Based on the analysis of international frontier research, the study of the coupled effects between urbanization and eco-environment represents key research topics in Earth system science and sustainability science over the next decade (Kates et al., 2001; Clark, 2007; Reid et al., 2010). This is because global acceleration of urbanization is posing actual or potential threats to surrounding eco-environments. As early as 1991, the World Health Organization (WHO) identified two major problems facing the world today, which included the deterioration of the natural environment and the rapid decline in the quality of life in urban environments, and the critical impact of urbanization on global environmental changes and its potential to threaten human survival. In 1995, Wally Ndow, the Assistant Secretary-General of the United Nations, issued a warning in “An Urbanizing World” that “Urbanization may provide an unexampled bright prospect for the future, but also may be a knell for an unprecedented calamity, and our future is decided by what we do nowadays.” (Fang et al., 2008; Habitat U, 1996).

In 2005, the International Human Dimensions Programme on Global Environmental Change (IHDP) developed an “Urbanization and Global Environmental Change” research plan. It was the core project of global change research, which focused on studies to strengthen the coupled relationship between urbanization and global environmental change through spatiotemporal scale crossing, spatiotemporal scale comparison and communication between policy makers and the public. The Future Earth (FE) program released in 2012 is a 10-year international research initiative designed to help society respond to the challenges of global change, and to gain key knowledge and explore opportunities for global sustainable transformations. In this project, urbanization is regarded as the most intense human activity on Earth’s surface, and the threshold, risk and critical point of urbanization are the frontier research topics. In April 2014, the committee on New Research Opportunities in the Earth Sciences (NROEC) at the National Research Council (NRC) of the U.S. National Academies highlighted 7 high priority Earth sciences research fields in the next decade in their publication (“New Research Opportunities in the Earth Sciences”). The 6th research topic is “coupled hydrogeomorphic-ecosystem response to natural and anthropogenic change”. The committee believes that humans are altering terrestrial ecosystems through agricultural activities and urbanization (CNROES, 2014) at the National Science Foundation, 2014). In November 2014, the Science and Technology Alliance for Global Sustainability released “Future Earth 2025 Vision”. The building of healthy, resilient and productive cities was one of the 8 key focal challenges proposed in the “Future Earth” research plan.

In the accelerated processes of global urbanization and economic globalization, the rapid expansion of urban agglomerations has become an irresistible trend. With adequate industrial aggregation and economic size, urban agglomerations participate in the global re-division of labor, competition, communication and cooperation, and thus form a strong economic community as well as a community of shared future. According to the United Nations prediction, the proportion of global urban population will exceed 75% of the total population by 2050. Meanwhile, the 40 largest metropolitan areas in the world, which occupy a very small area of the Earth’s surface, are projected to contain 18% of the world’s population. These areas will also participate in 66% of the global economic activities and account for approximately 85% of technological innovations. Additionally, it was stated in the latest World City Report that the world’s metropolitan areas are gradually growing even larger into mega-metropolitan areas and mega-urban agglomerations. It is therefore clear that in the era of globalization and informatization, mega-urban agglomerations, the hub for China’s entry into the world and the portal for the world’s entry into China, heavily influence China’s international competitiveness, and will affect the new pattern of global politics and economics in the 21st century. Compared to the most developed mega-urban agglomerations in the world, such as the Atlantic coast region in the northeastern United States, the Great Lakes area of the United States, northwestern Europe, along the Pacific coast of Japan and the London agglomeration in the United Kingdom, the level of development, and the degree of resources and environmental protection in China’s mega-urban agglomerations are relatively low. China’s mega-urban agglomerations are also regions with the most severe haze pollution and other environmental pollutants. This is due to comparatively lower regional economic gross than the most developed mega-urban agglomerations, and heavy environmental pollution and serious ecological problems. As such, it is necessary to reveal the interactive promotional and coercing relationships between urbanization and the eco-environment in China’s mega-urban agglomerations from an international perspective. Subsequently, this will provide scientific support for resources and eco-environmental protection in the development of healthy and productive agglomerations.

