Main function zoning (MFZ) is the fundamental system of China's territorial development and protection. Through differentiated functional orientation, the core objectives of MFZ are to guide the orderly flow of resources across regions and optimize the spatial pattern of national development. This study evaluates the impacts, their heterogeneities among four types of zones, and underlying mechanisms of MFZ planning on China's population redistribution using county-level data from the three latest national population censuses and causal inference tests through difference-in-differences models. The results show that: The MFZ effects generally align with policy orientation. Post-implementation, optimized development zones, prioritized development zones, main agricultural zones and key ecological zones experienced declining population growth rates, accelerated population agglomeration, accelerated population decline, and growth-to-decline transition, respectively. Using main agricultural zones as reference, the planning reinforced the population concentration advantages of prioritized development zones. The policy effect exhibits dual heterogeneity across regions and hierarchical levels. Population changes in agricultural and ecological zones mostly complied with planning guidance, whereas only 40% of county-level units within prioritized development zones achieved the policy goal of accelerated agglomeration. National-level prioritized development zones demonstrated approximately twice the impact of provincial-level counterparts. Population migration from restricted development zones to urbanized areas predominantly occurred through cross-regional migration rather than intra-prefecture movements, making the policy goal of "concentrated equilibrium" within prefecture-level cities difficult to achieve. The planning promoted shifts in influencing factors of population redistribution within each type of MFZ. The diminished role of secondary industries and enhanced influence of tertiary sectors in optimized zones, along with weakened economic drivers in ecological zones, aligned with planning objectives. However, industrialization in prioritized development zones failed to significantly boost population agglomeration, while agricultural zones remained profoundly influenced by industrialization and economic development, both deviating from intended planning orientations. The findings suggest that the new-round planning could moderately concentrate urbanized area layouts, clarify development sequences for prioritized development zones, and implement more targeted differentiated governance requirements for restricted development zones.

Ecological resilience refers to an urban agglomeration's ability to resist, adapt, and recover from external disturbances. Enhancing ecological resilience is crucial for promoting high-quality development in the modern era. However, few studies have evaluated the ecological resilience of urban agglomerations from the perspective of human-land interactions or explored its evolutionary mechanism. This study assesses the interannual variation of ecological resilience in the middle reaches of the Yangtze River urban agglomeration, focusing on resistance, adaptation, and recovery. The Least Squares Structural Equation Model is employed to analyze the impact degree and pathways through which human-land interactions affect ecological resilience. The results indicate that from 2000 to 2020, resistance, adaptability, and recoverability exhibited fluctuating trends over time and an unbalanced spatial distribution. Ecological resilience initially decreased but later improved, with significant spatial heterogeneity, forming a "higher in the southeast and lower in the northwest" pattern. Natural environment improvement (coefficient: 0.42) and regional policies (coefficient: 0.18) had significant positive direct effects on ecological resilience, while urbanization exerted a significant negative effect (coefficient: -0.26). Although green innovation had no significant direct effect, it exhibited significant indirect influence, with the most significant pathway being green innovation→regional policy→natural environment→ecological resilience (coefficient: 0.18). This study enhances our understanding of how the natural environment, green innovation, and regional policies shape ecological resilience, providing a scientific reference for urban agglomeration development that fosters harmony between humans and nature.

Comprehensive scientific expeditions rely on scientific instruments, paradigms, and technological methods to conduct multidisciplinary analyses of surface conditions, resource endowments, and their dynamic changes and mechanisms, serving major national (regional) strategic needs. Since the founding of the People's Republic of China in 1949, successive comprehensive scientific expeditions have played a significant role in frontier development, ecological environment governance, and national economic development. In the new era, comprehensive scientific expeditions must clarify regional resource and environmental conditions and their changes, fill knowledge gaps in related fields, and support national and regional development and strategic requirements. The development of new technologies and equipment, such as low-orbit satellite constellations, artificial intelligence, and unmanned monitoring, provides important opportunities for comprehensive scientific expeditions in the new era. To advance comprehensive scientific expeditions in the new era, it is essential to fully utilize new technologies, equipment, and methods for innovate expedition paradigms. Guided by national strategic needs, expedition tasks should be organized, which can achieve large-scale, high-frequency, and high-precision investigations of geographical resource elements, filling knowledge gaps in border areas, underground spaces, and deep-sea zones. Based on the regional differentiation of China's natural and human geographical environments, comprehensive scientific expeditions should be conducted in key domestic regions. Focusing on the six major economic corridors of the Belt and Road Initiative and key maritime areas, global comprehensive scientific expeditions should be carried out to promote the building of a community with a shared future for mankind.

