Soil and water loss in the Lancang River-Mekong River watershed (in Yunnan section, China) and its control measures

According to a lot of hydrological and environmental monitoring data, the condition of soil and water loss in the Lancang River Mekong River watershed (in Yunnan section, China) is described. The occurrence and development of soil and water loss is analyzed. The conclusion is that: (1) generally, the situation of soil and water loss in the Lancang River Mekong River watershed (in Yunnan section, China) is light, however, soil and water loss in some regions is serious, especially in the middle reach area of the river; (2) soil and water loss in the Lancang River Mekong River (in Yunnan section, China) watershed presents developing tendency and it is mainly caused by human beings. In accordance with these results, the control measures for soil and water loss are discussed.

Meteorological Drought in Nujiang and Lancang River Basins during Recent 50 Years

Drought is one of the main natural disasters that cause economic loss in the basins of international rivers such as Nujiang and Lancang rivers. Based on the monthly precipitation and temperature data of 31 meteorological stations in Nujiang and Lancang river basins in Yunnan Province during 1965-2013, the standardized precipitation evapotranspiration index(SPEI) in each of the two bio-climate zones was calculated. In addition, the drought process in annual, seasonal and monthly scale was analyzed respectively to reveal the spatial and temporal characteristics and the intensity variation of meteorological drought in Nujiang and Lancang river basins in Yunnan Province. The results showed that there was a significant increasing trend in seasonal(especially winter's) and monthly drought since the late 1970 s; the drought occurred in the two bio-climate zones showed no obvious spatial distinction, and it was synchronized with that occurred throughout Yunnan Province; and in the recent 50 years, the significant increase of drought in the study area may be attributed to the significant rise in temperature, rather than the slight decline of the precipitation.

Projection of temperature change and extreme temperature events in the Lancang–Mekong River basin

The Lancang–Mekong River basin(LMRB) is under increasing threat from global warming. In this paper, the projection of future climate in the LMRB is explored by focusing on the temperature change and extreme temperature events. First, the authors evaluate the bias of temperature simulated by the Weather Research and Forecasting model. Then, correction is made for the simulation by comparing with observation based on the non-parametric quantile mapping using robust empirical quantiles(RQUANT) method. Furthermore, using the corrected model results, the future climate projections of temperature and extreme temperature events in this basin during 2016–35, 2046–65, and 2080–99 are analyzed. The study shows that RQUANT can effectively reduce the bias of simulation results. After correction, the simulation can capture the spatial features and trends of mean temperature over the LMRB, as well as the extreme temperature events. Besides, it can reproduce the spatial and temporal distributions of the major modes. In the future, the temperature will keep increasing, and the warming in the southern basin will be more intense in the wet season than the dry season. The number of extreme high-temperature days exhibits an increasing trend, while the number of extreme low-temperature days shows a decreasing trend. Based on empirical orthogonal function analysis, the dominant feature of temperature over this basin shows a consistent change. The second mode shows a seesaw pattern.

FACILITATING REGIONAL SUSTAINABLE DEVELOPMENT THROUGH INTEGRATED MULTI-OBJECTIVE UTILIZATION, MANAGEMENT OF WATER RESOURCES IN THE LANCANG-MEKONG RIVER BASIN

The Lancnag Mekong River is the most important international river across China and Southeast Asia, If it is developed according to 'Great Mekong Subregional Cooperation Plan' [9] prepared by ADB, the area directly affected will be up to over 2.32 million km 2, the population over 220 million, and the natural environment, and socio-economic conditions within a large area will be greatly changed. 'Agreement on Cooperation for Sustainable Development of Mekong Basin' signed by the four riparian countries along the lower Mekong River on April 5, 1995 provides a new opportunity for sustainable development of the Basin. According to preliminary analysis, if the multipurpose utilization of the water resources is the target for carrying out integrated planning and management, and the efforts are made 1) to focus on energy exploitation on the Lancang River Mainstream and the tributaries of the lower Mekong River; 2) to build gated weirs at Tonle Sam; 3) to construct spillways at the Mekong Delta; 4) to facilitate flood dykes in big cities and on both banks of the mainstream which are concentrated with population and farmland and liable to be flooded, and 5) to strengthen networks for forecasting hydrological and meteorological conditions, then all problems such as power demand, irrigation, flood, salt water intrusion as well as acid water erosion to soil could be solved without constructing large cascaded stations and dams on the lower Mekong Mainstream. This will not only avoid input of great number of fund, large scale resettlement and land inundation, but also prevent aquatic organisms living in Mekong River from being injured due to dam construction, and promote the sustainable development of the Basin.

