1. Introduction
Since the beginning of the twenty-first century, global society has undergone progress and technological advancements, while China has made significant strides in urbanization and industrialization [
1,
2], However, this development has resulted in a progressive degradation of the eco-environmental quality (EEQ) [
3,
4]. It is essential to recognize that social progress and human development are intrinsically linked to the ecological environment [
5]. In the 1990s, the United Nations organized conferences such as the “Conference on Environment and Development” and the “Habitat Conference” [
6], marking the gradual emergence of ecological environment research as a significant area of focus for scholars. Additionally, with societal progress, residents’ economic income and living standards have improved, leading to an inevitable pursuit of a high quality of life, which necessitates a sound ecological environment as a fundamental prerequisite [
7]. Given the growing global awareness of the ecological environment, the evaluation and protection of the ecological environment have become crucial tasks in China’s modernization endeavors.
Since the reform and opening up, China has witnessed unprecedented development across all fields [
8]. However, simultaneously, the ecological environment in China has suffered more severe damage compared to other countries worldwide [
9]. The rapid economic development has come at the expense of ecological degradation, highlighting a disconnect between urbanization development and ecological protection in China, thereby hindering the achievement of sustainable development goals [
10,
11]. This low-coupling phenomenon is a growing concern for both the state and society, particularly as the extent of ecological damage increasingly affects people’s lives. In 2000, China introduced the National Outline of Ecological Environmental Protection [
12], which emphasized the crucial environmental policy of “equal emphasis on pollution prevention and ecological protection,” thereby urging nationwide ecological.
When it comes to assessing EEQ, the OECD (Organization for Economic Cooperation and Development) introduced the “pressure-state-response” (PSR) model in 1990, which was the world’s first recognized EEQ assessment index system [
13]. As scientific progress continues, cross-disciplinary applications are becoming increasingly common. For instance, Mohamed et al. [
14] utilized GIS and RS to examine the interplay between ecological factors, EEQ, and urbanization in the Nile Delta, revealing that rapid urbanization poses significant threats to both ecology and EEQ. Ducrot R et al. [
15] employed 3S technology to analyze the reciprocal relationship between EEQ and urbanization. Sanna [
16] employed principal component analysis (PCA) and cluster analysis to investigate the impact of urbanization development on EEQ in Helsinki. Ja-Hyum Kim et al. [
17] devised a novel modeling approach for evaluating and monitoring urban ecological safety. In the twenty-first century, studies focusing on EEQ evaluation have become increasingly rigorous and comprehensive [
18]. Some scholars have analyzed EEQ from social, economic, and natural perspectives [
19]. For instance, Tan Zifang et al. [
20] constructed an urban ecological suitability index model based on three dimensions (living, production, and environment) and applied it to analyze the EEQ of Changsha city, providing scientific and empirical support for environmental protection policies. Additionally, ecological niche theory has been employed by scholars [
21] to assess EEQ. Bai Jie [
22] conducted a quantitative analysis of the ecological niche in 14 cities in Gansu Province in 2009, employing dynamic cluster analysis. Existing studies on EEQ evaluation have primarily focused on the comprehensive evaluation process, including indicator selection, evaluation principles, and models [
23]. However, there is a notable lack of an internationally accepted standard with high precision for EEQ evaluation [
24].
In conclusion, there is a scarcity of studies on EEQ evaluation in China, and most of the existing studies are limited to specific regions and time periods. Furthermore, there is a dearth of research on continuous, long-term monitoring of EEQ in China since the twenty-first century, which is necessary to comprehensively analyze spatial and temporal changes at a nationwide scale from both horizontal and vertical perspectives. Additionally, many current studies on EEQ evaluation rely on statistical data, which can introduce subjectivity due to the uncertainties associated with different statistical sources. Furthermore, traditional EEQ evaluation methods based on statistical data lack the ability to offer insights into the spatiotemporal changes of future EEQ. Conversely, remote sensing data possesses distinct characteristics of objectivity, scientific rigor, and timeliness. Hence, there is a pressing need to develop a regional EEQ evaluation system that integrates multi-source spatial data, thereby addressing the limitations of current research approaches. This will require a continuous, long-term series of EEQ data for China to analyze trends and spatial variability objectively, scientifically, and reliably. Such data support is crucial for informing China’s ecological environmental protection and pollution prevention policies and mitigating potential ecological risks resulting from urbanization in the future.