This study utilizes emerging hotspot analysis to explore the spatio-temporal trends of vegetation optical depth (VOD) observed in Ku, X, and C microwave bands over China from 2002 to 2017. Furthermore, it analyzes the impacts of anthropogenic activities, represented by land use change, on the spatial and temporal changes in VOD, and employs Partial Least Squares Structural Equation Model to quantitatively assess the climatic effects on VOD changes. Overall, VOD exhibits a southeast-to-northwest gradient over China, with central and southern regions identified as VOD hotspots, while Xinjiang and the central Inner Mongolia Plateau are identified as VOD cold spots. Regions with consistent emerging hotspot analysis results across the three bands demonstrate a "greening" phenomenon in sparsely-vegetated regions nationwide. Additionally, the association between land use change and emerging hotspots reveals strong impacts of human activities on VOD variations. Specifically, persistent and intensified VOD hotspots predominantly correspond to scenarios where grassland is converted to forest. Attribution of VOD changes using Partial Least Squares Structural Equation Modeling indicates that, in the humid zone, where hydrothermal conditions are favorable and soil moisture is abundant, further increases in temperature and precipitation may inhibit vegetation growth. In contrast, in the arid zone, the inhibitory effect of temperature is less prominent. In the Tibetan Plateau, increases in both temperature and precipitation will promote vegetation growth. The insights from this study are expected to provide scientific support for monitoring ecosystem changes, uncovering their driving forces, and assessing the effectiveness of ecological measures.

Rural areal system is a multidimensional object of rural revitalization in the new era, and its complexity and dynamics require a breakthrough in single-domain thinking. Through the in-depth fusion of system science theories, multi-source data-driven technical methods and sustainable transformation paths, the full-chain governance of system diagnosis-scenario simulation-precise policy implementation should be carried out. Based on the scientific theory of human-land system and the multi-scale analysis paradigm of geography, this paper explores the "element-structure-function" cascade analysis system of rural areal system, analyzes the scientific connotation of rural areal system and rural revitalization, clarifies the multi-scale evolution law and transformation mechanism of rural areal system, develops rural areal system development status assessment and scenario simulation technology, and sorts out and proposes a "three-device" (diagnostic device, detector, simulator) platform framework for the transformation mechanism and simulation of rural areal system. By innovating multimodal spatiotemporal data fusion and intelligent interpretation methods, it can break through the technical bottleneck of quantitative inversion of rural areal system elements, establish a multi-factor collaborative observation indicator system and a data sharing application platform, reveal the spatial pattern of rural transformation under different development paths, and explore and create "three major systems", including a theoretical system of rural areal system with multi-dimensional interaction of nature-society-technology, a technical system of cross-platform coordinated observation of rural areal system, and a system of standards and norms for the scientific path of rural revitalization and its management. The findings will help to achieve the systematization of coordinated observation and scenario simulation of multi-source heterogeneous data in rural areal system, and provide theoretical guidance and technical support for the scientific formulation of rural revitalization plans and the comprehensive promotion of rural revitalization strategic decisions. Additionally, focusing on the current trend of technological progress, modern geography should connect with the international scientific frontier and national strategic needs, and take the system integration of geographic science-technology-engineering-practice (Geo-STEP) as the core to promote the transition of rural areal system research from "problem explanation" to "future design" and "scientific governance".

