The long-term supply-demand imbalance of rural land use functions (RLUFs) is one of the main reasons for rural issues in China. Based on the multifunctionality theory, this study explained the mutual relationship between rural land consolidation (RLC) and rural vitalization with a focus on supply-demand and element-structure-function relationships, and then discussed how to realize the supply-demand balance of RLUFs through RLC so as to promote sustainable rural development. The results show that: 1) Comprehensive rural land consolidation is a multifunctional land use method and an important means to solve rural issues for promoting rural vitalization. In essence, it is the transition from productivism that focuses on economic benefits to non-productivism that takes social, economic, and environmental benefits as a whole. 2) RLUFs include production, living, ecological, and cultural functions, corresponding to the economic, social, enviromental, and cultural demands of rural vitalization. The production functions are divided into agricultural, commercial, and industrial functions, and living functions include residential, employment, and public service functions. 3) Along the path of integrating land use elements, restructuring land use structures, and optimizing land use functions, RLC promotes the supply-demand balance of RLUFs from the supply side according to local conditions. 4) In future research, the mechanisms and modes of RLC impact on rural vitalization at different spatial scales, as well as quantitative analysis of the functional supply of land use and the functional demand of rural vitalization under the influence of RLC should be given more attention, thus laying a scientific foundation for the formulation and implementation of land use and rural vitalization planning.
Sustainability transitions focus on the fundamental transformation of the existing socio-technical system towards a more sustainable mode of production and consumption. Emerged in Europe two decades ago, this new research field has already exerted impacts on the green transition policy practices of many countries and regions. In recent years, transition studies have increasingly taken geography into account, resulting in a new paradigm of geography of sustainability transitions. This emerging paradigm focuses on the role of spatial embeddedness and multi-scalar interactions in explaining where transitions take place. This article provides a critical overview of the development in the geography of sustainability transitions research, and suggests five promising avenues for future transition research in the Chinese context: 1) to develop concepts and theorize from the Chinese context; 2) to link sustainability transitions with latecomer regions' industry catch-up; 3) to compare the sustainability transitions in cities with different leading industries; 4) to pay more attention to the role of local agency through the lens of multi-scalar interactions; and 5) to explore the impact of digitalization and artificial intelligence on sustainability transitions.
The purpose of adaptation research is to reduce the negative effects of external environment and improve adaptation through the adjustment of the subject to the changes of the external environment, which is an important way to realize the sustainable development of human-environment systems. In view of the lack of a unified understanding and systematic review of the adaptation theories, this article summarized the progress of research on adaptation from the concepts, theoretical frameworks, and methods by examining the literature on adaptation of human-environment systems in China and internationally, and put forward a scientific paradigm of adaptation research. The findings are as follows: 1) There is no scientific consensus on the concept of adaptation in academia, which hinders the construction of a general theoretical system of adaptation research. 2) The existing analytical frameworks of adaptation are mostly based on the extension and revision of the theoretical framework in the field of global change. 3) There is no representative method in adaptation research, which mainly uses vulnerability and resilience assessment methods and index systems. Therefore, the construction of a unified concept and theoretical system of adaptation needs to be strengthened. The existing theoretical research in other countries may not be universally applicable, and an analytical framework and method of adaptation research specifically useful in China should be an important research direction in the future. Simultaneously, it is necessary to strengthen the research on integrated adaptation of human-environment systems considering both human society and the natural environment, and pay attention to the dynamic analysis of adaptation with a combination of multiple scales.
