Geography, as part of earth science, is a complicated system composed of multiple disciplines. Interdisciplinary studies are the significant characters of geography. With the rapid development of low-altitude airspace exploitation such as the application of UAV, low-altitude airspace has become a subject of research field of geography. Recently, there are many interdisciplinary studies and integration between geography and aeronautics. However, it is a difficult and innovative task to take the low-altitude airspace as a fixed research object of geography and develop it into a branch of geography named low-altitude airspace geography. In this paper, we consider the low-altitude airspace as a complex giant system, which has two geographical characteristics of synthesis and regionalism. Herewith, low-altitude airspace is a research object of geography in theory, which is the basis of generation of low-altitude airspace geography. The development trend of low-altitude airspace geography is to deeply conduct interdisciplinary studies with aeronautics, physical geography, human geography, information geography. On the basis of analyzing the relationship between low-altitude airspace geography and the above-mentioned disciplines, we tentatively proposed the preliminary layout of the discipline system of low-altitude airspace geography, which is composed of integrated low-altitude airspace geography, departmental low-altitude airspace geography and low-altitude airspace information geography. This paper aims to promote the development of low-altitude geography as a new academic growth point of geography to some extent.

The Hengduan Mountains Region is one of the regions with the most densely distributed and severe flash flood disasters in China. It is also the key area for major engineering projects and beautiful countryside construction in southwest China. However, previous studies have not systematically summarized the development characteristics and formation modes of flash flood disasters in this region, which restricts the development and establishment of flood control theory and technical system in the southwestern mountains. This paper focuses on the physical processes of generation, movement and hazard-formation of flash flood disasters in the Hengduan Mountains. It clarifies the dominant disaster-inducing conditions (multiple humid monsoon circulation conditions, high potential energy conditions and high heterogenous underlying surface conditions) and disaster development characteristics (high spatio-temporal heterogeneity, highly concentrated energy, disaster chain and clustered occurrence) of flash floods in the Hengduan Mountains. Based on the entire processes of flash flood disasters, three major formation modes are summarized: the runoff generation of vegetation-hydrology-soil coupling dominated by high hydraulic gradient in mountainous areas, strong runoff-sediment coupled movement, and serious disaster losses due to high exposure of disaster bearing objects. Finally, based on the issues in previous research, four future research challenges for flash flood disasters in the Hengduan Mountains are proposed. Our work contributes to the development of disaster prevention and reduction research, including basic theoretical system, precise risk assessment of regional disasters, and fine early warning and forecasting of flash floods.

According to the strategic direction of urban-rural integration and rural revitalization, the spatial reconstruction of rural settlement system is the spatial organization foundation of future urban-rural integration development. This paper focused on the hierarchical scale and spatial organization characteristics of the rural settlement system. It comprehensively revealed the evolution process and regional characteristics of rural settlement systems of 111 administrative units in Guangdong province from 1990 to 2020, and discussed their evolutionary mechanism and spatial optimizing and reorganizing regional modes. The results show that: (1) There were significant regional differences in the hierarchical scale distribution of the rural settlement system in Guangdong. The patches of rural settlements show the characteristics of concentric aggregation and distribution centered on the geometric barycenter of each administrative unit. The spatial distribution pattern of the rank cumulative size coefficients of rural settlement system was "high in the southwest, but low in the northeast" and "high in coastal areas, and low in the inland". The decreasing region of the rank cumulative size coefficient was concentrated on the east bank of the Pearl River Estuary and coastal areas of eastern Guangdong, while the increasing region was mainly distributed on the west bank of the Pearl River Estuary. (2) The influencing factors such as natural background, economic development, urbanization development, transportation and location, institutions and policies jointly drove the development and evolution of the rural settlement system. Rural settlement system of urban areas is small in scale in the mature stage of urbanization, which will gradually die out and integrate into the city. Driven by urbanization, industrialization and policies, rural settlement system of suburban areas has experienced survival of the fittest and maintains a stable scale, but the mixed distribution of urban and rural land makes the spatial organization of rural settlements increasingly loose. Driven by the continuous outflow of production factors, exurb rural settlements appear to be "hollowing out". The villagers returning to build new houses and the lack of homestead exit mechanism have led to a continuous and stable growth in rural settlement scale, and their spatial distribution is characterized by more peripheral diffusion. Rural settlement system with poor location in mountainous areas develops slowly under the support of policies, and the aggregation characteristic along the transportation line is significant. (3) Facing the integrated development of urban and rural spaces, four models of spatial optimization and reorganization of rural settlement system are proposed: urban-rural integration development, dual-core-driven development, central place hierarchical system development, and pan-center chain-connecting cluster development.