Foreign aid is a tool of U.S. foreign policy and provides a window into U.S. national strategy. In the era marked by frequent local conflicts and global turmoil, delving the motives of U.S. aid can enhance our comprehension of U.S. national strategic objectives. Utilizing U.S. aid data from 2000 to 2019, this paper examines the spatial evolution patterns in U.S. aid and its driving paths, considering altruistic, egoistic, and utilitarian motives. This analysis is conducted using GIS spatial analysis and Fuzzy-Set Qualitative Comparative Analysis (fsQCA). The results show that: (1) Total U.S. aid exhibits a basic trend of initial growth followed by stabilization, with military security aid and economic development aid as the primary categories of U.S. aid. (2) There are significant spatial and temporal differences in the distribution of U.S. aid. The Middle East and North Africa region has been a long-standing aid priority but is trending downwards, with an emphasis on military security aid, economic development aid, and humanitarian assistance. Sub-Saharan African countries have emerged as new hubs for U.S. aid, with primary focuses on social sector aid, economic development aid, and humanitarian aid. Meanwhile, other regions have seen diminishing amounts of U.S. aid. (3) The key drivers of U.S. aid have expanded from the level of economic development and U.S. exports to geostrategic, political relations and institutional quality factors, with an overall trend of a gradual shift from being driven by economic interests to geopolitical interests. This may be related to the eastward shift of the U.S. strategic centre of gravity. In terms of specific types of aid, economic development aid, social sector aid and humanitarian aid are economic interest-driven, military security aid is geopolitical interest-driven, and democratic political aid is democratic value-driven. The different types of aid serve different foreign policy objectives and together constitute a tool for the U.S. to pursue its political and economic interests. This paper can provide some reference for China's foreign policy making.

As an important aspect of the notion that "spatial is special", spatial heterogeneity has been a central topic of geospatial analytics. It is also closely related to the methodological tradition of geography and replicability of geographic research. The emergence of fine-grained big geospatial data and the development of Geospatial Artificial Intelligence (GeoAI) have brought new opportunities and challenges to spatial heterogeneity modeling. Spatial heterogeneity may refer to (1) values of geographic variables; and (2) associations, or the generation process of geographic variables, which correspond to data and process heterogeneity, respectively. Moreover, the specification of spatial heterogeneity may be categorized as continuous and discrete. Based on the dichotomies above, we summarize the main scenarios of spatial heterogeneity modeling and review corresponding methods: (1) homogeneity-based regionalization; (2) local spatial regression; and (3) spatial regime regression. In particular, we discuss approaches to delineate spatial regimes in an endogenous manner. We also review related methodological advances in GeoAI, where the principle of spatial heterogeneity is reflected in the design of neural network models. Finally, we point out several potential directions for future research. As emerging directions in spatial heterogeneity modeling, spatial regime regression and GeoAI methods need more attention from researchers.

Alluvial fans are common fan-shaped depositional landforms that develop at the outlets of mountain rivers or gullies. Mature and stable alluvial fans are important areas for both human habitation and production in mountainous regions, but they also pose potential hazards associated with flash floods and debris flows. Research on alluvial fans enhances our understanding of regional environmental dynamics and geomorphic evolution, as well as contributes to the mitigation of flood and debris-flow hazards. Therefore, it holds significant scientific value and practical importance. Although considerable research has been conducted on alluvial fans, both domestically and internationally, in recent decades, much of it has focused on geomorphology (morphometry), sedimentary history and characteristics, and historical environmental reconstruction (or inversion). Investigations into the mechanisms of fan development and their geomorphic effects remain relatively underexplored. This review systematically summarizes the key advancements in the research on the dynamic processes, mechanisms, and morphodynamics of alluvial fan development. We first provide an overview of current technical approaches applied in the study of alluvial fans, including field investigations and model experiments. Then, we summarize four critical aspects of fan dynamics processes and development mechanisms: primary and secondary processes; mechanisms of flow channel avulsion; interactions between tributary and main rivers; and the impact of alluvial fan development on sediment production, transport, and geomorphic processes. Finally, we discuss several areas that require further attention in future research. Currently, field observations and monitoring of the dynamic processes of alluvial fan development are inadequate. As an essential complement to post-event field surveys and experimental model research, there is an urgent need to enhance field observations in order to expand and deepen our understanding of alluvial fan development mechanisms. This will promote scientific insights into sediment dynamics and geomorphic processes within regional river systems.