The relationship between urban and rural areas in China has been an important relationship for economic and social development and a major concern of the party and the government. In order to explore the relationship between urban and rural areas and its governance logic, the CiteSpace software was used to analyze the research hotspots of rural-urban relationship since the reform and opening up in the 1970s and to interpret its change based on the historical background, and then reveal the contextual characteristics of rural-urban relationship and the internal logic of governance reform. The research shows that since the reform and opening up, rural-urban relationship has gone through four stages—from an improving urban-rural relationship, to rural-urban re-separation, rural-urban relationship adjustment, and integrated rural-urban development. The process reflects the governance logic of breaking the rural-urban division, favoring the urban field, balancing rural-urban development, and promoting rural-urban integration. Since the 19th National Congress of the Communist Party of China, the relationship between urban and rural areas has developed in the direction of rural-urban integration. Rural-urban co-governance is the internal demand and governance trend of integrated rural-urban development in the new era. Finally, the article discussed the prospect of integrated rural-urban development and rural-urban co-governance from the aspects of abolishing the rural-urban dual system and establishing new supporting systems and mechanisms, breaking disciplinary boundaries and integrating interdisciplinary knowledge and cross-application of practice, and organically combining the two strategies of new urbanization and rural revitalization.
Since the beginning of the 21st century, the conflict between the degradation of ecosystem services (ES) and the increase of human needs has become increasingly intensified. How to improve the interrelationship between ecosystem services and human well-being (HWB) towards a coordinated and balanced state naturally becomes a core theme of sustainable development. Based on the reviews of ES-HWB interrelationship through three phrases, the existing research mainly started from the influences of ES on and responses to HWB, and further focused on the practices of their interrelationship through some key fields including supply-demand relationship and spatial flows, trade-offs/synergies, valuation of cultural ecosystem services, payments for ecosystem services, and optimized regulation and sustainable management. However, the interrelationship research is still led by "influence chain" of the ES cascade while distinct deficiencies exist in terms of theoretical framing, technical methods of direct interrelationship measurement, and support applied for sustainable management. Moreover, the ES-HWB interrelationship tends to become more nonlinear, which urges for certain theoretical innovation from synthetic integration paradigm of the coupled human and natural system framework. This article, therefore, proposed a new path for the ES-HWB interrelationship research—from cascade to coupling, with which the interactive coercing effect and its intrinsic dynamic change mechanism are clear to distinguish in a systematic way. On this basis, an exploratory theoretical research framework of ES-HWB coupling was built with a main thread of "interactive coercing effect measurement-coupling relationship deconstruction-coupled pattern and process evolution-coordinated management and application", so were the technical coupling approaches. In such regards, the ES-HWB coupling research is bound to develop as a pivotal issue enriching the coupled human and natural system studies. First, there is a need to untangle ES-HWB interrelationship as a foundation. Then, further in-depth research should be enriched to achieve the orderly and coordinated development oriented by ecological civilization, including the decoupling of coupled interactions, transmission mechanism and dynamic integration, human needs-oriented differentiated evolution, and sustainable optimization based on the ES-HWB coordination.
The spatial heterogeneity of urban built environments is a primary challenge in the research of urban pluvial floods in terms of the model representativeness, computational efficiency, and data requirements. The development of new technologies, including artificial intelligence, big data, and remote sensing, provides opportunities for the research of urban pluvial floods, such as efficient approaches and high-resolution data. This study conducted a comprehensive review of the research progress on urban pluvial floods from four perspectives—flood characteristics, mechanisms, data, and research methods, and finally came to four conclusions: 1) Urban pluvial floods have typical features such as short duration, scattered and evolving spatial distribution, chain effect, and sharp increase of losses at the critical scenario. 2) Micro-topography plays an important role in the spatial distribution of urban pluvial floods, and the topographic control index shows the potential of identifying frequently flooded areas. 3) The highly variable rainfall processes are the bottleneck in the near-real-time flood simulation, and the radar rainfall data provide a solution. Internet-based big data provide a new way to extract flood inundation data with high spatial coverage, but still face the problems of quality control and fusion with multi-sources data. 4) Machine learning could be coupled with hydrodynamic models to improve the efficiency of near-real-time flood simulation.
