously, a large number of studies have shown that in Asia, places with high urban vitality are often located in central cities [
37]. This research reveals that in the three northeastern provinces of China, the places with high urban vitality are all in the cities with strong central characteristics, such as Harbin, Changchun, Shenyang and Dalian. (3) The urban vitality of the three northeastern provinces of China, especially the Liaodong Peninsula city group, is generally rising but polarized towards the middle. (4) The vitality of cities in northern Heilongjiang, southern Jilin and western Liaoning has been sluggish for a long time, changing little, and it has not been led by other cities to develop. Based on the existing theories and the above analysis, this paper speculates that there is a certain correlation between urban shrinkage and urban vitality in the three northeastern provinces of China, which is worthy of further exploration.
3.3. The Relationship between Urban Shrinkage and Urban Vitality
According to the method and process of correlation analysis, this research finds that there is a significant positive correlation between the comprehensive scores of urban vitality and the scores of urban shrinkage in the three northeastern provinces of China from 2010 to 2018. However, it is worth noting that the urban shrinkage scores used in the research are negative, and the positive correlation only aims at the change between the two scores themselves and does not reflect the relationship between urban shrinkage and urban vitality. Specifically, the more serious the urban shrinkage, the lower its urban vitality. From 2010 to 2018, the correlation coefficient values are 0.386, 0.451, 0.438, 0.469, 0.488, 0.457, 0.463, 0.437 and 0.457, respectively, all of which pass the significance test. The result shows that the degree of urban shrinkage of cities in the three northeastern provinces of China will have a positive impact on the relative size of urban vitality, and the impact reaches its peak in the middle year (2014).
According to the index systems of urban shrinkage and urban vitality, the relationship between urban shrinkage and urban vitality is understandable. In a certain year, the more obvious the shrinkage phenomenon is, the lower its urban vitality is. It has been proved that there is a strong correlation between urban shrinkage and urban vitality in time and space. The correlation coefficient value between urban vitality and the urban shrinkage reaches the highest value in 2014, indicating that the change of urban vitality in 2014 is in the middle stage, which can represent the average level of urban vitality in nine years to a certain extent. The correlation coefficient value between the comprehensive urban vitality score and the urban shrinkage score is the lowest in 2010, because 2010 is the starting year of this research, so the trend of urban shrinkage of that year cannot be judged.
To sum up, urban shrinkage is the result of a long period, while urban vitality is the value that changes yearly. They represent the stage state and real-time capability of cities, respectively. The correlation shows that different degrees of urban shrinkage have different effects on urban vitality. At present, for the whole region, urban shrinkage has shaped the spatial pattern of urban vitality. For some cities, urban shrinkage slows down the promotion of urban vitality, but it does not completely limit the exertion of urban vitality.
However, from 2010 to 2018, although urban shrinkage and urban vitality are significantly correlated, the correlation coefficient values are not more than 0.5, that is, they are not completely correlated. It suggests that the role between urban shrinkage and urban vitality is actually complex and diverse, which needs further exploration and analysis.
3.4. The Relationship between Urban Shrinkage and Various Dimensions of Urban Vitality
In order to explore the specific impact of urban shrinkage on urban vitality, this research conducts correlation analysis between the comprehensive scores of economic vitality, social vitality, cultural vitality, environmental vitality and spatial vitality of cities in the three northeastern provinces of China from 2010 to 2018 and the urban shrinkage scores (
Table 6) and compares the five groups of results.
The correlation coefficient values of comprehensive economic vitality scores and urban shrinkage scores are 0.363, 0.401, 0.386, 0.402, 0.411, 0.398, 0.426, 0.408, 0.411, respectively, all of which show 0.05 level significance. The results show that there is a significant positive correlation between urban economic vitality and urban shrinkage, and the change trend of correlation coefficient value is similar to that obtained by the above analysis. This result is not unexpected. According to the method of this research, the judgment of urban shrinkage cannot be separated from economic factors. The economy of the cities in the shrinkage stage often does not perform well, such as the sharp drop of foreign investment, the imbalance of industrial structure, and the shrinking of market scale. The shrinkage of various economic indicators in cities naturally leads to the reduction of economic vitality.
The correlation coefficient values of comprehensive scores of urban social vitality and urban shrinkage scores are generally low, and only the data of 2016 pass the significance test. It can be shown that, the correlation between urban social vitality and urban shrinkage is weak. This is because the mechanism of urban shrinkage on social vitality is different from that on economic vitality. Although social vitality is related to population, urban shrinkage is a comprehensive and phased process, which cannot be completely summarized by population changes. Moreover, the indicators of social vitality have been stripped of dimensions, often reflecting the average level of every 10,000 people, so the change rate of data is buffered. At the same time, the social vitality base of each city is quite different, so it is not affected by urban shrinkage obviously.