Based on the diverse nexus between humans and nature, exploring innovative pathways and regional models for rural revitalization stands as a strategic cornerstone and a cutting-edge focus within rural studies. Following a systematical review on the shift of rural development paradigms, we in this paper propose an innovative pathway of rural neo-endogenous development driven by knowledge through the integration of concepts such as social innovation and rural transformation. Essentially, "knowledge-driven" can be understood as a process-based innovation, wherein various stakeholders participate in the generation, dissemination, feedback, and regeneration of scientific knowledge and local wisdom. This process ultimately precipitates shifts in behaviors and attitudes of both local and extra-local actors, thereby giving rise to collective insights and solutions for rural development. Regarding the functioning mechanisms, "knowledge-driven" typically facilitates the iteration of technological paths for rural development via four interconnected means: constructing novel discourses for rural transformation, empowering local communities, forging connections between local and extra-localities, and innovating rural governance. In practice implementation, "knowledge-driven" engages multiple stakeholders and unfolds across three sequential stages, they are, knowledge/experimentation searching, diffusion and expression of interest, collective learning and co-ordination. In conclusion, we contend that transcending the urban-centric "core-periphery" mindset, broadening the initial impetus and the cohort of pioneer actors, and streamlining the channel from "niche innovation" to "collective learning" hold significant promise for expediting the comprehensive revitalization of rural areas.

A key approach to improving the predictive capability of territorial space planning is to effectively analyze the common challenges and governance experiences of pioneering countries. China serves as a notable example, with its increasing emphasis on integrating rational evolution of territories into spatial planning. In this study, we examined the spatiotemporal structure of Japan's territorial space, spatial transformation, and the spatial and temporal evolution of spatial conflicts from 1976 to 2021 on a national scale. We also simulated the future spatial evolution of Japan's territorial space based on the identification of the key driving factors. The results reveal the following: (1) Over the past 45 years, approximately one-quarter of Japan's territorial space has undergone structural transformation. Considerable urban space expansion and continuous ecological environment optimization have been accompanied by a marked decline in agricultural space and food production. This has created substantial food security challenges due to the degradation of agricultural production capacity. Concentration of the population in economically developed plains and topographically flat bay areas has exacerbated conflicts.(2) Japan's territorial space evolution exhibits distinct stages. Although national economic fluctuations and demographic changes do not substantially affect the overall trajectory of territorial space evolution, they can influence the rate and process of evolution. At the late stage of urbanization, the driving forces of spatial evolution are expected to be more concentrated on demographic, economic, and natural background factors. (3) Simulation results across various scenarios suggest no major structural changes in Japan's future territorial space pattern. Agricultural areas will continue to be encroached upon, exacerbating the national food security crisis as the challenges of rural depopulation and aging population deepen. In the next 10 to 15 years, Japan may form a world-class mega-aging urban agglomeration by linking the three major metropolitan areas of Tokyo, Nagoya, and Kansai.

The integration of large-scale Low Earth Orbit satellite constellations (hereinafter referred to as "LEO constellations") and artificial intelligence (AI) technology presents a historic opportunity for a paradigm shift in geography research, heralding a new era for geography to evolve from qualitative geography, quantitative geography, and digital geography into the "LEO constellation-AI-driven Geography". Under this framework, future geographic research can rely on the high spatio-temporal resolution monitoring data provided by LEO constellations to accurately capture the high-frequency dynamic changes of geographic elements at multiple scales, particularly at the global scale. By coupling physical models with AI, it becomes feasible to conduct simulation experiments on the complex interactions between natural and human elements, system states, and interface changes. This will facilitate a deeper understanding of core geographic issues such as variable coupling, multi-process cascading effects, and teleconnection mechanisms. To propel "LEO constellation-AI-driven Geography", there is an urgent need to establish a new-generation data acquisition and sharing platform relying on LEO constellation, seamlessly creating a "dynamic map" of global geographic resources and elements. Additionally, a geographic process simulator that couples physical models and AI needs to be developed to intelligently simulate and predict changes and impacts of geographic elements and landscapes.