Groundwater status and associated issues in the Mekong-Lancang River Basin： International collaborations to achieve sustainable groundwater resources

Groundwater is an important and readily available source of fresh water in the Mekong-Lancang River Basin. With a rapid population growth and increasing human activities, an increasing number of countries in the Mekong-Lancang River Basin are experiencing depleted and degraded groundwater supplies. In transboundary river basins, such as the Mekong-Lancang River, prioritizing the use of the shared aquifer by one riparian government may affect the opportunities of other riparian governments and lead to potential water conflicts between neighboring countries. To promote the sharing of strategies and information for the sustainable and equitable use of water resources of the shared basin, international collaborative workshops on groundwater resources have been organized for all Mekong-Lancang River countries. These workshops provide an opportunity to communicate and discuss nationally sensitive issues on groundwater by the associated countries, with topics covering multiple aspects of groundwater, such as the groundwater status in the basin, quality issues, water use conflicts, hydrological information gaps, management policies and capacity building for successful water resource management. Consensus has been reached by all countries on the importance of catchment-based groundwater management and the need for close communication among the countries. Strategies for managing transboundary aquifer issues must foster international collaboration based on the regional network, influence national networks and enhance the capacity to building maps and monitoring systems based on associated databases. The sustainability of water resources cannot be achieved without the integrated involvement and contributions by multiple countries and various stakeholders. Therefore, collaborative workshops provide a great opportunity to further our understanding of the hydrologic processes of the Mekong River Basin, share the benefits of the aquifer and provide a strategy and vision for sustainable water resource management in the Mekong-Lancang River countries.

Water Cooperation Priorities in the Lancang-Mekong River Basin Based on Cooperative Events Since the Mekong River Commission Establishment

The Lancang-Mekong River has attracted much attention from researchers, but the cooperation on water issues in this river basin has been limited, even after the establishment of the Mekong River Commission(MRC). Cooperation on water resources has been determined as one of the key priority areas in the Lancang-Mekong Cooperation Mechanism, but there are no details of targets. In order to establish the priorities of water cooperation under the mechanism, we adopted nine categories to classify the objectives of 87 water cooperation events based on the ‘Lancang-Mekong Water Cooperative Events Database' from 1995 to 2015. Based on the occurrence of cooperative events, cooperative objectives, cooperative scales, and approaches to cooperation, we conducted statistical, correlation, and text analyses. Our analyses indicated the following results: under the impact of economic conditions inside and outside the river basin, full cooperation appeared more difficult than bilateral and multilateral cooperation. Each of the partners adopted different preferences for cooperation targets. Cooperation with more definite objectives was easier to establish than cooperation with broader and more complex objectives. The potential objectives for water cooperation were navigation, hydropower, joint management, data sharing, flood control and water use. Because hydropower development is controversial, and because water cooperation is avoided by most existing regional cooperation mechanisms due to its complexity, we suggest the following priority areas for water cooperation in the Lancang-Mekong River Basin. 1) Navigation and flood control/drought relief are attractive objectives for all the riparian countries across the whole watershed. 2) Data sharing should be a priority for cooperation in the watershed due to its laying the foundation for the equitable and reasonable utilization of transboundary waters. 3) Hydropower is an objective best implemented mainly through bilateral cooperation, and on tributaries.