Population equilibrium development is the valuable guide and ideal pursuit of China's population policy and has significant implications for regional equilibrium development. However, there are still misunderstandings about interpreting population spatial equilibrium, and its scientific connotation requires further explanation and promotion. Population spatial equilibrium gives the meaning of space based on population equilibrium, which can be understood as the spatial equilibrium of population distribution. When other factors remain unchanged, the net migration between regions is zero; that is, the total number of immigrants of each region are equal to its total number of emigrants to achieve the dynamic equilibrium of population distribution among regions. A migration stream will exist between regions in an equilibrium state. Migration and equilibrium can coexist, but the population distribution between regions remains dynamic and stable, and the population spatial distribution structure will not change. Specific conditions cause the inherent stipulation of population spatial equilibrium. The equilibrium point will also change with economic, social, resource, and environmental changes. Equilibrium is a relative concept derived from the instantaneous concept; instantaneous equilibrium is an ideal state in the long term. The population spatial distribution is constantly changing from disequilibrium to equilibrium and from equilibrium to disequilibrium. This paper describes a theoretical model of multi-regional population spatial equilibrium based on the regional wage rate, human climate suitability index, urban crowding degree, and distance. Using the Yangtze River Delta as an example, the study analyzes the equilibrium population spatial distribution under current economic, social, environmental, and population conditions. The study found that the population of the study area is concentrated along the river and the coast, mainly in the south of Jiangsu, along the coast of Hangzhou Bay, and the canal from Nanjing to the north of Jiangsu. By comparing the equilibrium population with the current distribution, the Yangtze River Delta can be divided into quasi-equilibrium, attractive, and repulsive areas. The attractive areas, such as Shanghai, Nanjing, and Hangzhou, have large population agglomeration potential. In contrast, the repulsive areas are mainly located in northern and western Anhui, northern Zhejiang, and other areas close to the quasi-equilibrium area. This suggests that under free migration, the population will further concentrate in the areas of Shanghai, Nanjing, Hangzhou, and southern Jiangsu.

With the increasing global warming over the past three decades, the climatic zones and eco-geographical regions characteristics in China have changed. This study used the climatic data of 641 meteorological stations over the past three decades (1991-2020), as well as the high-precision data of eco-geographical elements to optimize the eco-geographical regions in China. The study updated the map of eco-geographical regionalization in China (2023) and increased the scale to 1:4000000. The new map divided China into 11 temperature zones, 22 dry and wet regions, and 50 natural regions. The results show that compared with eco-geographical regionalization in 2007, the overall pattern of eco-geographical regions in China has not changed significantly over the past three decades, but the boundaries of temperature zones, dry and wet regions, and eco-geographical regions (natural regions) in some areas have changed to some extent. Firstly, the boundary change of temperature zones is more obvious in the east. Particularly, in the middle and lower reaches of the Yangtze River, the northward shift of the temperature zone boundary between the northern subtropical and the mid-subtropical zones is obvious. Secondly, the boundary between dry and wet regions has changed, and that between semi-arid and arid regions in the north of the second-order landform step has shifted slightly to the west. In addition, the boundary between semi-arid and sub-humid regions in the Qinghai-Tibet Plateau has shifted slightly to the southeast, reflecting a slight expansion of the scope of semi-arid regions. Finally, boundary changes in natural regions in some areas vary greatly. This study can provide a macro-regional framework for guiding ecological conservation and restoration in different regions.