Runoff observation uncertainty is one of the key unresolved issues in the field of hydrology. Current studies mainly focus on the uncertainty sources and their impacts, but the effects of observation uncertainty on changes of entire flow regime characteristics are still rare. This study collects daily runoff observation series from 1971 to 2020 at five hydrological stations in the water conservation zone of the Yellow River (Huangheyan, Tangnaihai, and Lanzhou stations in the Yellow River Source Region, Xianyang Station in the Weihe River, and Heishiguan Station in the Yiluo River). Changes in 16 metrics from five main flow regime characteristics (magnitude, frequency of events, variability, duration, and timing) are detected by the trend tests, and the effects of observation uncertainty on trends of flow regime metrics are evaluated by adopting a normal distribution error model and some metrics, i.e., the uncertainty width, significance change rate of slopes, coefficient of variation, and degree of deviation. Results showed that: (1) At all the stations, flow regimes showed significant increases in the low flow magnitude, and significant decreases in the high and average flow magnitude, variability and duration. At the Heishiguan Station, the magnitude, variability and duration metrics significantly decreased, while the frequency metrics significantly increased. At the Xianyang Station, the low flow magnitude and timing metrics significantly increased, while the high flow magnitude, frequency and variability metrics significantly decreased metrics. In the Yellow River Source Region, the low flow magnitude and high flow timing metrics significantly increased, while the low flow frequency, high flow magnitude and variability metrics significantly decreased. (2) Observation uncertainty considerably affected the trend changes of 28.75% of total flow regime metrics at all the five stations. Among these, the trends of 11.25% of total metrics changed from significance to insignificance, and those of 17.5% of total metrics changed from insignificance to significance. For the rest metrics, the trends remained the same, i.e., significant trends (18.75%) and insignificant trends (52.50%). (3) Observation uncertainty had the greatest impacts on frequency metrics, especially at the Xianyang Station, followed by the duration, variability and timing metrics. The magnitude metrics were impacted least.

This paper reviews the social background of "pole-axis system" theory and the "T-shaped" land development and economic layout framework in China, especially the objective conditions that the country cannot implement another "strategic shift" of national development priorities, and the academic contribution of economic geography serving to national strategic development, as well as some concepts, ideas, knowledge and methods to achieve this goal. According to the significance and the scholars' comments of this theory and model in national practice, this paper describes the growth course and academic responsibility of an economic geographer to inspire the academic community to uphold the rigorous attitude of seeking truth from facts to make greater contributions to the construction of socialism with Chinese characteristics in the new era.

To accurately grasp and effectively coordinate the strategic goals of the great rejuvenation of the Chinese nation and the unprecedented global transformations in a century, while enhancing the country's cultural soft power and the influence of Chinese culture, and promoting the construction of a new form of human civilization, the Chinese nation objectively needs to establish a strategic space that supports the inheritance and innovation of Chinese civilization. This strategic space will serve as a cultural landmark for realizing the great rejuvenation of the Chinese nation through Chinese-style modernization. To achieve this, we develop a construction index system for the strategic space of Chinese civilization inheritance and innovation by repeatedly examining China's regional development and historical and cultural territory. The index system comprehensively incorporates factors such as historical and cultural inheritance, rural revitalization, ethnic diversity, and ecological protection and diversity across five dimensions: history, geography, culture, society, and ecology. At the national district/county level, the strategic space for the Chinese civilization inheritance and innovation is divided into infrastructure construction area, key construction area, priority construction area, and core construction area based on the comprehensive evaluation results. The evaluation results reveal that the strategic space has formed a core area around Shaanxi and a southern core area around Guizhou. The construction conception of the strategic space for the Chinese civilization inheritance and innovation and its division provides strategic support for advancing the great rejuvenation of the Chinese nation and facilitating Chinese-style modernization. Additionally, it plays a significant role in preserving the Chinese spirit and promoting rural revitalization as well as coordinated urban-rural development.