In the new era, oil and gas are still the core contents of energy power games, the attributes of energy power are very different, and the connotation of energy security and energy strategy has also changed. Based on a systematic review of energy geopolitics, this study put forward the concept of energy power, and found that the global energy situation is undergoing profound changes. Instead of taking the "oil power" generated by the possession and production rights of fossil energy as the only core, global energy research has expanded to multi-dimensional energy power, and the power connection has expanded from competition and cooperation to the complex energy network relationship. The research elaborated specifically from four aspects: geopolitical pattern, energy security concept, energy network, and global energy governance: 1) The core of traditional energy geopolitical research is energy distribution, spatial change of production and marketing, and their patterns, and the imbalance of oil and gas resources geographic distribution is the most direct factor of energy power generation. 2) From the oil crisis era with supply security as the core, to the collective action formed around energy interdependence, and the new order of global energy governance in the new energy era in the future, the different views of energy security are the important factor leading to the change of international energy geopolitical power. 3) Energy as commodity and the geographical attributes of energy determine that energy trade is not only an economic behavior, but also closely related to international politics. The separation of production and consumption makes trade control and channel control in the secondary distribution of oil and gas an important influencing factor on the reconstruction of energy power. 4) The change of global energy power and complex energy power network will lead to a new order of global energy governance system. The main holders of power have changed from countries, international organizations, and multinational companies to communities of interest in the global energy network. The theme of energy governance has changed from the interests of countries to the redistribution process of global energy power. In future studies, academic research of energy geopolitics should focus on the following issues: how to construct a new theory of multi-dimensional energy power system; how to evaluate the influence of new factors such as climate change and renewable and sustainable energy development; how to understand the inter-relationship between energy power and geographic space under globalization; how to reconstruct the order of global energy power and simulate its effect, and how to clarify the new energy governance mechanism and governance patterns. These themes are important energy geopolitics research propositions, and are of great significant for understanding and predicting the future energy situation and change in energy strategies.
In the context of global climate change, extreme weather events and the concomitant natural disasters are becoming a primary risk restricting the socioeconomic development in coastal areas that are often highly urbanized. This study sets out to explore the new characteristics of natural hazards and disasters in the coastal areas of China against the backdrop of a changing climate. Major conclusions are as follows. First, the occurrences of extreme weather and climatic events are considerably uncertain. The climate and disasters are different across various temporal and spatial scales, and the components of the disaster risk system become more complicated. Second, in view of the new challenges brought by climate change, we suggest paying close attention to three issues in the future, including the change of temporal and spatial scales that are used to depict the disasters, the synergism of multi-disasters, and the effects of climate change and urbanization. Based on these, a new framework of disaster risk system is established to reflect the qualities of disasters in complex spatiotemporal contexts. Lastly, to develop more effective coping strategies for the climate and natural hazards and disasters in coastal areas, it is necessary to promote diversification of the disaster prevention system and enhance its robustness, and to strengthen the self-recovery capability of the social, economic, and ecological environments. Meanwhile, information sharing in multi-disaster management and risk sharing and transfer policies are also important for accommodating the negative impacts of extreme events and disasters coming with climate change.
Tree-ring density is one of the important proxies for climate reconstruction. In the past few decades, international and Chinese scholars have carried out a large number of studies on the relationship between tree-ring density and climate, and many climate series were reconstructed for different regions. In this study, we collected publications about the responses to climate change and climate reconstruction based on tree ring density, and reviewed some progresses in these areas. Although the relationship between tree-ring density and the climate may be affected by tree species, terrain (altitude, slope direction, and so on), and other factors, the maximum latewood density is a well-known proxy of summer or early fall temperature variation in cold and moist areas, while earlywood density can be used to reconstruct precipitation variation in arid areas. Therefore, most of the scholars reconstructed the temperature of the summer or the late fall, and only few precipitation and sea level pressure series were reconstructed based on tree-ring density. In addition, the variance that the reconstruction can explain varies from region to region, and from tree species to species. To date, the reconstruction series spanned 2018 years in Europe, which is the longest in the world, and 449 years in Southwest China, which is the longest series in China. There still exist controversies around the divergence in tree-ring density response to temperature and the cooling effect of volcanic eruptions, because of the unstable relationship between tree-ring density and temperature. Future research should pay more attention to the relationship between tree-ring density and other climate variables such as precipitation and light, and the influence of nonclimatic factors such as altitude, tree species, and experimental methods.