Here, based on the evaluation guidelines proposed by the National Environmental Monitoring Centre of China, namely, comprehensive principles, representative principles, scientific principles, comparability principles, and operability principles, we integrated multi-source spatial data to develop a comprehensive evaluation system for EEQ, known as the Modified Remote Sensing Eco-Environmental Quality Index (M-RSEQI). This evaluation system is designed to possess spatial and temporal universality, achieved through the application of the entropy method to ensure objectivity. By utilizing this system, we aim to monitor the continuous, long-term spatial and temporal variations of EEQ across China. The primary objective of this endeavor is to accurately and objectively depict the actual ecological environment of China based on scientific principles.
4. Discussion
In contrast to prior investigations, this study conducted long-term EEQ (Ecological and Environmental Quality) monitoring in the Chinese region using remote sensing data. This approach effectively addresses the limitations inherent in assessments based solely on statistical data [
57]. For instance, Chen et al. [
58] and Lv et al. [
59] employed panel data to evaluate the ecological and environmental quality of China. However, the subjectivity of the statistics and the utilization of data from multiple sources led to controversial findings. By adopting this approach, the inherent constraints associated with assessments relying solely on statistical data are effectively addressed. Furthermore, by utilizing scenario data generated through Earth system models and employing the grid-scale approach proposed in this study, it becomes feasible to forecast future ecosystem quality in China and investigate its evolving attributes. We integrated the Shared Socioeconomic Pathway (SSP) [
60] and Representative Concentration Pathway (RCP) [
61] frameworks to establish three widely employed scenarios. These scenarios were employed to examine the spatial and temporal variations of Ecosystem Environmental Quality (EEQ) in China throughout the 21st century. The analysis was based on comprehensive remote sensing data from multiple sources and data from the Coupled Model Intercomparison Project 6 (CMIP6) model [
62].
Figure 15 illustrates the consistent spatial pattern between the simulated future EEQ for China and historical EEQ, indicating the robust generalizability of the EEQ simulations conducted in this study. In
Figure 15e,f, it can be observed that the average future EEQ for China exhibits a slight upward trend across the three scenarios, but the change is not pronounced. It is noteworthy that under the SSP5-RCP85 scenario, China’s EEQ demonstrates a stable increasing trend (
Figure 15f), implying that the country’s EEQ would remain relatively unaffected by traditional fossil fuel-based pathways. This finding suggests that future human activities would have minimal impact on national EEQ.
However, it is important to note certain considerations within this study. For instance, due to limited ground validation data, it is not possible to provide an accuracy assessment for the entire study area. Furthermore, discrepancies among multiple sources of spatial data introduce some level of uncertainty into the EEQ assessment results, an aspect that was not extensively explored in this study. Nevertheless, this study offers a fresh perspective on global grid-based EEQ monitoring. Moving forward, our research endeavors will focus on investigating EEQ dynamics in rapidly urbanizing countries or regions worldwide, with particular attention to nations such as India and the USA.
5. Conclusion
In conclusion, this research paper aimed to address the lack of comprehensive studies on the evaluation of eco-environmental quality (EEQ) in China, particularly in terms of monitoring its spatial and temporal changes at a national scale. The study highlighted the limitations of existing evaluation methods based on statistical data and proposed a novel approach using remote sensing data to construct an EEQ evaluation system, called the modified remote sensing eco-environmental quality index (M-RSEQI). The main findings of this research provide valuable insights into the EEQ trends in China from 2000 to 2017. The results showed that the EEQ of most regions in China has been improving over the past 18 years, with 60.3% of the areas experiencing an increase in M-RSEQI. However, the overall EEQ of China remained low during this period. The study also analyzed the spatial and temporal changes in the Yellow River Basin, Yangtze River Basin, and four major cities (Beijing, Shanghai, Guangzhou, and Nanjing). The findings revealed variations in the EEQ trends among these regions, with improvements observed in the Yangtze and Yellow River basins. Additionally, the study highlighted the influence of industrial structure and urbanization on the EEQ of Beijing, with a significant reduction followed by a stable trend. Guangzhou exhibited the best EEQ among the four cities, while Shanghai experienced continuous deterioration. Notably, Nanjing’s EEQ showed steady improvement due to extensive efforts in water pollution prevention and control. Overall, this research contributes to the understanding of China’s ecological environment and provides objective, scientific, and reliable data support for ecological protection and pollution prevention policies, thereby helping to mitigate potential ecological risks associated with future urbanization in China.