Social-Ecological System (SES) is a collection of social subsystems, ecological subsystems, and the interactions between them. It is a common difficulty of cross-multidisciplinary fields to predict the changes in human-earth systems and support the relevant management decisions through clarifying the interaction between the ecological environment and human society. The framework of ecosystem service provides a new perspective for revealing the transmission and the role of various elements in SES. Taking ecosystem service as an entry point, this study follows the context of "Ecological System Supply-Ecological Coupling Human Intervention-Promoting Social Development". And the research progress and trends of existing coupling simulation methods related to SES are summarized. This article argues that in the conduction research of the ecosystem services cascade, the academic cognition has emphasized the "impact of natural ecosystem to social-economic system" rather than the "interaction and feedback mechanisms for ecosystems and social systems". In terms of research content, scholars have trsnsformed their focus from "changes in ecosystems and environmental effects" to "social-economic system and the effect on different groups". The focus of research has shifted from the theoretical inquiry of the "internal mechanism and power mechanism" to the applied practice of "optimization and regulation strategy" among the coupling systems. Future research of SES should strengthen the simulation of social-ecological coupling with equal emphasis on nature and humanities. It is the focus of breakthroughs to comprehensively understand the internal interactions and feedback of complex systems.

Economic globalization has reshaped the world economy's spatial pattern while simultaneously changing the context for developing economic geography theories. This study revisited the changing features of economic globalization and investigated its geographical implications. Next, it summarized the new trends in economic geography studies in response to the changing economic globalization. Lastly, this study proposed a research agenda for domestic economic geography studies by combining the requirements of global trends and national strategies. The main findings include the following: The scale of geographical integration during economic globalization keeps shrinking, leading to a pattern of regionalization. The driving forces of economic globalization have gradually shifted from cost-saving to innovation. Accordingly, the benefits of economic globalization will be reallocated between developed and developing countries. The trade-offs between efficiency and resilience alter the global value chain, shifting outsourcing from off-shoring to re-shoring or near-shoring. The changing economic globalization has witnessed the rising effects of geographical distances, institutions, and resilience on increasing the inequality of the global economic geography. In economic geography, the scalar structures shifted from the global-local to the global-national-local. The relational networks evolved toward a multi-level, multi-agent, and multi-scale one. The role of the nation has been revisited. More attention has been paid to geopolitical hotspots. Overall, economic geography's institutional, cultural, relational, and evolutionary turns exhibit an emerging trend to convergence. In such a setting, domestic economic geography should find a new balance between global trends and national strategies. This study proposed seven research issues, including: (1) the practice of the Belt and Road and the pattern of inclusive globalization; (2) the economic geography of dual circulation; (3) the paths and resilience of regional development in response to the global production network restructuring; (4) the evolution and competitiveness of industrial clusters; (5) the building of multi-level innovation systems; (6) the regional sustainable development within the global environmental governance system; and (7) the impact of geo-economics on national economic security and interests.

Infrastructure construction reflects the interaction between "human" and "land" in the process of transforming and utilizing the natural environment, whose implementation process involves complex interactions between human and land. With the continuous advancement of China's Belt and Road Initiative, the significantly increased cross-border infrastructure activities on different scales, such as the global, regional, national, and urban, as well as the complex interactions between human and land involved in their implementations, have triggered collisions and conflicts between Chinese and foreign scholars on the geography of infrastructure construction. This paper systematically compares the concerns and research contexts of Chinese and foreign geographic research on infrastructure-related issues, and on this basis, it reflects the key issues of infrastructure research based on the perspective of geography. It believes that infrastructure construction reflects the various purposes and methods of how nature is transformed and utilized by human beings. At present, domestic geographical studies have focused on the economic function of infrastructure construction, while international geographical studies have paid more attention to the heterogeneity of the "human" and "land" involved in infrastructure's concern on human-land relationship. This paper insists that this academic boundary is caused by different demands of the various social development stages on infrastructure, and it is essentially a continuous process. On the basis of comparing the differences in infrastructure studies between domestic and international geography, this paper discusses how the infrastructure corrects and regulates human-land relationships from a more dynamic, multidimensional, systematic, and relational ontology perspective, and then explores the core geographical issues involved in infrastructure under the background of this new and systematic infrastructure ontology. From a theoretical perspective, this paper integrates the ontological differences in infrastructure studies within and outside China and constructs a unified conceptual framework and ontological foundation for effective dialogue between domestic and international geographical studies. From the practical perspective, under the background of "Infrastructure Going First" in China's "Going Globally" strategy, this paper also has important reference value for China's overseas infrastructure construction.

