1. Introduction
With the introduction of the concept of green development and the increase in national attention in this concept, how to realize the harmonious coexistence and common development of man and nature has gradually become a serious problem facing the world. Economic development directly reflects the degree of social development, but too fast economic development will inevitably cause ecological damage and resource consumption [
1]. Therefore, the interaction between economic development and ecological conditions has become a research hotspot [
2].
Scholars at home and abroad have conducted various studies on the interactions between economic development and ecology. Research has shown that only through economic and ecological principles, with trends of synergy, interaction, and simultaneous development [
3], will sustainable development be achieved [
4,
5].
The existing research methods mainly analyze the relationship between economy and ecology from two aspects: quantitative and qualitative perspectives. Among them, the Environment Kuzz Curve, the Pressure-State-Response and constructing the corresponding indicator systems according to the actual problem are the main methods to evaluate the relationship of the economic and ecological environments. The Environment Kuzz Curve [
6,
7] analyzes the relationship between the economy and ecology from a qualitative point of view. The curve shows that ecology will first develop a trend of deterioration and then one of improvement with economic growth [
8]. Yu and Lu [
9] proved that the relationship between social economic factors and water environment pollution emissions was in line with the Environmental Kuznetz Curve model and quantified the two relationships using a linear model. However, the Environment Kuzz Curve only considers the trend of ecology with the economy but ignores the feedback effect of ecology on the economy [
10]. The Pressure-State-Response (PSR) improved EKC’s feedback effects between economic and ecology to represent the interaction of them by pressure indicators, status indicators, and response indicators [
11]. It is also commonly used to explain the interaction between economy and ecology [
12]. The method of constructing the corresponding evaluation system according to the actual problem can evaluate the relationship between the economy and ecology from the perspective of quantitative and intuitive angles. It mainly includes the structural equation model [
12], fuzzy analytic hierarchy process [
5], coupling degree and coupling coordination degree models [
13], etc. Among them, coupling degree and coupling coordination degree are two of the most commonly used methods, which can directly and quantitatively evaluate the degree of interaction and coordination relationship of two or more subsystems [
14,
15].
The analysis of inter-system coupling can be used in urban green sustainable development [
16,
17], carbon emissions [
18,
19], regional economic development [
20], land and sea systems [
21], disaster analysis [
22], water environment [
12], “Belt and Road” [
2,
9] and other areas. However, most of these studies only focused on a region or a city, and did not involve surrounding cities, and lacked a holistic analysis. In addition, the above study only used time-point data for analysis, without considering the steady-state situation of the coordinated changes in the study area in the time period.
The Yellow River is the second largest river in China and is the birthplace of the Chinese nation [
23]. The evolution of the relationship changes in the ecological conditions of the Yellow River Basin and economic development had a huge impact on human production and life. Therefore, it is very necessary to explore the coordinated development relationship and evolution process between economic development and ecology in the Yellow River Basin. So, this paper selected the Yellow River Basin as the research object and prefecture-level cities as the data statistics unit to construct an indicator system for economic development and ecological conditions. The study also analyzed the economic development and ecological conditions of the Yellow River Basin from 2000 to 2018, as well as the degree of coupling between the two. The economic development system focused on the output value structure and resource consumption as the main evaluation parameters; the ecological status development system used the ecological structure and ecological quality as the main evaluation parameters.
The overall purpose of this study is to support the decision making in the sustainable development strategy and then provide guidance and suggestions for the ecological security and comprehensive development of the Yellow River Basin. It also provides technical support for managers and policy makers when studying the sustainable development and drawing up related policies for the Yellow River Basin.
4. Discussion
Due to its unique geographic location, the Yellow River Basin faced more severe environmental protection and economic development; therefore, promoting the coordinated development of its economy and ecology was a major issue related to sustainable development in the region. This article aimed to study whether the economic and ecological development of the Yellow River Basin was coordinated. We analyzed the development degree, coupling degree and coupling coordination degree of the economic and ecological development of the Yellow River Basin in the overall, provincial-level and prefecture-level city.
4.1. Differences at Various Scales
We analyzed the development of economic and ecological development, coupling degree, and coupling coordination degree of economic and ecological development. There was a significant difference in time and space.
At the time scale, there was a significant difference in coupling and coupling coordination levels in 2000 to 2018. The coupling degree in 2000–2005 was lightly coupled, and the coupling of 2005–2018 was intensity coupled; the coupling coordination of 2000–2005, 2005–2010, 2010–2015 and 2015–2018 is moderately maladjusted, barely coordinated, primarily coordinated, and barely coordinated (
Table 8). The coupling and coupling coordination level in prefecture-level cities and the provinces also had differences in 2000–2018 (
Figure 11,
Figure 12 and
Figure 14).
There was also a spatial heterogeneity in the coupling and coupling coordination levels on the spatial scale. The levels of coupling and coupling coordination had spatial heterogeneity in the full-stream scale, provincial scale and prefecture-level scale. For example, in 2000–2005, the coupling degree of the entire basin is moderately maladjusted; the coupling of provinces was mainly on the verge of maladjustment and barely coordinated; the prefecture-level cities were mainly moderately maladjusted, mild maladjustment, on the verge of maladjustment and barely coordinated (
Table 8,
Figure 11 and
Figure 13). In summary, the scale of the analysis is inconsistent, and there is spatial heterogeneity in the results [
26].