In regard to national strategic needs, the first Central Urbanization Work Conference held in December 2013 and the “National New-type Urbanization Plan (2014-2020)” released in March 2014 both stated that urban agglomerations are the main regions for promoting new types of urbanization. Both the plans, “11th Five-Year Plan” (2006-2010) and “12th Five-Year Plan” (2011-2015), also emphasized that urban agglomerations are the main regions for advancing new urbanization. Moreover, the 17th and 18th National Congress of the Communist Party of China has considered urban agglomerations as the new economic growth core for over a decade, and clearly reinforced that the size and layout of an urban agglomeration should be determined on the basis of appropriate scientific planning and match its resources and environmental carrying capacity. In the “National New-type Urbanization Plan (2014-2020)”, urban agglomeration was mentioned 50 times. According to available statistics, the total area currently comprising China’s urban agglomerations accounts for only 20% of the total area in China. However, 60% population, 80% economic gross, 70% fixed asset investments and 98% foreign capitals of the entire country are concentrated in these regions. The five national mega-urban agglomerations in the Yangtze River Delta, Pearl River Delta, Beijing-Tianjin-Hebei, middle reaches of Yangtze River and Chengdu-Chongqing regions only comprise 9.05% of the total area, while they collectively account for 45% urban population, 50% economic gross and 60% foreign capitals of the entire country. Thus, mega-urban agglomerations are the main regions of China’s new urbanization and core regions of domestic economic development, and as such, these regions will determine the future of new urbanizations and lead economic development in China (Fang, 2014b).

Regarding practical problems and in the context of long-term extensive economic development patterns, mega-urban agglomerations are and also will be the most active and the highest potential areas of current and future economic developments in China. On the contrary, they are also areas that are extremely sensitive and severely affected by highly concentrated and intensified eco-environmental problems. According to the available statistics, industrial wastewater discharges, industrial waste gas emissions and industrial solid waste productions in China’s agglomerations are all greater than 67% of the domestic totals. From the facts stated above, it is clear that although urban agglomerations account for over 75% of total domestic economic outputs, they also produce over 75% of the total pollution outputs, which consequently overload the environments of the agglomerations. Large areas of haze pollution have frequently covered all the urban agglomerations in the eastern coastal and northeastern China, which reflect the emerging issue of environmental pollution in urban agglomerations (Liu et al., 2017). In particular, mega-urban agglomerations are exhibiting the “four-high and four-low” problems and have become sensitive and problematic regions with pronounced urban and eco-environmental problems. “Four-high” refers to unsustainable high-density aggregation, high-speed expansion, high-intensity pollution and high-risk threats (Wu et al., 2015; Chauvin et al., 2017). “Four-low” refers to the low level of resources and environmental protection, low level of development, low compact level and low input-output efficiencies (Fang et al., 2008; Fang and Guan, 2011; Fang and Liu, 2011). In the process of selection and incubation of urban agglomerations, a disregard for resources and eco-environmental carrying capacity has been a persistent issue. Meanwhile, some urban issues need to be urgently addressed such as the unscientific planning and expansion, inclusion of cities that do not meet the inclusion standard and simply grouping cities together to form an agglomeration (Fang, 2015).

From the overview of the current domestic and foreign research on the interactive coupling mechanisms of urbanization and the eco-environment, and the effect of urbanization on resources and environmental protection in urban agglomerations, it is apparent that current research focus is on the resources and ecological issues induced by agglomerations aggregated at a high density (Fang et al., 2016). In addition, theoretical studies to investigate the interaction between high-density agglomerations and resources and environment have gradually garnered attention from researchers. Meanwhile, field studies on the impact of high-density agglomerations on the eco-environment and its systemic regulations have been carried out in some areas (Hummel et al., 2013; Cao et al., 2017). Moreover, quantitative studies aimed at quantifying the resources and environmental carrying capacity in urban agglomerations aggregated at high density have just started. Lastly, research on the coordinated development of industrial aggregates and the eco-environment in urban agglomerations has gradually drawn interest from researchers. However, in the overview of the current studies on urban agglomerations, the research has primarily focused on its spatial expansion, economic development, spatial structure and morphology. Not much has been done to investigate the coupling mechanisms of urbanization and the eco-environment in urban agglomerations, and the systemic regulations to protect resource and environmental dynamics. Moreover, the depth of these studies was not sufficient (Liu et al., 2007).