On the basis of analyzing urban SDGs monitoring and evaluation, this paper expounds the conceptual connotation of geospatial enabled monitoring and its differences from traditional statistical-based monitoring for urban SDGs. Meanwhile, through document comparison and analysis, the development and latest progress of urban SDGs monitoring and evaluation has been revealed, suggesting a transformation of urban SDGs monitoring and evaluation from traditional statistical-based monitoring to geospatial enabled monitoring. In addition, this paper systematically analyzes the research progress and current situation of geospatial enabled monitoring from the aspects of monitoring index system, geospatial data acquisition for monitoring, and monitoring ideas and methods. Results showed that the number of urban SDGs indicators is too large and the relationship is complex, with the lack of clear core and key indicators, which need to be optimized and improved according to the specific situation. The lack of standard, public and directly available data requires the development of appropriate methods for spatial data generation and multi-source data utilization, and the establishment of data products for urban SDGs monitoring and evaluation. Besides, the lack of scientific and efficient monitoring and evaluation methods is also one of the main problems facing the current urban SDGs studies. Finally, through the analysis of current challenges in urban SDGs monitoring, future research in geospatial enabled monitoring for urban SDGs are proposed, including the establishment of scientific and efficient monitoring and evaluation methods, the establishment of a standardized and unified monitoring index system, the construction of data production sharing and monitoring and evaluation knowledge service platform, and the strengthening of the application research of big earth data and related disciplines support for the monitoring and evaluation of urban SDGs.

This study focuses on the Lower Yellow River (LYR), which has experienced continuous erosion since the operation of Xiaolangdi Reservoir in 1999, and its complex spatio-temporal variation process. Using the single-step mode of the Delayed Response Model (DRM), we derive a calculation formula for the accumulated erosion and deposition volume in the LYR. The coefficient of determination R² between the simulated and observed values from 2000 to 2020 is 0.99. Currently, the LYR is undergoing continuous erosion, but the erosion rate is gradually slowing down, and the difference between the equilibrium value and the calculated value of accumulated erosion and deposition volume gradually decreases, which means that the riverbed erosion is approaching equilibrium. Additionally, we derive a formula for the spatial distribution of main channel accumulated erosion volume per unit river length in the LYR based on the non-equilibrium suspended sediment transport equation. The coefficient of determination between the fitted value and observed value from 2003 to 2015 is about 0.98-0.99, with a relative error of approximately 6.2%. Our findings suggest that under the current conditions of decreasing sediment inflow and continuous scouring, it takes around 3.0 years for the riverbed to achieve half of the erosion and deposition adjustment and approximately 13.0 years to achieve 95% of the adjustment. Moreover, the spatial distribution of accumulated erosion volume in the LYR tends to become more uniform with the continuous development of erosion. These results provide valuable reference for analyzing the complex spatio-temporal variation process of the LYR.

At present, the empirical analysis of regional dual-nuclei structures at the national level is still relatively rare. How to define the provinces with the characteristics of dual-nuclei structures and analyze their impact needs further empirical discussion. In this paper, the spatial Dubin model and the data of 259 prefecture-level cities are used to analyze the distribution characteristics of regional dual-nuclei structure in China and its influence on provincial development. The empirical results show that 11 provincial-level regions (hereafter provinces) in China show the characteristics of dual-nuclei structure. The regional dual-nuclei structure plays a significant role in promoting the economic development of the province, but the northern and southern regions show great differences. The regional dual-nuclei structure has a promoting effect on provincial industrial agglomeration and helps to promote the improvement of local scientific and technological innovation. In general, compared with some single-core provinces with small scale and weak radiation driving force in some provincial capitals, the regional dual-nuclei structure can make up for these shortcomings to a certain extent by virtue of the number of central cities and spatial distribution, which is more conducive to driving local economic development and scientific and technological innovation.