A key challenge of social-ecological system governance is to effectively accumulate and transfer successful strategies across heterogeneous contexts. The context-dependence of social-ecological dynamics makes it extremely difficult to draw general conclusions about the determinants of effective governance. Generic design factors can be too abstract to be applied to concrete problems because every case is different. Archetype analysis is a particularly salient approach in this regard that helps researchers to understand and compare patterns of (un)sustainability in heterogeneous cases. This article clarifies the concept and characteristics of archetype, expounds on the significance of archetype analysis, and reviews the progress of archetype analysis in the key research fields of social-ecological system governance. The result reveals that: 1) Archetype analysis generally investigates recurrent patterns of the phenomenon of interest at an intermediate level of abstraction to identify multiple models that explain the phenomenon under specific conditions. 2) Archetype analysis is best conceived as a methodological approach, rather than a particular method, framework, or theory. 3) Archetype analysis can promote the accumulation and transfer of case study knowledge, is compatibility with multiple research methods, and can achieve a certain degree of predictability in social-ecological system governance. 4) Archetype analysis is based on "type-subtype" multi-level analysis, which helps to find the "strong" causality of the complex social-ecological system. 5) Archetype is not only the result of the research but also the starting point of the research. The test, modification, improvement, and validation of the archetype are also an important direction of future research.
With the further development of new urbanization and implementation of the rural revitalization strategy, spatial governance in metropolitan fringe is worthy of attention. As the metropolitan fringe is located at the junction of urban and rural areas, population, society, resources, and other issues in metropolitan fringe reflect the urban-rural conflicts. Therefore, the spatial governance in metropolitan fringe is of great significance for the balanced development of urban and rural areas. As collaborative governance of multi-subjects is a clear requirement for the improvement of national governance system and governance capacity, it is important to examine how to realize the spatial governance of multi-subjects coordination in metropolitan fringe. Based on the perspective of multi-subjects, this study examined the theoretical framework, structure, issues, mechanisms, and paths of spatial governance in metropolitan fringe, and drew the following conclusions. First, through the literature and theoretical analysis of the relationship between the governance subjects and the spatial characteristics of metropolitan fringe, this article summarized the theoretical framework of spatial governance in metropolitan fringe from the perspective of multiple subjects. It showed that with the transformation of governance subject in metropolitan fringe from single subject to multi-subjects coordination, urban and rural spaces gradually develop to a balanced state. Second, by exploring the historical development of metropolitan fringe, this study concluded that the spatial governance structure of metropolitan fringe has gradually transformed from single center structure to multi-centric network structure. Third, in the process of spatial development in metropolitan fringe, the multi-subjects follow the principle of maximizing their own interests to compete for resources. The competition for spatial resources causes three problems of spatial governance, which are the diversification of material space, the differentiation of social space, and the imbalance of spatial power. Fourth, the multiple subjects follow their own spatial governance needs and logic to implement the corresponding governance mechanism for the urban fringe. Finally, based on the cooperation of multi-subjects, the optimized path of spatial governance in metropolitan fringe is concluded. Based on the above conclusions, this article summarized and constructed the progressive research framework of "governance structure-governance issues-governance mechanism-path optimization". At present, the research of spatial governance still needs to be improved. In order to promote the institutional turn of human geography and constantly expand the research field, it is vital to strengthen the research on the spatial relationship, governance mechanism, and path optimization of multi-subjects and metropolitan fringe.