Hydrological Simulation Using TRMM and CHIRPS Precipitation Estimates in the Lower Lancang-Mekong River Basin

Satellite-based products with high spatial and temporal resolution provide useful precipitation information for data-sparse or ungauged large-scale watersheds. In the Lower Lancang-Mekong River Basin, rainfall stations are sparse and unevenly distributed, and the transboundary characteristic makes the collection of precipitation data more difficult, which has restricted hydrological processes simulation. In this study, daily precipitation data from four datasets(gauge observations, inverse distance weighted(IDW) data, Tropical Rainfall Measuring Mission(TRMM) estimates, and Climate Hazards Group InfraRed Precipitation with Stations(CHIRPS) estimates), were applied to drive the Soil and Water Assessment Tool(SWAT) model, and then their capability for hydrological simulation in the Lower Lancang-Mekong River Basin were examined. TRMM and CHIRPS data showed good performances on precipitation estimation in the Lower Lancang-Mekong River Basin, with the better performance for TRMM product. The Nash-Sutcliffe efficiency(NSE) values of gauge, IDW, TRMM, and CHIRPS simulations during the calibration period were 0.87, 0.86, 0.95, and 0.93 for monthly flow, respectively, and those for daily flow were 0.75, 0.77, 0.86, and 0.84, respectively. TRMM and CHIRPS data were superior to rain gauge and IDW data for driving the hydrological model, and TRMM data produced the best simulation performance. Satellite-based precipitation estimates could be suitable data sources when simulating hydrological processes for large data-poor or ungauged watersheds, especially in international river basins for which precipitation observations are difficult to collect. CHIRPS data provide long precipitation time series from 1981 to near present and thus could be used as an alternative precipitation input for hydrological simulation, especially for the period without TRMM data. For satellite-based precipitation products, the differences in the occurrence frequencies and amounts of precipitation with different intensities would affect simulation results of water balance components, which should be comprehensively considered in water resources estimation and planning.

The evaluation of TRMM tion Analysis （TMPA） in the Lancang River Basin Multisatellite Precipitadrought monitoring in

Drought is one of the most destructive disasters in the Lancang River Basin, which is an ungauged basin with strong heterogeneity on terrain and climate. Our validation suggested the version-6 monthly TRMM multi-satellite precipitation analysis （TMPA; 3B43 V.6） product during the period 1998 to 2009 is an alternative precipitation data source with good accuracy. By using the standard precipitation index （SPI）, at the grid point （0.25°×0.25°） and sub-basin spatial scales, this work assessed the effectiveness of TMPA in drought monitoring during the period 1998 to 2009 at the 1-month scale and 3-months scale; validated the monitoring accuracy of TMPA for two severe droughts happened in 2006 and 2009, respectively. Some conclusions are drawn as follows. （1） At the grid point spatial scale, in comparison with the monitoring results between rain gauges （SPIlg） and TMPA grid （SPIls）, both agreed well at the 1-month scale for most of the grid points and those grid points with the lowest critical success index （CSI） are distributed in the middle stream of the Lancang River Basin. （2） The same as SPIls, the consistency between SPI3s and SPI3g is good for most of the grid points at the 3-months scale, those grid points with the lowest were concentrated in the middle stream and downstream of the Lancang River Basin. （3） At the 1-month scale and 3-months scale, CSI ranged from 50% to 76% for most of the grid points, which demonstrated high accuracy of TMPA in drought monitoring. （4） At the 3-months scale, based on TMPA basin-wide precipitation estimates, though we tended to overestimate （underestimate） the peaks of dry or wet events, SPI3s detected successfully the occurrence of them over the five sub-basins at the most time and captured the occurrence and development of the two severe droughts happened in 2006 and 2009. This analysis shows that TMPA has the potential for drought monitoring in data-sparse regions.