Resilience study has long been a focal point in various fields of geography, social science, urban studies, and psychology. Recently, resilience study from multiple disciplines has scrutinized at individual scale. As an important behavior in daily life of human beings, travel behavior is of spatial dependence, spatio-temporal dynamics, and individual heterogeneity. Moreover, how to understand interaction between travel behavior (demand) and traffic supply and their dynamics is a fundamental question in transport studies when transport systems encounter unexpected disturbance. Based on fundamental theories from multiple disciplines including ecology, traffic engineering, and psychology, this paper refines the definition of travel behavior resilience. Also, this paper proposes a conceptual theoretical framework of travel behavior resilience based on dynamic equilibrium characteristics of traffic supply and demand. In general, travel behavior presents three stages of variations, namely, dramatic reduction, rapid growth, and fluctuation recovery, which has been helpful to capture travel behavior resilience triangle. Then we construct a corresponding evaluation methodology, which is suitable for multi-scale and multi-dimensional perspectives. We emphasize that the evaluation of travel behavior resilience should be process-oriented with temporal continuity or capture inflection points of travel behavior. Using multi-source big data such as mobile phone signaling data and smart card data, this paper offers empirical studies on travel behavior resilience, and explores its spatial heterogeneity and group differences. With the location-based analysis, we confirm that people show the greater travel behavior resilience at places where people are engaged in various socio-economic activities. With the group-based analysis, we find that age, socio-economic attributes of mobility groups significantly affect travel behavior resilience. Overall, travel behavior resilience can be one pillar and also offer geographic perspectives to broaden resilience studies. In future, the study of travel behavior resilience on multiple scales and perspectives can explore spatial heterogeneity of traffic re-equilibrium, transport modal differences, and then contribute to urban spatial structure studies. Indeed, the study of travel behavior resilience can provide scientific and technological support for urban management and resilient city construction.

The land conversion processes concerning non-agricultural and non-grain production areas have prominently decreased arable land availability, which substantially impacted grain production capacity and threatened national food security. Thus, it is critical to establish a novel scientific approach to identify spatio-temporal evolution patterns of land conversion and its influencing factors in different stages. This study evaluates the evolutionary characteristics of non-agricultural and non-grain fields by constructing a comprehensive index system that considers factors like cultivated land resources, social and economic conditions, and farmers' subjective perspectives, using a county as the basic research unit. For a comprehensive analysis, a geographical detector model was utilized to quantify driving factors in different stages. The results indicated spatial clustering effects for non-agricultural and non-grain fields throughout China, particularly in the eastern region beyond the "Hu Huanyong Line". Further analysis revealed a spatial pattern for non-grain conversion phenomenon was more intense in the southwestern than the northeastern fields. Over the past four decades, non-agricultural fields recorded an area expansion, but the year-wise area increase was gradually reduced, while non-grain areas exhibited a "growth-stable" change pattern. Although progress in non-grain was less in primary producing areas over the last 40 years, an increase of 1.49 times and 1.33 times was recorded from 2010 to 2020 in PSB (production and sales balance area) and Mrt (marketing) areas, respectively. Compared to the period 1980-2000, the rate of non-agricultural conversion in primary producing areas decreased by 77% during 2010-2020, while the rate of non-agricultural conversion increased by 1.63 and 4.65 times for PSB and Mrt regions, respectively. Based on these findings, this paper puts forward suggestions, such as setting control rules and subsidy mechanisms according to area classification, promoting control policies based on regional considerations, strengthening dynamic monitoring and risk warning, as well as enhancing supervision and assessment.