There exist two types of epistemology of materialism in current fields of geographies of consumption. One follows the principles of re-materialization on the foundation of dualistic dialectical materialism raised by Marx. Another school relies on the ontology of monism, relationality, and process, which also makes a profound impact on the understanding of geographies of consumption. The latter is classified into the school of thought of new materialism, which provides a more subtle and comprehensive understanding of the nonlinear relationships among places, subjectivities, the environment, material, representation, and so on, endeavoring to break up the long-standing dualism in former research in consumption geography. Thus, this study reviewed and summarized the research progress of consumption geography studies from the perspective of new materialism in order to bring a new ontology and epistemology. Drawing from the actor network theory (ANT), assemblage theory, more than human theory, and nonrepresentational theory, studies followed new materialism highlight material agency, dynamics, and impact on consumption networks. Furthermore, this article indicates the shifting connotation of geographies of consumption: Material in consumption not only acts as the entry point of investigating social relations among people but also actively engages in the process of consuming practices or even reshapes the consumption space; Subjectivities of consumers are produced in events, processes, and relations instead of only produced by social construction or discourse; Socialities are transformed from the linear relationship between consumers and producers to topological relations among consumers, producers, and other nonhuman subjects. On the basis of these shifting contents, this article concludes three different categories of the research process: embodied consumption practice and consumers' subjectivity; consumption space and affect; lively commodities and human-nonhuman-place relationship. At the end of this article, some reflections and outlooks are brought to fill in the gaps of current geographies of consumption in China. New materialism provides a new entry point in understanding subjectivities and socialities in geographies of consumption, especially insightful in solving transformation of consumption pattern and sustainable consumption; lively commodities and consumers' affect; Internet, technology, and reconstruction of consumption space.
In the past 20 years, many paleohydrological investigations have been carried out in the Yellow River Basin. Based on the previous studies, this article systematically reviewed the progress of research on paleoflood events in the Yellow River Basin since the Last Deglaciation. Firstly, we reviewed the major findings on the identification of paleoflood events, the establishment of chronological framework of paleoflood events, and the climatic background of paleoflood events. Secondly, the reconstruction of peak water level and peak discharge of paleofloods and the social impact of paleoflood events were summarized. Thirdly, the main problems and recommendations in relation to accurate dating of paleoflood deposits, the causes of paleoflood events, and hydrological reconstruction of paleoflood events were proposed. Finally, we examined the prospect of future research in this field: 1) Strengthen the ability of modern flood monitoring, improve the understanding of flood-generating mechanisms, and then effectively evaluate the influence of hydrological model parameters on the result of paleoflood hydrological reconstruction. The ideal places (bedrock gorges) for paleoflood hydrological reconstruction, based on the paleoflood data, strengthen the research in the occurrence frequency and recurrence period of small probability extreme flood events, and enhance the ability of prediction and evaluation of major flood disaster events in the Yellow River Basin. 2) The whole Yellow River Basin needs to be considered for paleoflood study. We should strengthen the comprehensive analysis of paleoflood events in different time scales and reaches, especially the paleoflood events in the upper, middle, and lower reaches of the Yellow River. In addition, the paleoflood events in the Yellow River Basin should be studied synthetically from multiple perspectives, and paleoflood database needs to be established as soon as possible. This review may provide some historical basis for flood prediction, prevention, and risk assessment as well as ecological protection and high-quality development of the Yellow River Basin under the background of global change.
The implementation of ecological restoration of territorial space is an important way to construct ecological civilization in the new era. The arrangement of ecological protection and restoration is the precondition and basic link for scientifically carrying out ecological restoration, which affects the protection implementation, the effectiveness of engineering restoration, and the allocation of social resources. Based on the analyses of the relationship of the concepts related to ecological restoration, and from the perspectives of region identification and temporal sequence identification, this study used bibliographic analysis to examine the current research status of the ecological restoration arrangement internationally, and reviewed the application of the theoretical paradigm of landscape "pattern-process-service-sustainability" in the study of the arrangement of terrestrial ecological restoration. This article identified six important research trends, including the construction of ecological protection and restoration goals that support sustainable development, the balance of spatial and temporal needs for ecological restoration based on social satisfaction, opportunity cost-oriented ecological restoration cost evaluation, natural solutions based on ecological rigid constraints, decision-making threshold of ecological protection and artificial restoration under the concept of resilience, and location decisions for ecological protection and restoration projects based on spatial and temporal simulation, to construct a terrestrial ecological restoration arrangement research system coupled with social-ecological goals. It may provide a reference for the research and practice of ecological restoration of territorial space.