Comparison of spatial-temporal distribution characteristics of water temperatures between Lancang River and Mekong River

水温度(WT ) 是水身体物理性质的重要指示物之一。在河连续统在 WT 上理解空间时间的变化的特征将帮助开发合理 river-water-resource 利用，以避免可能的生态学危机，并且在深奥区域充分利用自然资源计划。作为在亚洲的最大的国际河连续统， Lancang 湄公河河分区(作为更大的湄公河分区知道，公克) 成为了著名经济、政治、生态的自然领土。这研究检验了 Lancang 河水的空间时间的分发特征。温度，用从 11 的 WT 价值的观察数据，水文学在 1960 年代驻扎。而且， Yunjinghong 水文学之间的 WT 差别驻扎(在中国的一个代表性的车站) 并且 Chiang Saen 水文学车站(在泰国的一个代表性的车站) 被分析。结果显示了那：1 ) 水温度比上面的部分在河连续统的更低的部分是更高的。纬度变化是主要影响因素。这效果比在雨季在旱季是更明显的，在冬季更明显比在夏天，和平均最小的 WT 明显的更多比平均最大的 WT ， 2 )之间的 WT 差别上面并且河连续统的更低的部分在研究时期期间由于更低的部分( Chiang Saen 水文学车站)的上面的部分( Yunjinghong 水文学车站)和 WT 的明显的减少的 WT 的小增加是减少。因此， WT 的参数被纬度影响，并且Lancang湄公河河连续统躺在纵贯的方向因此热带水的动物例如热带水的鱼，不能在冬季季节在这河连续统的上面的部分幸存，当时在里面夏天季节，热带水的动物适当地游泳到上面的溪流。更低的湄公河河里的水温度被地区性的水温度和地区性的气候变化主要影响。

Changes in the sediment load of the Lancang-Mekong River over the period 1965-2003

Changes in the sediment load of a river can have important impacts on river channel evolution,nutrient fluxes,aquatic ecology and delta erosion and sedimentation,and the possibility of changes in the sediment load of the Lancang-Mekong River has attracted increasing concern in recent years.Existing studies present conflicting findings regarding the nature and magnitude of recent changes in the sediment load of the Lancang-Meking River and the authors have attempted to assemble the most reliable data on annual sediment loads for the period 1965-2003,to assess recent trends in the sediment load of the river.The changes in annual sediment load at 7 stations on the river are analyzed.Important sediment contributing areas are found in the reaches between Gajiu and Yunjinghong,Chiang Saen and Luang Prabang and downstream of Nong Khai.The sediment load increased at Gajiu,Yunjinghong and Chiang Saen over the period 1985-1992 because of serious soil erosion caused by the expansion of cultivation,the replacement of natural forest by plantations and land disturbance associated with hydropower dam construction.A marked reduction in sediment load occurred at Gajiu after the impoundment of the Manwan Hydropower dam on the Lancang River,but this reduction was not evident downstream at Yunjinghong and the stations further downstream.Significant increases in sediment load appeared at Mukdahan and Khong Chiam.These contrasting patterns of change reflect the influence of sediment contributions from the intervening catchment areas and channel systems as well as storage and remobilization of sediment from the channel system and the impact of hydraulic works such as irrigation systems.The long term mean annual sediment load of the Mekong River at its mouth is estimated to be ca.145×106ta-1,which is lower than previously reported values and it seems likely that this will be reduced in the foreseeable future.

Projection on precipitation frequency of different intensities and precipitation amount in the Lancang-Mekong River basin in the 21st century