Sustainable development is a significant scientific issue of global concern. Geography, as a comprehensive discipline focusing on the coupled relationship between human activities and the natural environment, provides systematic research and solutions for achieving the United Nations Sustainable Development Goals (SDGs). However, there is currently a lack of comprehensive reviews. This paper summarizes the theoretical framework and research progress of Geography supporting the SDGs and explores its future key research areas. This article indicates that: (1) Geography, in conducting integrated research on human-nature systems and serving regional and global sustainable development processes, has innovatively proposed and developed theoretical frameworks such as social-ecological systems, pattern-process-service-sustainability, metacoupling, and Classification-Coordination-Collaboration. These research frameworks include elements of human-environment system interconnections, process coupling, spatial coupling, and systematic regulation oriented towards SDGs, forming a comprehensive theoretical framework supporting sustainable development research in Geography, also referred to as "sustainable geography theoretical framework". (2) Geography has made positive progress in supporting the United Nations SDGs research in areas such as multi-source data acquisition, localization of indicator systems and multi-scale progress assessment, analysis of inter-target linkage mechanisms, and SDG achievement pathways. Geography provides important theoretical and methodological support for SDG research. (3) Geography and sustainable development-related research mainly focus on climate-ecological crisis response, sustainable utilization of food-energy-water resources, regional development and planning, human well-being and social governance, and the construction of SDG assessment indicators and databases. (4) In future research, there is a need to innovate and develop sub-disciplines of Sustainable Geography, optimize the construction of SDGs indicator systems, develop SDGs assessment and decision-making models, strengthen artificial intelligence geography, deepen research on human-nature system coupling, and promote regional and global sustainable development in the process of advancing innovation in the discipline of Geography.

The physical geography and hydroclimatic conditions in the arid region of in northwestern China leading to diverse flood-generation mechanisms. Under the influence of global and regional climate change, the spatiotemporal variation of floods and flood-generation mechanism in this region is still unclear and restricts flood prevention and mitigation and the implementation of the Belt and Road Initiative in the major regions. Based on the series of the annual maximum flood peak discharge in 58 river basins in the study area from 1961 to 2017, we analyzed and revealed the mechanisms, spatial distribution and interannual variation characteristics of flood in the basin in the past 60 years based on statistical tests and machine learning approaches. The results show that the frequency of extreme floods and the annual maximum flood peak discharge magnitude are increasing, with the maximum increase in the frequency of extreme floods at about 0.84 times/10 years, and the maximum increase in the annual maximum flood peak discharge magnitude at about 29%/10 years compared with the multi-year average, and the largest increase is mainly observed in the eastern Tianshan Mountains and the Qilian Mountains. There are three main flood generation mechanisms, i.e., rain (R), snow (S) and mix (M), the frequency of R and M floods increased significantly, while the frequency of S floods decreased. The contribution of flood mechanisms transformation to the increase of annual maximum flood peak discharge magnitude can reach up to 38%, which is significantly higher than the contribution of a single hydrometeorological factor such as precipitation. The results of this study emphasize the importance of attributing and predicting the changes of flood characteristics in geographically complex region from the perspective of flood mechanisms. Engineering hydrological design in the changing environment also needs to consider the influence of the heterogeneity of flood samples caused by different flood mechanisms on the flood frequency analysis, so as to provide scientific support for flood risk management and response in the basin.

With the rapid advancement of science and technology, artificial intelligence (AI) has become a significant force driving scientific development and social progress. In the field of geographical sciences, the application of AI technology is deepening, bringing revolutionary changes to the collection, analysis, and application of big data and spatio-temporal information, and demonstrating innovative and application potential in multiple aspects. This paper systematically reviews the development and application of AI in geographical sciences, providing a detailed introduction to the development trajectories of various AI fields such as machine learning, computer vision, natural language processing, planning systems, and large AI models, as well as their applications in geography. It discusses the problems and challenges of AI applications in geography and provides an outlook on the future development of interdisciplinary research between AI and geographical sciences.

Metropolitan areas are pivotal in driving national economic growth, advancing harmonious regional development, and participating in competitive international collaboration. Consistent with international consensus, China's planning policies define metropolitan areas as a one-hour commuting circle. Simultaneously, these planning protocols particularly highlight the importance of industrial specialization and intercity collaboration, with the objective of developing modern urban agglomerations characterized by a well-defined spatial structure, complementary urban functions, and an integrated industrial division. This study uses the 2017 intercity input-output table analysis to examine patterns of industrial division and functional synergy in Chinese metropolitan areas. The findings are as follows: (1) From the perspective of industrial division and functional synergy, Chinese metropolitan areas can be categorized into four distinct spatial structures: the single-center dispersed structure, the core-periphery structure, the peripheral expansion structure, and the multi-center network structure representing an advanced phase in the spatial evolution of metropolitan areas. (2) The spatial network of industrial chains in Chinese metropolitan areas is predominantly governed by the flow of processing and manufacturing links. There is a substantial gap in the processing and manufacturing links between the Beijing and Tianjin metropolitan areas compared to similar types of metropolitan areas, and there is considerable potential for enhancing the productive service links in the Guangzhou, Chengdu, and Changsha-Zhuzhou-Xiangtan metropolitan areas. (3) The essence of transforming Chinese metropolitan areas into functionally complementary industrial cooperation areas is to further refine the spatial network of the industrial chains, strengthen functional synergy between cities, and encourage spatial integration in the metropolitan areas. (4) Single-center dispersed structure metropolitan areas, including Shijiazhuang, Chengdu, Wuhan, and Changsha-Zhuzhou-Xiangtan should initially transition toward a core-periphery structure. In contrast, peripheral expansion structure metropolitan areas such as Nanjing and Hangzhou metropolitan areas, and core-periphery structure urban agglomerations such as Tianjin, Shenzhen, Guangzhou and Beijing metropolitan areas should progress toward a multi-center network structure.