Wetland is an important natural resource for human beings and plays an irreplaceable ecological function in the terrestrial ecosystem. In order to curb the continued loss of wetlands around the world, international organizations and many countries have taken a series of major protection and restoration measures. This paper reviews the wetland protection and restoration measures of international organizations and some countries, comprehensively interprets China's wetland protection and restoration management experience, and proposes that future research on wetland resources should be carried out from the aspects of international frontier and national strategy, social economy and intelligent services. The results show that: (1) The 27 International Wetlands Day from 1997 to 2023 provide new goals and tasks for the protection and management of wetlands in corresponding years. The important topics and outcomes of the 14 International Convention on Wetlands Conferences from 1980 to 2022 provide new directions and new challenges for wetland development in the coming period. In the future, we should enhance ecological functions of wetlands, promote the sustainable development of wetlands, and overcome the technical bottleneck of ecological restoration of fragile wetland ecosystems from 2020 to 2035. (2) During the 30-year period from 1992 to 2022, China embarked on a new phase of wetland protection and restoration. The overall experience of wetland protection and restoration with Chinese characteristics has been formed through "national strategic deployment-legal policy establishment-project planning and implementation". Emphasis was placed on the need to provide for and prepare planning for the long-term protection of wetlands at the national legal level, to innovate restoration and management techniques and application systems, and to effectively address the complex issues of wetland protection and restoration through collaborative division of labor among multiple departments. (3) The research on the future trend of wetlands should be directed towards the exploration and practice of "United Nations Sustainable Development Goals and several international conventions" in support of the sustainable development of wetlands. Wetland protection, restoration and management services should be promoted for "national strategic needs and local social and economic high-quality development". Research on the cross-integration and academic innovation development also should be enhanced for "disciplinary development - global supervision - comprehensive assessment-intelligent decision-making".

Deconstructing rural spatial characteristics is the precondition for building rural spatial governance system in the new era, and multi-scale rural spatial characteristics and its governance path would effectively support the modernization of the national governance system. Based on the comprehensive, regional and mobile thinking paradigm of geography, this paper deconstructs the multi-scale rural spatial characteristics, identifies its internal operating logics, summarizes its governance dilemmas, constructs a multi-scale rural spatial governance framework that is based on geographical analysis paradigm, explores feasible governance paths, and constructs a multi-scale rural spatial governance system research plan, namely, "characteristics identification-dilemma analysis-governance framework-governance path". The paper finds that: (1) to analyze the operating logics of the multi-scale rural space through the comprehensive, regional and mobile analytical thinking of geography, it is necessary to understand the mechanism of action of scale synthesis, scale differentiation and scale flow to the multi-scale rural spatial characteristics, highlighting the comprehensive characteristics of rural space, strengthening rural spatial heterogeneity, and integrating rural spatial mobility. (2) The lacking urban-rural spatial overall planning, unsmooth spatial mobile network and not-reflected different types of rural spatial value are the key dilemmas in the rural spatial governance, which need to be addressed. (3) The multi-scale rural spatial governance framework of "comprehensive spatial governance-spatial zoning governance-spatial mobile governance" could effectively solve the problems of urban-rural spatial integration, regional spatial coordination and spatial network blockage. (4) Integrating urban-rural comprehensive governance, innovating regulation control to improve regional governance and balancing the configuration of spatial development right to achieve mobile spatial governance are feasible paths for multi-scale rural space governance. In conclusion, clarifying the multi-scale rural spatial characteristics in the new era and constructing a scientific governance system could provide theoretical support to promote integrated urban-rural development and rural vitalization strategy.