Urban functions are an important basis for city identity and the formulation of development strategies. Urban functions have development stage, hierarchical, and regional characteristics. It is urgent to analyze and summarize the research results of different scholars in order to grasp the pattern of urban functional characteristics and formation mechanisms. The results show that: 1) The functional characteristics of different stages of urban development include political and commercial functions in the agrarian society; and manufacturing, trade, and logistics functions in the industrial society. The post industrialization stage is characterized by the service industry, and productive services are the main functions. 2) With regard to the functional characteristics of different city scales, the higher the city level, the more comprehensive the urban functions and the stronger the service functions. 3) At different spatial scales, cities present different functional characteristics. 4) Traditional factors such as natural conditions, population, transportation, government guidance, and location play a fundamental role in the evolution of urban functions, while new factors such as science and technology, globalization, and informatization play an increasingly important role. The evolution of urban functions is also affected by regional division of labor, industrial upgrading, industrial transfer, convergence development, and other mechanisms. 5) In the future, we should include and improve the long-temporal scale and recent research on urban functions, deepen the research on urban function effect, urban function evolution mechanism, and function optimization, and promote the integration with national strategies. In addition to statistical analysis, the research methods should be supplemented by field survey, questionnaire, interview, and other methods.
In view of the plight of spatial practice in the urban transformation of China, it is urgent to use the theoretical paradigm of spatial power and the value system of spatial justice to reflect on and reconstruct China's urbanization development model and its spatial governance. Urban political geography is based on the spatial power thinking of political geography, and draws on the research of urban politics and urban sociology on "urban politics" and "urban power" to expand the political attributes of urban space. However, based on China's national conditions and urban practices, it is necessary to explain the "political" meaning, "space" expression, and value orientation of urban political geography in China from a realistic level. Finally, on a realistic level, based on the "problem-driven" approach, this article put forward five important priority issues that should be paid attention to: urban spatial coordination game theory, urban institutional arrangements for spatial justice, value-based urban living space research, research on urban production space based on power, and research on urban ecological space based on responsibility.
Energy is one of the core topics of geographic research. As a typical activity involving regional human-land relationship, household energy consumption is a major trend in the refined research of energy geography. Based on the spatial scale perspective of geography, we reviewed the origins of energy geography research, the spatial characteristics of household energy consumption, formation mechanism, and data sources. Three main conclusions are drawn: 1) Constructing a panoramic survey framework of household energy data, including the geographical type, energy type, quantity, and use in the scope of the survey. 2) Meso-scale research needs to be strengthened. Coordination through the micro-medium-macro-scale relationship is conducive to understanding and grasping the characteristics and patterns of household energy consumption from a nested structure as a whole. 3) Constructing a comprehensive analysis framework of multi-factors such as household attributes, geographic factors, and lifestyles, and analyzing the dynamic drivers for the formation of spatial characteristics of household energy consumption, to realize the essential understanding of the spatial differentiation process of household energy consumption. This study contributes to the internationalization of energy-related spatial research and practice in the field of geography, and has positive significance for supplementing the theoretical perspective of Chinese household energy consumption research.