In regard to discipline development, mega-cities and mega-urban agglomerations have been the focus of urban geography following the initiation of globalization. With the accelerated process of urbanization, traditional urban geography is not sufficient to reveal the cross-city, cross-boundary, cross-field, cross-disciplinary and even cross-country characteristics of mega-urban agglomerations. The basic functions of cities have exceeded the traditional social and economic functions, and have started to interact with eco-environments more frequently. A series of complete urban planning cases have taken practical strategies to prioritize the resources and eco-environment carrying capacity based on the principle of “negative planning”. Overall, a new theoretical framework for human geography is urgently needed to promote its development as a discipline, which in return will guide and satisfy the emerging need for urban development.

Our overall aim is to reveal the key control elements and spatiotemporal evolution characteristics of the interactive coercion between urbanization and the eco-environment in mega-urban agglomerations. Using advanced techniques such as remote sensing, GIS and sensor networks, we will perform systems analysis and spatial statistics to investigate the general dynamic characteristics of natural elements (water, soil, energy, ecology, climate and environment) and human elements (population, economy, society, infrastructure, policy, innovation and globalization). In detail, our objective is to reveal the coercion relationships between resources and the eco-environment, and the characteristic index of urbanization. Moreover, we also want to identify the supportive and restrictive effects of regional resources and eco-environmental elements on urbanization. Furthermore, through screening for key control elements, we will unveil their spatiotemporal evolution characteristics and interactive coercing effects on the eco-environment.

(1) To reveal the dynamic evolution characteristics of the coupled system between urbanization and the eco-environment, and of the responding indices in mega-urban agglomerations. At the county scale, we will identify spatiotemporal evolution characteristics of natural and human elements, and of the responding indices (Figure 2). Natural elements include land resource, water resource, energy, ecology and environment. Human elements refer to population, economy, infrastructure, society, innovation and policy. Meanwhile, in order to further reveal the various natural and human coercing effects, we will analyze the natural and human characteristics of agglomerations. Natural characteristics of agglomerations will include severe water and land shortages, severe pollution, high ecological sensitivity and risks, and high PM_2.5 concentrations, while human characteristics of agglomerations will include high-speed economic growth, high-intensity economy, high population density, major regions of urbanization, concentrated domestic and foreign capital invest-ments, concentrated import and export trades and highly accelerated urbanization.

(2) To analyze the spatiotemporal coupling characteristics between urbanization and the eco-environment in mega-urban agglomerations. First, based on the socioeconomic statistics over the years and spatial comparison analytic methods, we will analyze the dynamic change curve of the interactive promotional and coercing relationships of man-water, man-land, man-carbon, man-climate, man-energy, man-housing, man-biology and man-pollution in mega-urban agglomerations. In general, we want to further reveal the spatiotemporal evolution characteristics of the interactive coercion between human-centered urbanization and water-land-biology-centered eco-environments in mega-urban agglomerations. Second, we can elucidate the temporal characteristics in different periods and the spatial heterogeneity patterns of the interactive coercion relationships between urbanization and the eco-environment, which are driven by different factors in mega-urban agglomerations. Third, by applying structural equation modeling, we can quantify the supportive effects of resources and environmental elements on urbanization, and identify the advantageous aspects of resources and the environment, which promote urbanization. Lastly, we can quantitatively recognize the various restrictive effects of spatially different resources and environments on urbanization.

(3) To screen for key control elements in the interactive coercion between urbanization and the eco-environment, and their coercing effects. Based on the long-term socioeconomic data series, and resources and environmental survey data, we will use grey relational analysis, cluster analysis and principal component analysis to identify key internal and external control elements and their thresholds, which will have the most significant impact on the interactive coercion between urbanization and the eco-environment.

We will further identify the interactive coercion of the key internal and external control elements, construct the interactive coupling matrix, analyze the intensity of interactive coercions, quantify the spatiotemporal coercing characteristics of key control elements and reveal the ecological effects of the interactive coercion of key control elements in different urbanized areas, unveil the spatiotemporal evolution characteristics of key control elements and the interactive coerced eco-environmental effect, and provide fast and slow key control elements to regulate the interactive coercing threshold between urbanization and the eco-environment in mega-urban agglomerations and to assess potential risks to resources and the eco-environment during urbanization (Fang and Wang, 2013).