The study of the new economic geography has paid attention to the polarization and balanced development of urban systems. In reality, however, transport accessibility is subject to great uncertainty in explaining the polarization and balance of the urban system. In fact, the polarization or equilibrium of the regional urban system is not only unique in China, but also a general phenomenon in countries with different development outcomes, political systems and degrees of marketization. From the perspective of industrial heterogeneity, this study empirically analyzes the process and mechanism of the industrial structure of regional central cities on the population growth of neighboring cities in China from 1980 to 2020, and examines the influence of industrial structure on the polarization and equilibrium development of the regional urban system. The results show that, firstly, the manufacturing sector strengthens the spillover effect from the core city and promotes the population growth in neighboring cities, while the service sector weakens the spillover effect and hinders the growth in neighboring cities. Secondly, the manufacturing-oriented cities have relatively small city scale, while the service-oriented cities are relatively large. Therefore, the driving effect of manufacturing-oriented central cities on the neighboring cities is larger, which tends to produce a relatively balanced regional city system. Correspondently, the spillover effect of service-oriented central cities on the neighboring cities is smaller, which tends to form a relatively polarized regional city system. Finally, as the share of services in the industrial structure of central cities continues to rise, China's urban system may become more polarized rather than balanced. Certainly, the higher the proportion of manufacturing in the central city, the more balanced the regional urban system is. In fact, the empirical results show that the industrial structure and the spillover effect of the core city have an inverted U-shaped relationship, i.e. a high proportion of manufacturing or services weakens the driving effect of the core city on surrounding cities. The reasons for this vary. The high proportion of manufacturing and the small size of the central city have a limited spillover effect on the neighboring cities and therefore can hardly drive their growth; while the high proportion of service industry and the negative effect of the service industry on the spillover effect lead to the slow development of the neighboring small-and-medium-sized cities. It is worth noting that because of the significant spatial impact of industry on the urban system, the future regional urbanization strategy should be coordinated with the industrial strategy. More importantly, with the gradual liberalization of the household registration system, industry selection can become an effective policy option for macro-control of the regional urban system.

According to the Ministry of Water Resources of the People's Republic of China, the number of casualties in flash flood disasters accounts for nearly 70% of flood disaster casualties in recent years and flash flood has become one of the major natural disasters causing casualties in China. Flash flood regionalization is fundamental for implementing the local measures of the flash flood prevention and mitigation according to local conditions. Using results from existing flash flood relevant physiographical regionalization schemes, and in accordance with the principles of comprehensive, dominant factors, the relative consistency within units, the relative difference between units, the integrity of spatial distribution and the hierarchical divisions, this paper firstly constructs an index system of the flash flood trigger factors and its underlying surface environment for the flash flood regionalization in China. In the combination of top-down and bottom-up regionalization, the hybrid self-organizing-map-based spatial clustering algorithm is then built. Finally, nine homogeneous regions at the first-grade and thirty-three subregions at the second-grade are delineated for flash floods in China. The historical flash flood events and the Geodetector method are adopted to evaluate the developed regionalization schemes. Results show that the first-grade and the second-grade flash flood regionalization schemes in China can respectively provide the determinant power of 66.4% and 75.4% for the spatial distribution of historical flash flood events in the whole country, indicating the developed flash flood regionalization has a good spatial consistency with the distribution of historical flash flood events with different densities. The developed flash flood regionalization not only effectively delineates the regional differentiation pattern of flash floods, but also provides a scientific basis for the implementation of localized flash flood prevention and mitigation measures in China, which benefits for the sound development of flash flood disasters prevention and management in China.

As the third pole of earth, the Qinghai-Tibet Plateau is an important ecological security barrier in China and an ecologically sensitive area of global climate change. The increasing climate change has posed a major challenge to its ecosystem function and stability. This paper first analyzes the spatiotemporal variation characteristics of the ecosystem pattern of the Qinghai-Tibet Plateau and its key functions including water conservation, soil conservation, windbreak and sand fixation from 2000 to 2020, clarifies the regional differences in ecosystem functions and their importance, and further evaluates the stability of ecosystem functions. And there is no doubt that the stable state will lay a scientific foundation for the plateau to build an ecologically civilized highland and launch protection and restoration projects. The results show that: (1) From 2000 to 2020, the wetland area of the study area increased and the grassland area decreased significantly. The water conservation and windbreak and sand fixation capacity were improved, and the annual change rates were 3.57 m³/(hm²·a) and 0.23 t/(hm²·a), respectively. However, the overall soil conservation showed a downward trend with an annual change rate of -0.16 t/(hm²·a). (2) The core areas of water conservation, soil conservation and windbreak and sand fixation accounted for 12.7%, 13.9% and 14.2%, respectively. The core water conservation barrier areas were mainly located in southeast Tibet, Sanjiangyuan and Ruoergai. The core windbreak and sand fixation areas were concentrated in the central and western parts of the plateau, and the core soil conservation areas surrounded the plateau. (3) From 2000 to 2020, the water conservation, soil conservation, and wind protection and sand-fixation functions have shown relatively high stability in the southeastern and central parts of the plateau, while relatively weak stability in the western part of the plateau. Combining stability assessment and ecological protection and restoration practices, we can divide the Qinghai-Tibet Plateau into three major categories of 16 ecosystem function zones and carry out differentiated ecological protection and restoration for different core ecosystem functions and zones.