In the Lancang‒Mekong River basin(LMRB),agriculture,dominating the local economy,faces increasing challenges in water supply under climate change.The projection of future precipitation in this basin is essential for understanding the challenges.In this study,the Weather Research and Forecasting(WRF)model was applied to project the LMRB precipitation.Comparing with the historical period(1986e2005),we analyzed the changes of both the projected precipitation amount and the frequency of rainless(<0.1 mm d1),light rain(0.1e10 mm d1),moderate rain(10e25 mm d1),heavy rain(25e50 mm d1),rainstorm(50e100 mm d1),and heavy rainstorm(>100 mm d1)for three periods,namely the near-term(2016e2035),mid-term(2046e2065),and long-term(2080e2099).The results indicate that the precipitation amount during the wet season(AprileOctober)is expected to increase in most areas of the basin for the three periods.As for the precipitation during the dry season(NovembereMarch),an increase is projected in most areas for the near-term,while an increase in the lower reach of the basin and a decrease in the upper and middle reach for the mid-term and long-term.The precipitation reduction is expected to be greatest in Myanmar,Laos,Thailand,and Yunnan province of China for the mid-term.The frequency of precipitation in different intensities has prominent regional and temporal differences.During the wet season,the days of rainless and light rain are expected to decrease in the middle reach,whereas the days of rainstorm and heavy rainstorm increase.This feature is especially strong in southern Thailand,southern Laos and Cambodia in the near-term and in Laos and Thailand for the mid-term and long-term.During the dry season,there are projected increasing rainless days and decreasing days of precipitation for the other intensities in the middle reach,and opposite in the rest area of the basin.These projected precipitation changes have potential various impact in different parts of the basin.The middle reach would likely face increasing flood risks because of more days of rainstorm and heavy rainstorm,as well as more precipitation.Yunnan,Myanmar,Thailand and Laos would probably be the center of drought threatens during the dry season due to the increment of rainless days and the precipitation reduction.Besides,the seawater intrusion during the dry season in the near-term and mid-term would be more serious as a result of the precipitation decrease in southern Vietnam.

Vegetation distribution pattern in the dam areas along middle-low reach of Lancang-Mekong River in Yunnan Province, China

Lancang-Mekong River Basin is one of ecoregions with rich biodiversity and high ecological values in the world. The basin has been strongly affected by human activities, particularly by dam construction. This study was conducted to investigate the vegetation distribution patterns in the dam areas along middle-low reach of the Lancang-Mekong River in Yunnan Province of China, where eight cascade dams have been planned or are being constructed. To identify the vegetation composition and structure, we sampled 126 quadrats along the transects arrayed vertically to both side of river channel from the year of 2004 to 2010. We found that the forest, shrub and grass communities were widely spread along the riverside. In low reach watershed of the Lancang-Mekong River, the dominated vegetations were grasses and shrubs which were severely disturbed by human activity. In middle reach of the Lancang-Mekong River, the dry-hot valley vegetation was found in the low valley. At high altitude, the pine forest and semi-evergreen seasonal forest were found. As a result of dam construction and operation, the structure and compositions of riparian vegetation were strongly changed. Some plants declined or disappeared due to the alteration of their habitats. The protection or restoration interventions are urgently needed to mitigate the risk of vegetation damage associated with dam projects along middle and low reach of the Lancang-Mekong River.

The influence of large dams building on resettlement in the Upper Mekong River

This paper seeks to quantify the social and economic impact of resettlement based on the physiographic element changes post relocation. We focus on communities affected by the Nuozhadu hydropower project, the largest existing hydropower project on the mainstream of the Upper Mekong River. Soil and meteorological data were collected from the Soil Spatial Database and the China Terrestrial Ecological Information Spatial Meteorology Database, while social and economic data were collected via field surveys. We have three major con- clusions： （1） Communities will be relocated to a new climate and new elevation, moving from a north tropical climate zone under 700 m to a subtropical climate zone above 700 m. （2） Physiographic element changes due to relocation will reduce household economic income. After relocation, the annual family income of the Shidaimao group decreased by 62%; the annual family income of the other 5 study groups （Lasa, Hani, Nochangchangyi, Mengsa, and Dawazi） dropped by 65%. （3） Communities relocated across the study township are 61.1% less connected with their former relatives after relocation while family-to-family free labor exchange, a previous community norm, decreased by 91%. China＇s dam resettlement compensation system focuses on the loss of economic resources after relocation. However, this study finds that the physiographic elements of the relocation sites are an important driver of ensuring economic growth and stability after relocation. As a result, we recommend more attention be paid to physiographic continuity when designing relocation models.