4.2. Economic and Ecological Development
The change in coupling degree and coupling coordination degree in 2000 to 2018 showed the difference in coupling degree and coupling coordination degree of the economy and ecology. This result is similar to previous studies on the relationship between the economy and the ecological environment. On a long timescale, the coupling degree and coupling coordination of the economy and the ecological environment will gradually increase over time, but there may be a decrease in the later period [
20].
The reason for this is that the ecological and economic development is inconsistent. There were two aspects that caused the difference in ecological and economic development.
First, the support of national policies is responsible for this difference, which made the economy in the study area continue to develop. There is a significant regional difference in economic development [
27], and the difference in economic development in various regions is due to the support of government policies [
26]. In other words, the government’s policy support is the main driving force for economic development. In this regard, the Chinese Government should increase the policy support of economic development, change the unreasonable financial system, and reasonably configure the proportion of the first, second, and third industries.
Second, the relationship between economic development and ecological development was inhibitory. A too fast economic development will inevitably destroy the ecology, and the ecology will restrict the economic development through a series of feedback forms such as natural disasters, environmental pollution, and resource shortages [
28,
29,
30]. However, the ecology had a certain lag in response to the economic system [
31]. In order to make the ecological environment improve and develop and accomplish the coordinated development of economic and ecological environments, we should practice the scientific discussion of China’s “lucid waters and lush mountains are invaluable assets” and strictly implement the Yellow River forbidden fishing policies.
4.3. Experimental Design-Related Issues and Defects
In addition to the cause of the results of the analysis, we also discussed the time period selection and data integration issues in this paper.
First, we considered the time selection problem. In order to analyze the coupling coordination degree of the economy and ecology of the Yellow River Basin, we selected 2000 to 2005, 2005 to 2010, 2010 to 2015 and 2015 to 2018 as the time interval of the analysis. The selection of time interval was due to the five-year change trend over a period of time, which more intuitively reflected the fluctuations in time during the time period, so that the changes were more obvious.
Second, we considered the integration of data. In addition to land use classification data, other parameters were used from 2000–2005, 2005–2010, 2010–2015 and 2015–2018, such as the mean of each time period to express the steady state changes of parameters in the time period. Due to the slowness of the land use classification data and the lag of statistics, we used the 2000, 2005, 2010 and 2015 land use data of the ecological compositions in 2000–2005, 2005–2010, 2010–2015 and 2015–2018 (
Figure 2).
All in all, data lags and the data integration process may bring errors to the results. These is also the limitations of our study.
5. Conclusions
This study combines the coupling degree and coupling coordination model and the coupling coordination of economic development and ecological status. Unlike most of the previous research, this paper introduces economic structural and energy consumption first-level indicators in the system of economic development, introducing ecological structural and ecological quality first-class indicators in the ecological status system. Based on these indicators, we analyzed the time and space evolution of economic development, ecological state and coupling and coupling coordinated degree in the Yellow River Basin from 2000 to 2018. The main research findings are as follows:
- (1)
The economic composition index and the economic development index have showed an upward trend, but the energy consumption index showed a slight downward trend in 2015–2018. This shows that the dependence of future economic development on basic energy consumption is gradually reduced. The economic index rose at an accelerated rate, indicating that the level of economic development and constant improvements, which further promoted the coupling of the economy and ecology.
- (2)
The ecological quality index has continued to rise since 2010, while the ecological state index and ecological composition index showed a downward trend in 2010–2018. It is indicated that ecological quality has continued to improve, but ecological composition still plays a leading role in evaluating the ecological state.
- (3)
As far as the evaluation of the level of economic development and ecological conditions is concerned, the level of economic development is low in the west and high in the east; the level of ecological conditions is high in the west and low in the east. This shows that there are significant regional differences in economic development and ecological status grading.
- (4)
During 2000 to 2018, the economic and ecological coupling state in the Yellow River Basin showed a strong interaction that subsequently slightly weakened. The system of economic development and ecological state have mutually promoted each other.
- (5)
During 2000 to 2015, the coupling coordination degree of the economy and ecology of the Yellow River Basin continuously improved during the study period, but it was reduced in 2015 to 2018. The coupling coordination level experienced moderate maladjustment, mild maladjustment, endangered maladjustment, slight coordination and primary coordination. The decrease in the degree of coupling coordination is due to the uncoordinated development of economic and ecological conditions.
- (6)
The coupling degree and coupling coordination degree of economic and ecological conditions differ between large-scale and small-scale regions, which shows that the coupling degree and coupling coordination degree of different spatial scales present spatial heterogeneity.
In 2000–2018, economic development continued to increase; the ecological condition increased and then reduced due to the effect of ecological composition. The development difference between the economic development system and ecological condition system caused time change differences in coupling and coupling coordination. Due to the difference in research scale, the economic development, ecological status, coupling and coupling coordinated degree is space heterogeneity.
The above results will help the policy makers in the Yellow River Basin formulate appropriate sustainable development measures and establish and maintain the balance between economic development and ecological status.