Research progress of international rivers in China

China possesses over 110 international rivers and lakes, among which 41 are major ones and 15 are of great importance. With the highest concentration of international rivers, the northeast, northwest and southwest regions of China enjoy abundant transboundary resources and pose complicated ecological security issues. Following the 1950s, relevant studies on international rivers fall into three periods: 1) the planned economy period of the 1950s-1980s when border development and basic research were scant; 2) the reform and opening-up period from 1980 to the end of 20th century. Along with the drive of economic globalization and regional cooperation, development of international rivers was thriving, which filled blanks in the research and narrowed gaps with international standards. Relevant studies also provided national and local governments with important scientific grounds for making decisions; 3) since the start of the 21st century, China has integrated its international river studies across sectors and across international borders. Now both government and scientific institutions pay great attention to transboundary environmental issues.

Research progress on international rivers in Asia

With the regional population growth, socioeconomic development, more and more attention has been paid to issues on the shared water allocation and the transboundary eco-security conservation during the development of water resources in the international rivers. In this paper, the existing major problems on transboundary waters in different sub-regions of Asia, such as water shortage, transboundary waters pollution, fragile eco-environment are discussed. Then, the key scientific issues to be concerned in the next study progress on the basis of the analyses of the new research directions and focus fields are raised： （1） unpredicted changes of the hydrologic and water system, and their impacts on the allocation of the sharing waters by global changes; （2） models of the international cooperation on the international rivers on the studies of international and national water laws or regulations, policies, the relative experiences and the case studies; （3） quantificational assessment on environmental flow, available water, and the comprehensive functions and values of the international watercourse system; （4） studies on transboundary aquatic bio-diversity maintenance, transboundary pollution supervision and treatment under the rules and principles accepted by the riparian states; （5） issues on transboundary compensation at the rules of ＂payments for using＂, ＂payments for harm＂ and ＂compensation for benefit＂; （6） using advanced 3S techniques to promote the integrated watershed development and management; and so on.

Equitable utilisation and effective protection of sharing transboundary water resources: international rivers of western China

Western China includes 12 provincial divisions (the 7 provinces of Sichuan, Guizhou, Yunnan, Shaanxi, Gansu, Qinghai and; 5 autonomous regions of Tibet, Ningxia, Xinjiang, Inner Mongolia and Guangxi; and one city of Chongqing), which comprise 71.4% of the national land area, 28.5% of the national population and produce 17.5% of the national GDP in China. There are 17 countries that have riparian relationships with western China, most of which are water-short countries. All are listed by UN ESCAP as countries with potential water crisis. The co-operative development and coordinated management of international rivers in western China is an important step toward the implementation of the national Great Western Development program. Taking into account of the national strategy and object hierarchy, as well as the development demand of the western region, it is necessary to pursue the multi-disciplinary study of the equitable allocation, utilisation, and eco-environment protection of transboundary water resources in the region. Such efforts will undoubtedly provide scientific evidence and support for the decision-making of the environmental protection and ecological construction and management in the western regions, the enforcement of the sub-regional economic co-operation, mitigation of trans-boundary conflicts, and enhancing bio-diversity conservation.

Southwest China and Southeast Asia: towards sustainability through cooperative development and management of international rivers

The western part of China borders on South and Southeast Asia. Of the numerous well known international rivers sharing with the two regions, the Lancang Mekong River has been most extensively studied in the world for its important strategic position, rich resources, prosperous potential market as well as considerable opportunities for investment and development. The sustainable multipurpose development in this area has increasingly become the focus of international regional cooperation, and great attention has been paid to this area by the international society. Up to now, at least 10 major actions in the international regional cooperation are expected in this area. This paper intends, at the angle of geography and with the overall target of promoting the sustainable development in the basin through international cooperations, to study the international position, the potential and the prospects for development of the Lancang Mekong River, to analyze the main problems in this international cooperation, to propose targets and prospects for such cooperation, and to indicate the way for geographers to participate in such research.