The urbanization system of mega-urban agglomeration includes 7 elements, which are population, economy, infrastructure, society, innovation, policy and globalization, while the eco-environment system includes 6 elements, which are water resource, land resource, energy, ecology, climate and environment. With respect to inter-regional (external) scale, intra-regional (internal) scale, and the scale of local couplings and telecouplings (Fang and Ren, 2017), we want to explore the interactive coercing and coupled relationships between the mega-urban agglomeration system and the ecosystem (Q = {U, C} = {(u₁, u₂, u₃,..., u_i), (c₁, c₂, c₃,..., c_j)}) under the influence of internal and external elements. These relationships can be defined as the dynamic coupled relationships between U_i and C_j, which will reveal the mechanism, stage, type and coupling pattern of the interactive coerced local couplings and telecouplings between the urban agglomeration system and ecosystem in mega-urban agglomerations.

(1) To reveal the mechanism of the interactive coerced local couplings and telecouplings between urbanization and the eco-environment (Figure 3). Our strategy is to use system coupling models such as correlation analysis, geographical weighted regression (GWR), panel cointegration test, vector error correction model (VECM), KSIM, spatial error model, and spatial lag model to analyze the data generated in the process of urbanization and eco-environmental evolution in mega-urban agglomerations over the past 35 years. At the scales of inter-region, intra-region and coupling, we will explore the mechanism of interactive coercion between urbanization and the eco-environment in mega-urban agglomerations under the influence of internal and external natural and human elements. On one hand, we will perform a “one-to-one” bidirectional analysis of the mechanism of interactive coerced local coupling and telecoupling between a single element of urbanization system and a single element of eco-environmental system, and calculate the interactive coupling coefficient of the element U_i of urbanization system to the element C_j of the eco-environmental system. On the other hand, we will conduct a “many-to-many” multidirectional analysis of the local coupling and telecoupling mechanisms of interactive coercion between urbanization and the eco-environment. We will build a coupling equation of urbanization and the eco-environment (UE = f (U_i - C_j); i = 1, 2, 3..., m; j = 1, 2, 3..., n) and draw coupling curves of interactive coercion between the urbanization system and eco-environmental system. Our results should provide a quantitative scientific basis to achieve harmonious man-water, man-land, man-energy, man-climate and man-carbon relationships.

(2) To define the stages and types of interactive coerced local couplings and telecouplings between urbanization and the eco-environment. Based on the study of the interactive coupling mechanisms of single elements and multiple elements, we will construct a model of the dynamic coupling relationships between urbanization and the eco-environment. By using the data generated in the process of urbanization and eco-environmental evolution in mega-urban agglomerations over the past 35 years, we will calculate the coupling degrees of 6 subsystems of the eco-environment and 7 subsystems of urbanization as well as the coupling degree between urbanization and eco-environmental systems. According to the coupling degrees and in reference to the theoretical evolution cycle of the interactive coupling between urbanization and the eco-environment, we can comprehensively evaluate the process, stages and types of couplings between urbanization and the eco-environment in mega-urban agglomerations under the influence of internal and external elements. This evaluation will determine the stages of interactive coercion between urbanization and the eco-environment based on both bidirectional and multidirectional elements, and the types of interactive coercion between urbanization and the eco-environment based on the identification of coupling stages.

(3) To quantitatively reveal the local coupling and telecoupling patterns of the interactive coercion between urbanization and the eco-environment. First, in reference to the research on mechanisms, stages and types of interactive coercion between urbanization and the eco-environment and the characteristics and laws of subsystems such as water resource, land resource, energy, ecology, climate and environment, we can analyze the coupled boosting effect, coupled reducing effect and coupled constant effect of these subsystems to identify the degree of eco-environment satisfaction to the degree of urbanization demand in mega-urban agglomerations. Second, we can also simulate the dynamic fluctuation process of interactive couplings between urbanization and the eco-environment to reveal the mechanism of stochastic fluctuation in interactive couplings between urbanization and the eco-environment (Fang and Qiao, 2005). Third, we can quantitatively develop the adaptive thresholding algorithm and explore the pattern of interactive couplings between urbanization and the eco-environment (Huang and Fang, 2003; Qiao and Fang, 2006). Fourth, using forewarning methods and forewarning signal models, we can forewarn of potential dangers and report warning signs that are present in the coupling process of urbanization and the eco-environment in mega-urban agglomerations. Lastly, we can also quantitatively unveil the coupling fission law, dynamic hierarchy law, stochastic fluctuations law, non-linear synergetic law, threshold value law and forewarning law of local couplings and telecouplings between urbanization and eco-environmental elements (Fang and Yang, 2006).