Waterlogging, water pollution, black and odorous water, and riverine and lacustrine ecological degradation are the main water problems faced by China's cities, which have become one of the key obstacles to the green development of the Yangtze River Economic Belt. In-depth understanding of the evolution of the water system in the process of urban development and the mutual influences between the elements, clarifying the formation mechanism of the urban water problems, and constructing an integrated treatment technology system of the urban water system are the fundamental ways to solve the complex urban water problems. Aiming at the abovementioned urban water problems, this paper summarizes the concepts and characteristics of the urban water system from a systematic perspective of the multiple processes coupled with each other in the water cycle and proposes a key technology system for a systematic solution to the urban water problems, which are demonstrated with the treatment examples of the urban agglomeration in the Yangtze River Economic Belt in 2016-2022. The demonstrative applications show that the pumping stations and sponge measures can effectively reduce the severely inundated area of Wuhan city in extreme rainfall events and eliminate the waterlogging points in the Chengdu-Chongqing urban agglomeration; the proposed microbial-botanical-hydrodynamic integrated synergistic regulation and control technology can significantly enhance the removal efficiency of the nitrogen and phosphorus level in typical black and odorous water bodies of Wuhan city; the proposed source control-path dissipation-terminal regulation comprehensive ecological treatment system for urban rivers and lakes decreased the water eutrophication level significantly in the Lianghe River basin of Chongqing city; with the implementation of the abovementioned treatment technology system, the green development index of the urban agglomeration in the middle reaches of the Yangtze River increased by an average of 4.8%. This study provides theoretical and technical support of urban water system for the major strategies of the green development of the Yangtze River Economic Belt.

In recent years, the tidal limit of the lower reaches of the Yangtze River has shifted upward, the construction of water-related projects has increased, and the intensity of river bank failure disasters has been on the rise. Previous researchers have found the existence of strong vertical-axial backflow in the bank failure section through field surveys, physical modeling, and numerical simulation, and that there is a strong vertical-axial backflow in the bank failure section; however, the hydrodynamic zone characteristics of the bank-channel interactive zone and the microgeomorphic adaptation mechanism have not been explored. Based on the Doppler acoustic current profiler (ADCP) in the frequent bank failure sections, multibeam system, combined with previous high-resolution underwater topographic data, it is found that the flow velocity and flow direction in the interactive zone of the bank-channel have significant zone characteristics, and according to the backflow strength \alpha, i.e., the longitudinal flow velocity u and its ratio to the transverse flow velocity v, |u/v|, the zone from the channel to the bank is identified into the main stream zone (α<1, u>0), the mixing zone (α≥1), and the near-bank backflow zone (α<1, u<0). The mainstream zone develops large and medium-sized dunes, scour grooves, and scour pits, the mixing zone develops accumulators and small dunes, and the backflow zone develops spines and small dunes; the main stream direct flushing in the mainstream zone and the backflow lateral erosion in the backflow zone are the main driving forces for the development of scouring microgeomorphic type and the development of bank failures, and the high flow velocity gradient in the mixing zone near the main stream zone generates scouring geomorphology, and the remaining part of mixing zone remains a low flow-velocity to make the sediment fall and silt to form the accumulation body. The findings can provide important references for the disaster remediation and near-shore engineering design and monitoring.