1. Introduction
The urbanization rate of the resident population in mainland China has reached 65.22% in 2022 [
1]. Although population migration to cities can provide sufficient manpower, expand the urban scale, and prosper the urban economy, cities are required to develop rapidly and sustainably to adapt to the influx of a large number of people and the rapidly increasing urbanization rate [
2]. However, rapid urban development may not mean high-quality urban development, and even various potential crises in the process of rapid urban development may be encountered [
3,
4]. These crises do not only come from natural disasters, such as the extremely heavy rainstorms and the catastrophic hurricane events [
5,
6] but also come from man-made disasters, such as accidental disasters, public health events, and terrorist attacks [
7,
8,
9]. The occurrence of these crises can disrupt the orderly operation of urban systems and, in severe cases, even destroy systems. Therefore, the idea of building “resilient” cities has emerged [
10].
Resilience refers to the ability of a system to absorb and resist disturbances and maintain or restore the original system in the presence of external disturbances [
11]. From this concept, it is clear that resilience is a measurable ability. If this ability is stronger, the more it can absorb and resist external disturbance and maintain or repair the original system. If the external disturbance exceeds the upper limit of the ability, it will destroy the system. Therefore, the greater the resilience is, the greater the system’s resistance to interference, and the more stable the system will be [
12]. It means that “resilient” cities have a better ability to maintain system stability or rapid recovery. Therefore, academics have begun to explore how to promote “urban resilience” [
13]. Urban resilience represents the ability of cities to resist, maintain and recover from various crises, and the degree of this ability determines the health, stability, and development of urban systems [
14].
As a complex system, any city has a certain ability to maintain the dynamic stability of the system structure and function. It means any city has a certain degree of “resilience” [
15]. The urban resilience will gradually adjust with the development of the city [
16]. Urban resilience is both a comprehensive representation of the resilience degree of each subsystem in a city and a measurable urban capacity value that changes with time dimension [
17]. Through evaluating urban resilience, it is possible to determine the ability of existing cities to resist crises and maintain and recover urban systems. It can also identify which parts of the urban system are not resilient enough so as to promote urban resilience [
18].
This paper attempts to address how to evaluate urban resilience from the perspective of comprehensive evaluation and sub-space evaluation. Based on the sub-space evaluation results, this paper also wants to identify the reasons for the insufficient urban comprehensive resilience and propose appropriate suggestions for improving urban resilience. Therefore, this paper will propose the evaluation index system and evaluation method of urban resilience with reference to the concept of “trio spaces“, using the CRITIC-entropy method and the cloud evaluation model. Taking four sub-provincial cities in Northeast China as examples, we analyze the resilience of each city from 2014 to 2020 and propose suggestions to improve urban resilience according to the shortcomings of urban resilience building.
This paper is divided into five sections.
Section 1 is the introduction of this paper.
Section 2 reviews the literature on the connotation and evaluation of urban resilience.
Section 3 describes the theory and method of this paper.
Section 4 evaluates the urban resilience in four sub-provincial cities in Northeast China and gives the results of urban resilience comprehensive and sub-space evaluation.
Section 5 discusses the results and concludes the study.
5. Discussion and Conclusions
In this paper, under trio spaces, the indicator system of urban resilience evaluation is established from the robustness, efficiency, resourcefulness, redundancy, and adaptation of physical space, societal space, and cyberspace. The evaluation model of urban resilience is established by using the CRITIC-entropy value method and cloud evaluation method. Harbin, Changchun, Shenyang, and Dalian in Northeast China were taken as empirical areas, and their urban resilience was evaluated comprehensively and spatially. The results show that the comprehensive evaluation results of urban resilience of the four cities in Northeast China are at the level of “qualified”, and there is still much room for improvement. The results of the space evaluation not only explain the comprehensive evaluation results but also help this paper to propose suggestions to improve urban resilience.
First, the resilience of physical space and societal space should continue to develop steadily, while the resilience of cyberspace is still the shortcoming of most cities and should be given high priority.