As China's urbanization has entered the middle and later stage and the improvement of well-being of residents has become a core goal, the transformation from "top-down" system goals optimization on the supply side to "bottom-up" multi-dimensional goals coordination on the demand side has become a new perspective to understand the connotation of urbanization. Based on the perspective of the human living conditions, the humanities environment, and human-city relationship, this paper constructs a connotation framework and index system of urbanization. Furthermore, Theil index is employed to analyze the spatio-temporal differentiation characteristics of China's urbanization before and after the implementation of the new-type urbanization strategy. Finally, in terms of both direct and indirect effect mechanisms, the mechanism framework of urbanization differentiation is constructed, and its evolution pattern is revealed by using Variance Decomposition and Geodetector. The results show that: since the implementation of the new-type urbanization strategy in 2014, China's urbanization has made remarkable achievements, with a steady improvement in human living conditions and human-city relationship, and there is still much room for improvement in the humanities environment. The high-level areas of urbanization are mainly distributed in coastal areas, and expanding to inland areas along the Yangtze River Basin and Yellow River Basin. The regional differences of urbanization gradually decrease, but the contribution rate of inner-regional differences shows an expanding trend. Differences in human living conditions and human-city relationship are the main factors of urbanization differentiation, but the contribution of differences in humanities environment is gradually expanding after 2014. Opening up and scientific & technological innovation are the main influencing factors of the difference in human living conditions. With the implementation of the new-type urbanization strategy, the impact on differences in humanities environment of the government finance gradually diminishes. Resource endowments have a relatively strong influence on differences in human-city relationship. This study can provide theoretical and empirical support for promoting the development of urbanization in China.

The shipping service industry is a major driving force in the economic growth and reorganization of port cities' spatial structure, as well as a core element in raising hub port cities' competitiveness. Recently, the global distribution and network connections of the shipping service industry have attracted significant attention, but few studies have analyzed the distribution differences and influencing factors of different shipping service industries. In this study, we divided the shipping service industry into upstream shipping auxiliary industries (ship owners, ship management, ship repair and construction) and downstream shipping derivative service industries (shipping finance, shipping insurance, maritime law). And based on Lloyd's Maritime Directory in 2019, we built a database about the world's shipping service industry. The spatial connection network of the global shipping service industry was then examined at the global, regional and city levels, using the correlation network model and the negative binomial regression model, which revealed the differences in distribution between the upstream and downstream shipping services. The affecting elements on upstream and downstream shipping services are explored in the last section. The results are as follows: (1) Europe and Asia are the primary distribution region of the upstream and downstream shipping service industries, a pyramid structure is shown under the variation in countries' distribution. The spatial distribution of the upstream industry is wider in range, closer in connections and stronger in agglomeration, compared to the downstream industry. (2) The global shipping service network presents a dual-center structure. Europe centers on London and builds a trans-continental radiation network of downstream shipping derivative services connecting to neighboring capital cities. Asia forms an upstream service network that connects Hong Kong, Shanghai and other cities with Singapore as the center. (3) The upstream shipping auxiliary industry is mainly distributed in non-capital seaport cities, while the downstream shipping derivative service industry is chiefly distributed in the capitals and other administrative centers. (4) The e-commerce index and the logistics performance index are positively related to the upstream and downstream industries. Otherwise, the upstream shipping auxiliary industry is also affected by the degree of economic freedom, the number of tourist arrivals, and the liner transport index, while the downstream shipping derivative service industry is mainly influenced by international trade and political culture. This study provides a theoretical reference for China to construct an international shipping center, reaches the linkage development between upstream and downstream shipping services, and improves the overall strength of China's shipping industry.