With the increasing severity of global environmental problems, scholars found that apolitical studies could not work on the environmental crises effectively, so they tended to seek for a more profound perspective to fix the environmental problems. Thus, political ecology has gradually become a critical field of environmental research in different disciplines. The core theme of political ecology is to trace political factors influencing environmental issues. Based on this theme, geography, a key discipline on human-environment relation studies, enhances the spatial and political perspectives in political ecology studies. It uses its professional strength, such as scale, region, and landscape to study political ecology. Summarizing theories and topics about political ecology from the perspective of geography has practical and theoretical meanings for the construction of Chinese ecological civilization. This study first mapped the theoretical timeline of political ecology and pointed out that the theories of political ecology are rooted in early environmental criticism, cultural ecology, Marxism, poststructuralism, and posthumanism, in line with the history of geographical thoughts. Political ecology claims that the understanding of environmental issues needs to be placed on broader social circumstances, uncovering the spatial conflicts among various actors including human and nonhuman in the consequence of conversation from physical nature to social nature. Second, this study analyzed nearly 30 years of literature on political ecology research in geography in the Web of Science core database, drawing a conclusion that relevant studies mainly focus on four topics: 1) ecological economics and green-development, focusing on spatial accumulation and flow of green capital; 2) environmental governance and conservation, revealing discourses producing various spatial forms in conservation; 3) environmental identity and micropolitics, demonstrating the negative and positive effects on micro environmental practices; 4) the object of ecology and agency, paying attention to how nonhuman's agency disturbing and cooperating with human politics. Finally, we conclude that the ultimate goals of political ecology from the perspective of geography are to reveal the inequality of social relations behind environmental space and to seek social improvement programs. Furthermore, based on the topics of political ecology research in geography, we put forward four future directions of political ecology research in China from the perspective of geography.
Within the context of globalization and informatization society, inter-city competition is no longer bound to the scalar attributes of individual cities, such as geographic location, administrative hierarchy, population size, and so on, but rather increasingly depends on their positions in the division of labor and multi-scalar spatial functional linkages. Along with the current tendency of urban networking and clustering development, megaregion has become the spatial organization pattern with global significance in response to the present new competition and corporation situation. To understand megaregions in China, the differentiation and relationships between different concepts of urban functional regions in both Chinese and Western urban geography studies were systematically examined. The Chinese native concept of "Chengshiqun", as an urban region with flexible scale, is mostly similar to the concepts of mega-city region, megapolitan area, or megaregion in Western academic literature. To make it simple, we used the concept of megaregion to refer to the Chinese "Chengshiqun" in this article. In terms of the spatial meanings, we argue that a megaregion is: 1) a mega urbanized region consisting of more than two urban systems; 2) an urban system with both morphological continuity and functional cohesion; 3) a mega economic unit produced and shaped through the interaction of globalization and localization; and 4) a type of scale fix in today's urban and regional division and integration of labor. Specifically, the basic conditions for the development of megaregion mainly include high comprehensive carrying capacity of resources and environment, close spatial proximity of the metropolitan area to multiple single urban systems and compactness in geographic space, well-developed infrastructure networks, coordinated functional division and economic linkages, and relatively coherent social network and cultural identity. In future studies, we should pay special attention to exploring the spatial agglomeration effects and evolution of megaregions from the perspectives of relational geography and city network.
The increasing trend of extreme precipitation has become stronger globally, and is expected to have detrimental impact on agricultural ecosystems. Rice is one of the staple foods, and the inter-annual fluctuation of rice yield is highly affected by extreme precipitation. However, the mechanisms and spatiotemporal sensitivity of rice yield to extreme precipitation have not been clarified. This review summarized the temporal and spatial patterns of extreme precipitation in the main rice-producing regions of the world and its impact on rice yield, and explored the mechanism of extreme precipitation impact on rice growth and yield from the perspective of physiological, chemical, and physical processes. The input data and advantages and disadvantages in application of the main research methods, including statistical model and crop model, were evaluated and compared. The results indicate that an increase of 1% in extreme precipitation led to a decrease in rice yield by 0.02%-0.5%, mainly through increased nutrient loss and flooding. Yet, large uncertainties still exist in rice yield prediction of current studies, because it is difficult to clarify how rice yield responds to different characteristics (intensity, frequency, and duration) of extreme precipitation and its spatiotemporal sensitivity, and the mechanisms of extreme precipitation affecting rice yield components are not well understood. In addition, lacking the integration of crop models and statistical models also introduces uncertainties. We recommend to promote the integration of multi-methods, especially field observation, controlled experiment, and model improvement, to quantitatively analyze the mechanism of extreme precipitation impact on yield components, and to improve data accuracy to better simulate rice yields under extreme precipitation events in the future. Achieving these progresses will lay a foundation for optimizing the current rice cropping system and agricultural management to mitigate the impact of extreme precipitation.