Beijing Star River:An Elegant-Distinguished Pet Stone(International Marketing Masters Make Marketings for Beijing Star River)

Star River(or Star Bay), an elite works of Hong Yu Group, is located in Sijixinghe Road, Chaoyang Beilu,Beijing. It is a distinguished residence area, occupyingland of 300 thousand sq. meters. The north side is a for-est garden with 1600 or more mu, the eastern side is agreen belt with 2000-more mu.With an investment of RMB1.5 billion, Beijing StarRiver provides a beautiful landscape and high-qualityresidence. In order to realize a high harmony of con-struction and environment, Beijing Star River has in-vested millions into environmental construction.Star River has won a reputation of Detailed Qualityby Milton Kotler, a world famous marketing master. "Iwould start marketing the apartments in Los Angles, inNew York city, in Chicago, London, " Milton said.One day in September, brothers Kotler(Milton Kotlerand Philip Kotler), world famous marketing masters wereinvited to Star River as noble guests. Their praise forStar River were so high that people would prefer to takeit as an artistic job rather than a residence.

Spatiotemporal variation of snow cover and its relationship with temperature and precipitation in the Yarlung Tsangpo-Brahmaputra River Basin

The snow cover over the Qinghai-Tibet Plateau(QTP)and its surrounding areas is very sensitive to climate changes.Due to the complexity of geographical environment in this large region,the response of snow cover to climate change should exhibit spatiotemporal differences.In this study,the spatiotemporal variations of snow cover from 2002-2015 in the Yarlung Tsangpo-Brahmaputra River Basin(YBRB)were analyzed using an optimized fractional snow cover(FSC)product derived from Moderate Resolution Imaging Spectroradiometer(MODIS).Additionally,the effects of temperature and precipitation on the variability of snow cover were also investigated.The results showed that:(1)The snow cover exhibited large spatial and temporal heterogeneity in the YBRB.High FSC was observed in the northeast of the basin and the south slope of Himalaya,while the lowest was concentrated in the broad valley of the upstream of YBRB.The FSC value reached its highest in winter and dropped to its lowest in summer,but the monthly change processes were different between upstream and downstream regions.(2)A slightly increasing tendency(3.76%/10 a)of snow cover was observed on basin-wide,but the changes varied through time and space.The FSC increased significantly in the source and midstream regions during winter to spring(10.5%-18.0%/10 a),while it changed slightly in summer over all parts of the basin(-0.4%-4.3%/10 a).(3)The study area generally became warm and wet,and the change trend of temperature was more significant than that of precipitation.Snow cover changes were weakly correlated with temperature in winter and precipitation in summer.But in spring and autumn,both precipitation and temperature were significantly related to snow cover change in most regions of the basin.(4)The dominant factor driving the changes of snow cover varied in seasons.The area dominated by temperature was slightly larger than that dominated by precipitation in spring,except that precipitation significantly dominated the snow cover changes in the source region;In summer and autumn,temperature contributed more to the snow cover change in most areas of the basin;However,in winter,precipitation played a leading role in the variations of snow cover.These findings help to understand the different performance of the snow cover in the QTP and its surrounding areas under future climate change.

Past and Future Changes in Climate and Water Resources in the Lancang–Mekong River Basin: Current Understanding and Future Research Directions

The Lancang–Mekong River(LMR)is an important transboundary river that originates from the Qinghai–Tibet Plateau,China and flows through six nations before draining into the South China Sea.Knowledge about the past and future changes in climate and water for this basin is critical in order to support regio-nal sustainable development.This paper presents a comprehensive review of the scientific progress that has been made in understanding the changing climate and water systems,and discusses outstanding challenges and future research opportunities.The existing literature suggests that:①The warming rate in the Lancang–Mekong River Basin(LMRB)is higher than the mean global warming rate,and it is higher in its upper portion,the Lancang River Basin(LRB),than in its lower portion,the Mekong River Basin(MRB);②historical precipitation has increased over the LMRB,particularly from 1981 to 2010,as the wet season became wetter in the entire basin,while the dry season became wetter in the LRB but drier in the MRB;③in the past,streamflow increased in the LRB but slightly decreased in the MRB,and increases in streamflow are projected for the future in the LMRB;and④historical streamflow increased in the dry season but decreased in the wet season from 1960 to 2010,while a slight increase is projected during the wet season.Four research directions are identified as follows:①investigation of the impacts of dams on river flow and local communities;②implementation of a novel water–energy–food–ecology(WEFE)nexus;③integration of groundwater and human health management with water resource assessment and management;and④strengthening of transboundary collaboration in order to address sustainable development goals(SDGs).