The correlation coefficient values between the comprehensive score of urban cultural vitality and the score of urban shrinkage show a trend of first increasing and then decreasing on the whole, with the data in 2012 reaching the peak, and the data in 2017 and 2018 failing the significance test. There is a certain correlation between the cultural vitality and the urban shrinkage, but this relationship gradually weakens after reaching the peak. On the one hand, culture belongs to people’s high-level needs, and it also represents the historical origin and spiritual wealth of cities. Urban shrinkage brings new challenges to urban population and economic and social development, which will have an impact on the vitality of urban culture, and therefore there is a certain correlation between the two. On the other hand, in recent years, China has taken the road of cultural self-confidence, pays more and more attention to the excavation and construction of urban culture, and actively promotes the upgrading of cultural vitality. Therefore, the impact of urban shrinkage on cultural vitality gradually decreases.
The correlation coefficient values of urban environmental vitality comprehensive score and urban shrinkage score fluctuates greatly in nine years, among which the data of 2010, 2012 and 2013 fails the significance test, and the correlation coefficient values of other years fluctuates obviously, not displaying specific laws. Therefore, there is a certain correlation between urban environmental vitality and urban shrinkage, but the degree of correlation between them is not clear and changes at any time. The vitality of the environment mainly reflects the ecological value, sanitary quality and supply capacity of the city. According to China’s national conditions, the first two indicators generally increase year by year and will not decrease with the shrinkage of the city. Urban shrinkage affects the overall level of social production through a series of changes in population, economy and society, coupled with the special climate in the three northeastern provinces of China, which in turn can change the supply capacity of cities to a certain extent, such as causing a temporary regional shortage of coal and electricity. However, this process only happens by chance and there is uncertainty. Therefore, there is no obvious law in the impact of urban shrinkage on environmental vitality.
The correlation coefficient values of comprehensive urban vitality score and urban shrinkage score are all close to 0, and the value of p is far beyond the reasonable range. It shows that there is no correlation between urban spatial vitality and urban shrinkage. According to the index system of this research, the spatial vitality corresponds to the infrastructure construction and support capacity of cities. In developing countries, especially China, infrastructure construction and support capacity are constantly improving. Generally, the index corresponding to urban spatial vitality is likely to improve continuously, so it will hardly be affected by urban shrinkage.
5. Conclusions
Urban shrinkage and urban vitality are unavoidable topics in the process of current urbanization, and it is important to study the relationship between them for the future urban development. In this study, 34 cities in the three northeastern provinces of China are selected as the research objects, and the statistical data from 2010 to 2018 are used. First, the “two-step diagnostic method” is used to identify the urban shrinkage, and then EWM is used to calculate the annual urban vitality of each city. Finally, the correlation between urban shrinkage and urban vitality is analyzed. The findings of this research are as follows: (1) 61.76% of cities in the three northeastern provinces of China have experienced urban shrinkage. Urban shrinkage has become a regional phenomenon in the three northeastern provinces of China, and it is also an inevitable process in China and even other parts of the world. (2) From 2010 to 2018, the urban vitality of the three northeastern provinces of China was generally steady and rising, and the comprehensive scores of urban vitality show a trend of spatial agglomeration according to the height. Yearly, the urban vitality values of Municipalities with Independent Planning Status under the National Social and Economic Development (Dalian) and provincial capitals have been at a high level for a long time, reflecting the trend of factor flow and the imbalance of internal development of the region. (3) There is a significant positive correlation between urban shrinkage and urban vitality in the three northeastern provinces of China. The score of urban shrinkage is negative, and the value of urban vitality is positive, so in general, the lower the degree of urban shrinkage is, the higher the urban vitality is. Urban shrinkage affects the vitality of cities by changing the development factors, and then establishes a correlation to it. (4) The influence of urban shrinkage on each dimension of urban vitality is different according to the different results of correlation coefficient. The correlation between urban shrinkage and economic vitality is the most significant and stable, indicating that the economic level is still an important symbol of urban development; The correlation between urban shrinkage and cultural vitality and environmental vitality is at a medium level, which indicates that the cultural characteristics and environmental carrying capacity cities will be affected by urban shrinkage, but it can also reflect the essence of vitality and get rid of external effects appropriately. The correlation between urban shrinkage and social vitality and spatial vitality is not significant, which indicates that the local differences of urban social structure are obvious, and the sustainable optimization of urban spatial structure in China is difficult to change due to urban shrinkage. The relationships between urban shrinkage and each dimension of urban vitality are different, which affects the level of correlation.
The “two-step diagnostic method” used in this research innovatively gives a system of multi-factor identification of shrinking cities on the basis of fully considering China’s national conditions, which provides a new idea for the research of urban shrinkage identification. At the same time, the significant correlation between urban shrinkage and urban vitality found in this research explains some effects of urban shrinkage to a certain extent, and also reveals the theoretical scientificity of the interactions between urban shrinkage and urban vitality, which can provide a theoretical basis for the corresponding changes in the process of urbanization, and then better guide the high-quality development of cities in the future. Based on this, the three northeastern provinces of China should adhere to strategic determination, and all parts of the world should reach a consensus, aiming at achieving high-quality regional and urban development, reasonably grasping the relationship between urban shrinkage and urban vitality, and guiding their benign interactions.