Based on the analysis of the interactive coercion relationships between urbanization and the eco-environment, we can determine the coupling status of key control elements and the interactive coupling status of multiple elements. In addition, we can also identify the degree of dynamic couplings of interactive coercion and the degree of severity of interactive coercion. Furthermore, we can comprehensively evaluate the risks of interactive coercion and build a risk assessment system to predict the severity of interactive coercion between urbanization and the eco-environment in mega-urban agglomerations.

(1) To determine the coupling status of key control elements. Based on the available data, we can separately construct models of interactive coupling status between different single eco-environmental elements and urbanization, including man-water, man-land, man-energy, man-carbon, man-climate and man-ecology relationship (Fang and Bao, 2007). These models can clarify the mutually beneficial or detrimental relationships between urbanization and resources and the eco-environment, and quantitatively express the degree of coercion, synchronicity and dependency, and estimate the trend of the aforementioned coupling status change.

(2) To determine the integrated interactive coupling statuses of multiple elements. Based on the models of interactive coupling status of single elements, we can further establish integrated models of the interactive coupling statuses between urbanization and eco-environmental elements including water, land, climate, energy and carbon in mega-urban agglomerations, and thus create an integrated system of the interactive coupling statuses between urbanization and the eco-environment. Moreover, through multiple approaches, we can analyze the integrated interactive coupling relationships among multiple elements, and quantify the degrees of integrated couplings, coercion and coordination between urbanization and resources and environment (Fang and Xie, 2010; Bao and Fang, 2006; Fang and Sun, 2005). Three analytical approaches include artificial neural network models to determine the integrated interactive coupling statuses of multiple elements, ensemble empirical mode decomposition (EEMD) to analyze the synchronicity between multiple temporal resolutions and the interactive coupling statuses of multiple elements, and computable general equilibrium (CGE) model to define the inherent relationships between urbanization and resources and environmental elements.

(3) To identify the degree of dynamic coupling and the severity of interactive coercion, and comprehensively evaluate the risk of interactive coercion. We can treat a mega-urban agglomeration as a living organism and view its metabolic processes and the ecosystem services provided by the agglomeration as ‘vital signs’. Combined with the degree of coupling of interactive coercion, the severity and causes of “urban agglomeration diseases” can be determined. Specifically, the exergy analysis theory can be introduced into studies of urban agglomeration metabolism (Fang et al., 2017). The net exergy yield rate (NEYR), environment load rate (ELR) and exergy exchange rate (EER) can be used to represent the vitality, structure and resilience of urban systems, respectively. Additionally, based on the simulation of ecosystem services of urban agglomerations, and the results of supply and demand analysis, as well as the structural and functional eco-thermodynamic indices of urban agglomerations, such as metabolic utility, metabolic efficiency, metabolic intensity, metabolic eco-coercion and metabolic environmental impacts, we can comprehensively assess the severity, duration and future trends, and analyze the causes of “urban agglomeration diseases” by establishing the baseline and threshold.

(4) To establish a risk assessment system of the interactive coercion between urbanization and the eco-environment in mega-urban agglomerations. We can view the interactive coercion between urbanization and the eco-environment as the source of risk in an agglomeration, with both living and non-living characteristics. According to the degree and duration of coercion, we can analyze the degree to which an agglomeration is exposed to the coercion. Moreover, based on the urban metabolic analysis from eco-thermodynamics and the supply and demand status of ecosystem services, we can evaluate the health status as well as the vulnerability and the resilience of an urban system. Furthermore, using the Bayesian statistical method, we can decipher the interactive coercion between urbanization and the eco-environment into different types of risks, including social security, resource security and eco-environmental risks, and calculate the probabilities of these risks. Lastly, according to the magnitude and controllable degree of risks in agglomerations, we can establish a forewarning system for real-time monitoring of health status, and forewarn the signs and risks of “urban agglomeration diseases”, and record the long-term health status of urban agglomerations.

