**1. Introduction**

The shrinking city is a young, crucial issue related to human sustainably development which needs to be given more attention. It is not a new thing, but it is a new problem that needs to be solved urgently. After the industrial revolution, cities grew explosively [1]. Both the number and the size of cities have shown a rapid growth which is unprecedented in human history. Since the 1990s, the urbanization rates of the United Kingdom, the United States, Germany, and France have far exceeded 50% [2–5]. However, at the beginning of the 20th century, some cities in these countries ended their growth process, and a series of problems such as urban population decline, economic recession, industrial imbalance, and a surge in unemployment appeared. For example, Leipzig, Germany, lost more than 100,000 people from 1951 to 1998, accounting for 20% of the total population [6]; Liverpool, the United Kingdom, began to experience a large-scale population decline in the mid-19th century. As of 2008, its population had decreased by 49% compared to 1931 [7]. Similar cases include the city of Hakodate in Japan, Detroit and Pittsburgh in the United States, and Leksa in Finland, etc. These cities all once flourished during the industrialization period, but they have all undergone a historic transformation from prosperity to decline.

The phenomenon of the shrinking city does not only appear in highly urbanized developed countries. In the process of large-scale urbanization, shrinking cities in China have begun to appear. China's urbanization has entered the turning point of the times,

**Citation:** Wang, Y.; Lin, M.; Gao, J.; Zhou, Z. Fading Attraction of the Shrinking City: An Empirical Study from an Urban Resource Perspective.*Sustainability* **2021**, *13*, 11550. https:// doi.org/10.3390/su132011550

Academic Editors: Pierfrancesco De Paola, Francesco Tajani, Marco Locurcio and Felicia Di Liddo

Received: 3 September 2021 Accepted: 11 October 2021 Published: 19 October 2021

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with large cities that cannot be contained on the one hand, and small cities that cannot be supported on the other [2]. Relevant studies have used different statistical calibers to identify and analyze shrinking cities. Due to the differences in the definition and the criteria of a shrinking city, the results obtained by related scholars are not in complete accord. After analyzing the data of the Fifth Census (2000) and the Six Census (2010), Zhang believed that more than 26% of the prefecture-cities and 37% of the county-level cities in China have experienced relative shrinking [3,4]; Long pointed out that between 2000 and 2010, 180 cities in China experienced negative population growth [5]. After analyzing the data of 663 cities in China from 2007 to 2016, Wu found that 84 cities had different degrees of shrinking [6,7]. Although the conclusions obtained by various scholars are different, it should not be ignored that these results show that the phenomenon of urban shrinkage has indeed occurred in China. Furthermore, the number and scale of the shrinking cities are still expanding.

In order to reveal the mechanism of the population loss and the series of problems, the "shrinking city" was formally proposed by scholars [8], and a few scholars have carried out in-depth research on it and achieved a series of fruitful results. As shown in Table 1, de-industrialization, suburbanization, and political system transformation have become the main reasons for the shrinking cities in European and American countries [9,10].


**Table 1.** Influencing factors of the shrinking city.

Due to the late start of urbanization in China, the shrinking city mainly occured in the 21st century, with the data explosion and rapid development of science and technology. Therefore, the phenomenon of the shrinking city in China not only has similar incentives to the developed countries but also has its unique side. The continuous construction and improvement of infrastructures such as transportation networks and telecommunications have greatly increased the flow of the population and resources in China. Besides this, many cities have abolished household registration restrictions, and some cities have provided excellent talent introduction policies to attract talents. The weakening and canceling of the restriction policy and the establishment and strengthening of the encouragemen<sup>t</sup> policy are gradually breaking the shackles of the population flow in China. According to China's national census data, in 2010, 261 million people left their registered places for more than half a year, with 82% of the total migrants being in eastern cities and 18% in being in central and western cities. Since the 21st century, China's population migration has become larger, faster and more frequent.

Urbanization is the process of population and resource agglomeration. In the urbanization process, some cities continue to expand, while others shrink. City shrinkage has many causes, such as economic development, climate, location, political factors and so on [32]. However, to sum up, the final reason is the city's decreased attraction. The gathering of resources accelerates the gathering of the population, and the value creation and consumption demand of the population gathering further promote the re-distribution of resources. Cities with strong "attraction" tend to gather a lot of excellent resources and become the inflow places of population, while cities with weak "attraction" naturally become outflow places. Therefore, we proposed the hypothesis that urban resources are a combination of the ability of cities to compete for external resources and the reflection of the endowment of urban resources. The level of urban resources is closely related to urban shrinkage. The level of urban resources determines the attractiveness of the city, reflecting the direct cause of urban shrinkage. However, few pieces of literature conducted an in-depth analysis of the shrinking city from the urban resource perspective. The objectives in this study are therefore to: (1) establish the URD model to measure the urban resource degree, and (2) to select factors to analyze how they influence the shrinking cities. Given the spillover effect and heterogeneity of the influencing factors, SDM and GTWR were used to conduct a spatial spillover (SSM) and spatial heterogeneity (SHM) analysis of the URD of shrinking cities in northeast China. Finally, policy implications are proposed to provide supports for policy-making.

#### **2. Urban Resource Degree (URD) of the Shrinking Cities**