Environmental and Human Impacts of Lancang-Mekong Mainstem and Tributary Dams on China, Laos, Thailand, Myanmar, Cambodia, and Vietnam

The Lancang-Mekong River in China, Laos, Thailand, Myanmar, Cambodia, and Vietnam is the soul and heart of mainland Southeast Asia. Over 60 million people depend on the river and its tributaries for food, transportation, water, and other necessities of life. The river supports one of the world’s most diverse fisheries, second only to Brazil’s Amazon River. Lancang-Mekong and tributaries are already heavily dammed primarily in China, Laos, Thailand, and Cambodia, with many more dams planned or under construction. Dams can worsen the impact of periodic droughts in the Lancang-Mekong basin and block the river’s “pulse effect” that spreads water and nutrients needed for fishing and farming onto the floodplains and delta. The headwaters of the Lancang are in China and its waters are considered a national resource. China regards the Lancang, Yangtze and Yellow rivers as a free resource rather than a shared resource. The primary difference between these rivers is the Lancang flows from China into and through other countries and not directly into a sea or ocean. China and Myanmar have not joined the Mekong River Commission (MRC) as full members but have been Dialogue Partners since 1996. Over the past thirty years, China’s Lancang policies and actions have reflected its national resource interests. China has actively engaged with individual transboundary countries at various levels including environmental, conservation, and economic agreements. The primary objective of this study is to assess the environmental and human impacts of all Lancang-Mekong mainstem and tributary dams and the plans by many countries for more hydropower utilizing the potential of the river as the continent’s energy lifeline. Future dams need to include fish ladders and navigation locks to reduce the environmental impacts on fish populations, natural resources, navigation, and livelihoods. Strengthening of international collaboration via the MRC or by individual or multiple country agreements to address Lancang-Mekong’s sustainable transboundary development goals is recommended. When new Lancang-Mekong and tributary dams are built within any of the transboundary watershed countries, additional communities will need to be resettled. Significant environmental and human impacts are observed. Steps will have to be taken by all the concerned countries to prevent these problems and to ensure that people’s livelihoods are restored after resettlement.

Analysis and prediction of sediment trapping efficiencies of the reservoirs in the mainstream of the Lancang River

存储的水和水库套住的沉积在下游的水路环境上导致物理、化学、生态的效果。关于水库沉积的量的研究是钥匙估计它的环境影响。在位于 Manwan 水库的 upstream 和 downstream 的计量车站在 39 年获得的沉积负担数据被用来估计 Manwan 水坝的套住的效率(TE ) 。TE 价值当时与用修改 Brune 和 Siyam 模型的估计相比。结果显示那：(1 ) 计量数据估计的 Manwan 水坝的 TE 是 60.48% ，并且两个都， TE 值由修改 Brune 计算了， Siyam 模型是 60.03% 。近似 TE 价值显示修改 Brune 和 Siyam 模型能被用来在 Lancang 河的主流作为 Manwan 水库与类似的存储能力预报另外的水库的 TE；(2 ) Gongguoqiao， Dachaoshan 和 Jinghong 水坝的 TE 价值是大约 30.23% ， 66.05% 和 63.50% 由修改 Brune 模型估计了，并且 38.81% ， 63.97% 和 62.30% 由修改 Siyam 当模特儿。在论文采用的结果和方法论能也被用来在西南的中国在另外的河盆估计 TE。

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.

基于多维Copula函数的澜沧江-湄公河流域气象干旱特征分析

为全面揭示变化环境下澜湄流域多维气象干旱特征,采用标准化降水蒸散指数SPEI表征流域气象干旱,基于游程理论分别提取澜沧江段和湄公河段上、中、下游流域1901—1960年和1961—2021年两个时段的干旱事件,利用Copula函数分别构建两个时段不同子流域二维和三维干旱特征变量联合分布,计算不同干旱特征变量组合条件下的干旱联合发生概率,对比分析不同子流域多维气象干旱特征的时空变化。结果表明:时间上,1961—2021年各子流域平均干旱程度均较1901—1960年更严峻,尤其是极端干旱事件(单变量累积频率为25%、50%)的多维干旱联合发生概率增幅最大;空间上,1961—2021年,随着干旱历时、烈度和烈度峰值的增加,“或”情况下多维干旱联合发生概率最高值区自北向南转移,“且”情况下多维干旱联合发生概率最高值区自南向北转移。