In reference to the results of the spatiotemporal characteristics, local coupling and telecoupling mechanisms and patterns, and risk assessment of the interactive coercion between urbanization and the eco-environment in mega-urban agglomerations, and on the basis of the system dynamics model, we can reconstruct a system dynamics model of the interactive coercion between urbanization and the eco-environment in mega-urban agglomerations with multi-element, multi-scale, multi-scenario, multi-function, multi-module and multi-agent integrations. Moreover, we will validate the aforementioned spatiotemporal coupling dynamics model, and simulate the thresholds and construct the threshold model of interactive coercion between urbanization and the eco-environment. Consequently, we will build a systematic scientific platform for the quantitative study of urbanization in mega-urban agglomerations. Through adjustments and repeated simulation of critical thresholds, the mid-term to long-term multi-scenario scheme for mega-urban agglomerations can be constructed, which will provide a scientific basis for decision-making to achieve coordinated development of urban agglomerations. Moreover, these critical thresholds can serve as reference parameters for decision-making regarding economic and social development goals, the operation of the economy-population-urban agglomeration system, and the degree of resources and environmental protection in the forthcoming developmental processes of mega-urban agglomerations (Tan et al., 2014; Zhang et al., 2016; Wang et al., 2016).

(1) To construct the system functional modules of interactive coercion between urbanization and the eco-environment. Using models of the carrying capacity threshold and the degree of saturation of ecology-production-life space, we can construct 8 different system functional modules, including water resource and eco-environment, land resource, energy and climate, population and urban system, economic globalization and industrial development, construction and investment of urban and rural areas, transport and logistics, and finally, science and technology innovation, and macro policy. In addition, we can study the core variables and the mathematical expression of each module, use nesting principles to organize these functional modules, and construct a conceptual framework for the dynamics model of the interactive coercion between urbanization and the eco-environment in mega-urban agglomerations (Figure 4).

(2) Dynamics analysis of the key control elements in interactive coercion between urbanization and the eco-environment. By means of regression analysis and a macroeconomic model, and using water resource as the key control element, we can construct the functional module of water resource and the eco-environmental system in the presence of interactive coercion between urbanization and the eco-environment. Moreover, using land resource as the key control element, we will adopt cellular automata (CA) and a multi-agent model to construct the functional module of urbanization and land use change. This model can be used to simulate the expansion of constructional land in mega-urban agglomerations based on single-center, bi-center and multi-center schemes, and to acquire the relevant parameters and threshold of the interaction between land use change and urbanization. Furthermore, the Stochastic Impacts by Regression on Population, Affluence and Technology (STIRPAT) model can be used to simulate the spatiotemporal impacts of quantification of pollutants, affluence and technology on urban energy use and carbon emission, and carry out the life cycle analysis (LCA) of mega-urban agglomerations.

(3) To construct the spatiotemporal coupling system dynamics model with multi-element, multi-scale, multi-scenario, multi-function, multi-module and multi-agent integrations. Based on the existing system dynamics model of urbanization, we will consider key eco-environmental elements, such as water resource, land resource and energy, as the key control elements in the urbanization process of mega-urban agglomerations. Through this approach, we can depict the flowchart of the causal relationship and feedback loop of the spatiotemporal coupling system dynamics model of the interactive coercion between urbanization and the eco-environment with multi-element, multi-scale, multi-scenario, multi-function, multi-module and multi-agent integrations, and we can also reconstruct the aforementioned model.

(4) To conduct computational experiments and determine the threshold of interactive couplings between urbanization and the eco-environment. We will conduct a preliminary simulation of the interactive coercion between urbanization and the eco-environment using the spatiotemporal coupling system dynamics model, test the validity of the model, simulate the thresholds and construct a model of the threshold. Additionally, we will also analyze the interactive coercion between urbanization and eco-environment, and the unhealthy status potential of the urban and eco-environmental systems. The model parameters will be modified and simulated repeatedly until the requirements are fulfilled. Moreover, we will nest and integrate modules, and construct a systematic scientific platform for the quantitative study of urbanization in mega-urban agglomerations.

(5) To conduct scenario simulation of the interactive coupling processes and patterns between the urbanization of mega-urban agglomerations and the eco-environment. According to the basic data on mega-urban agglomerations and the goals of counties in the “13th Five-Year Plan” (2016-2020), we will design multiple experimental scenarios, repeat experiments and calculations, and produce a scenario plan of the process of urbanization in mega-urban agglomerations that can adapt to the thresholds, and resources and environmental carrying capacity. In addition, we will be able to a conduct long-term (2030-2050) forecast and simulation in the interactive coercion process between urbanization and the eco-environment through adjustments to coercion thresholds and repeated simulations, which will ultimately form a mid-term and long-term multi-scenario plan for the development of mega-urban agglomerations.