Great Progress Achieved on Scientific Survey and International Cooperation along the Lancang-Mekong River

Scientific Survey on the middle-and lower-reaches of Lancang-Mekong River and Grand Shangri-La Area is a key project of national scientific infrastructure programme funded by Ministry of Science

大尺度跨境流域径流预测的迁移学习框架--敏感性分析及在数据稀缺流域的适用性

The imbalance in global streamflow gauge distribution and regional data scarcity,especially in large transboundary basins,challenge regional water resource management.Effectively utilizing these limited data to construct reliable models is of crucial practical importance.This study employs a transfer learning(TL)framework to simulate daily streamflow in the Dulong-lrrawaddy River Basin(DIRB),a less-studied transboundary basin shared by Myanmar,China,and India.Our results show that TL significantly improves streamflow predictions:the optimal TL model achieves an average Nash-Sutcliffe efficiency of 0.872,showing a marked improvement in the Hkamti sub-basin.Despite data scarcity,TL achieves a mean NSE of 0.817,surpassing the 0.655 of the process-based model MIKE SHE.Additionally,our study reveals the importance of source model selection in TL,as different parts of the flow are affected by the diversity and similarity of data in the source model.Deep learning models,particularly TL,exhibit complex sensitivities to meteorological inputs,more accurately capturing non-linear relationships among multiple variables than the process-based model.Integrated gradients(IG)analysis furtherillustrates TL's ability to capture spatial het-erogeneity in upstream and downstream sub-basins and its adeptness in characterizing different flow regimes.This study underscores the potential of TL in enhancing the understanding of hydrological processes in large-scale catchments and highlights its value for water resource management in transboundary basins under data scarcity.

Glacier area changes in the Nujiang-Salween River Basin over the past 45 years

Automated image classification and visual interpretation of Landsat imagery were used to extract the glacier boundary in the Nujiang-Salween River Basin(NSRB)around the years 1975,2000,and 2020.The spatiotemporal characteristics of glacier area changes in the NSRB were determined and the reasons for the spatial heterogeneity in glacier area changes were discussed,based on comparative analyses of temperature and precipitation data from meteorological stations around the NSRB.The results indicate that 1)the total glacier area in the NSRB decreased by 477.78 km^(2)(28.17%)at a rate of-0.62%/a in 1975-2020.Most shrinkage occurred at low and mid altitudes,with the most severe occurring at 5290-5540 m,accounting for 40%of the total shrinkage.Considering other river basins in China,the relative glacier area change rate in the NSRB was similar to that for typical inland river basins in northwest China but lower than that for other transboundary river basins in the southeastern Tibetan Plateau.2)These areal changes in the NSRB presented obvious regional differences.The glaciers in the Hengduan Mountains retreated significantly,followed by those in the Nyainqentanglha Mountains,with relatively low shrinkage observed in the Tanggula Mountains.The number of cold and hot spots indicating areal changes increased after 2000,along with their spatial heterogeneity.3)The glacier shrinkage rate over different time intervals was positively correlated with temperature.Thus,spatial heterogeneity of climate change effects could elucidate differences in the glacier area change rate in different regions of the NSRB.The temperature rise was determined as the primary reason for the significant glacial retreat over the past 45 years.As the significant warming trend continues,the glacier area in the NSRB is likely to shrink further.

Mini-review on river eutrophication and bottom improvement techniques, with special emphasis on the Nakdong River

Water quality in rivers is vital to humans and to maintenance of biotic and ecological integrity.During the Four Major Rivers restoration of South Korea, remarkable attempts have been made to decrease external nutrient loads and moveable weirs were designed to discharge silt that may deposit in pools. However, recently eutrophication of the Nakdong River, which was limited to the lower reaches, is seen to be spreading upstream. The reduction of external nutrient loads to rivers is a long-term goal that is unlikely to lead to reductions in algal blooms for many years because of the time required to implement effective land management strategies. It would therefore be desirable to implement complementary strategies. Regulating the amount of water released is effective at preventing algae blooms in weir pools; so, the relationship between discharge, stratification and bloom formation should be understood in this regard. However, pollutants are likely to accumulate in the riverbed upstream from release points. Thus, to control phosphorus levels, total phosphorus density should be lowered by applying in-river techniques as well. As many ecosystem properties are controlled by multiple processes, simultaneous river bottom improvement techniques, such as combined dissolved oxygen supply and nutrient inactivation, are likely to be effective. The purpose of this review is to present a series of technological approaches that can be used to improve the river bottom area and hence sediment nutrient release, and to illustrate the application of these techniques to the Nakdong River.