From the evaluation results of sub-spaces, most cities can basically achieve a “qualified” level of resilience in physical space and societal space. Continuous and stable improvement of the resilience of the two spaces will help to improve the comprehensive resilience level. From the results, most urban resilience levels cannot be effectively improved because of the lack of cyberspace resilience building. Therefore, in the era of big data, further improving the cyberspace resilience through digital and intelligent means will help to improve the comprehensive resilience level. Although the development of big data in the world has reached a climax since 2013, and the Chinese government is also laying out the development strategy of big data. It was only after 2016 that the Chinese government began to gradually and comprehensively promote the development and application of big data [
66]. Since the application and promotion of big data in various regions need time and cycles, and there is a regional imbalance in technology development. It means that the enhancement of cyberspace resilience in various regions needs a process. It is the reason for the lower cyberspace resilience compared to physical space resilience and societal space resilience in evaluating the urban resilience of these four Northeastern cities in China from 2014 to 2020.
Second, in the process of urban resilience enhancement, the common enhancement of each space resilience should be highlighted. Especially the synchronization of resilience building in societal space and cyberspace needs to be highlighted, which helps to achieve the balance of resilience building in trio spaces.
It can be seen that the key to urban resilience enhancement is to focus on the balance of resilience building of trio spaces. For example, the resilience building of societal space and cyberspace in Changchun often appears to be in a situation where they are in contrast to each other, which leads to the inability to effectively improve the comprehensive resilience level in Changchun. Therefore, in the process of building the resilience of trio spaces, it is necessary to maintain the simultaneous improvement of each space, which can promote the improvement of the comprehensive resilience level.
Third, fluctuations may occur in the process of improving the resilience of trio spaces, and it is necessary to establish an urban resilience evaluation index system and regularly monitor the urban resilience building. The problems can be found, and program adjustments can be made in time when fluctuations occur.
It is clear that the improvement of urban resilience does not happen overnight but needs to face a long-term and iterative process. For example, the cyberspace resilience of Dalian tends to fall before rising, thus affecting the improvement of the comprehensive resilience level. To stop the decline of the urban resilience level as soon as possible, a reasonable evaluation index system can be established, and the urban resilience building situation can be monitored regularly. Through evaluation and monitoring, the key problems in the trio spaces can be found in time, which is helpful to stop the damage and promote the construction of urban resilience in time.
Finally, if the local government can recognize the importance of urban resilience building, they can guide the construction by formulating local program documents. If the local government can actively absorb the experience of other cities with better resilience building, it will also help to improve the comprehensive level of urban resilience. It is worth noting that although improving urban resilience can help cities enhance their abilities to resist disasters and promote urban development, it is also necessary to highlight the degree of urban resilience and not force the resilience building beyond the law of trio space development. The best urban resilience building plan should be developed according to the development of physical space, societal space, and cyberspace in each city, and the urban resilience building should be steadily promoted.
The innovation of this paper is reflected in the following two aspects. First, this paper explores the issue of urban resilience evaluation based on the theory of trio spaces. It not only clarifies the dimensions of indicator selection more clearly, but also reveals the impact of visible physical space, invisible societal space, and cyberspace on the urban resilience. Second, compared to previous studies using a comprehensive fuzzy evaluation method, the cloud evaluation model used in this paper can also effectively evaluate the urban resilience. It can use cloud maps to intuitively reveal the trend of urban resilience level and whether it is susceptible to the external environmental influences, which is more conducive to providing suggestions on how to maintain and enhance urban resilience and avoid negative impacts of external environment. Overall, the theoretical contribution of this paper is to clarify the relationship between the concept of trio space and urban resilience, laying a theoretical foundation for the construction of an urban resilience evaluation index system. A cloud evaluation model was proposed for urban resilience, providing a model reference for future resilience evaluation. The practical contributions include clarifying the current status of urban resilience in the four cities in Northeast China and identifying the main reasons for the lower resilience. Some suggestions are proposed to enhance resilience from different space perspectives of urban resilience in this paper.
There are also some limitations. First, to ensure the aggregation of cloud drops, this paper refers to the previous literature and sets the He as 0.001. Although it has little impact on the results of urban resilience evaluation, the distribution of urban resilience cloud drops under different He can be considered in the future. Second, the results reveal more about the impact of different spaces on urban resilience but fail to clarify which factors affect the resilience of each subspace. In the future, we should combine the method of cause analysis to clarify the reasons for the impact on the sub-space resilience. This paper explores the level of comprehensive resilience rather than evaluating resilience for a particular disaster. It will also explore urban resilience in the future under the premise of more resilient goals; that is, evaluating urban resilience from different disaster dimensions.