(6) We will adopt a system dynamics model for resources and the environment to construct systems of forewarning indices and forewarning signs for the interactive coercion between urbanization and the eco-environment. In detail, we can determine the contribution rates of forewarning indices as well as simulate the social and economic development goals and the degree of resources and environmental protection in the recent developmental process of mega-urban agglomerations. Additionally, we can determine the degree of unhealthy urbanization caused by the deviation from the forewarning indices of the coercion between the social and economic development goals and the degree of resources and environmental protection. Collectively, the forewarning response system for the interactive coercion between urbanization and the eco-environment in mega-urban agglomerations can provide a scientific basis for government decision-making.

Based on space simulation and GIS technology, we can build an integrated intelligent decision support system for the interactive couplings between urbanization and the eco-environment in mega-urban agglomerations (UDSS). The UDSS has the distinctive features of high intelligence, high visualization ability and high sensitivity (Figure 5). By combing the UDSS with typical research areas, we can simulate the impacts of resources and environmental protection, and the relevant optimized regulations to determine the appropriate population sizes, space and economy in an agglomeration at different stages, and we can also propose a sustainable development model and a highly efficient growth model based on resource restrictions and eco-environmental capacity (Fang et al., 2011b). In this regard, our models should provide a systematic scientific decision-making basis for the promotion of healthy and sustainable development of urban agglomerations.

(1) To implement multi-scale spatiotemporal simulations of the socioeconomic and eco-environmental elements in mega-urban agglomerations. We can obtain information on natural elements (water, land, energy, ecology, climate and environment) in a wide range of spaces by applying spatialization technologies including remote sensing, GIS, sensor networks, spatial distribution information generated from big data, the method of spatial difference and scale conversion of spatial grid, and surface modeling. Moreover, through the spatialization of the data on human elements (population, economy, society, infrastructure, technology innovation, policy and globalization), we can obtain a wide range of continuous spatial information for these elements. Using the above methods, we can achieve standardization of the multi-source data on urbanization elements as well as the spatialization features and the visualized expression of the spatiotemporal dynamics of socioeconomic and eco-environmental elements. Additionally, under the unified spatiotemporal frame, we can integrate various methods of visualized expressions such as spatial graphs, statistical graphs, flow diagrams and three-dimensional (3D) graphs to show the spatial distribution and statistical results of socioeconomic and eco-environmental elements related to urbanization. In addition, simulated results of urbanization under multiple scenarios can also be generated. Combined with space-time prism, we can achieve four-dimensional multi-scale simulations.

(2) To conduct the visualized scenario simulation of the interaction between urbanization and the eco-environment within the restriction of eco-environmental elements. We will adopt methods such as hierarchy decomposition, cooperation correlation and cascade interaction to construct the coupling model library with a self-organization feature by the standardized assembly method, which can provide highly effective model library support for the visualized scenario simulation of the interaction between urbanization and the eco-environment. Moreover, by using asynchronous evolution, cooperative interaction and feedback network, we will discuss the scenario simulation mechanism of dynamic urban development under multiple interactions and feedbacks. Further, we can complete the scenario simulations in the presence of multiple spatiotemporal dynamic restrictions from the complex eco-environmental elements, and the asynchronous development and asynchronous feedbacks from multi-scale cities. Lastly, by means of spatiotemporal scale conversion and process decomposition, we can explore how to achieve coupled restrictive effects of resources and the environment at the multi-temporal and multi-spatial scales, and also how to achieve dynamic visualized scenarios of the evolution and feedback of urbanization elements.

(3) To develop an intelligent decision support system of the interactive coupling between urbanization and the eco-environment. We will construct an intelligent decision support system of the interaction between urbanization and the eco-environment, which will integrate spatialized environmental elements, systematic dynamic simulations and multi-scale optimized decision-making modules. This system will include a four-dimensional simulation module with multiple scales of population, space and economic size, a scenario simulation module with multi-scale interactions and feedbacks, and a module based on the capacity limit of resources and the environment, and sustainable development. Additionally, we also want to achieve accurate estimation of the multi-scale population and economic sizes of mega-urban agglomerations, achieve simulation of the interactive coercion between eco-environment and urbanization at the scales of county, prefectural city, urban agglomeration and province, and generate an optimized model for the development of highly efficient and sustainable urban agglomerations. Finally, we hope to provide a quantitative decision-making platform for the construction of resource-conserving, environmentally-friendly, ecologically-sustainable and intelligent urban agglomerations.