Lancang-Mekong River Basin Research Articles

Changes in the Lake Area of Tonle Sap: Possible Linkage to Runoff Alterations in the Lancang River?

Tonle Sap Lake is the largest freshwater lake in Southeast Asia. Water development infrastructures are increasingly being constructed in the Lancang–Mekong River Basin, which is a major concern considering its potential impact on Tonle Sap Lake. This study aimed to investigate variations in the area of the lake and discuss their possible linkage to runoff alterations in the Lancang River (Upper Mekong) by comparing runoff at the Yunjinghong hydrological station before and after significant changes in runoff trends that occurred in 2008. First, four commonly used water body extraction methods (MNDWI, NDWI, NDVI, and EVI) were compared and MNDWI was found to provide a better and more stable performance. Based on MOD09A1 data, MNDWI was used to extract the water area of the lake from 2000 to 2014, and characteristics of variations in the area before and after 2008 were analyzed. The water area of Tonle Sap Lake displayed an overall decreasing trend, and specifically decreased by 8.3% during the flood season and by 1.5% on average during the dry season after 2008. Seasonal variations in the water area of Tonle Sap Lake were dominantly influenced by runoff from the Mekong River. Compared with the period 2000–2007, runoff at Yunjinghong station were increased during the dry season (20.74%) and decreased during the flood season (34.25%) between 2008 and 2014. Changes in upstream runoff contributed to runoff at the Stung Treng station in the lower Mekong River by 6.17% (dry season) and −2.41% (flood season). Evidently, the operation of dams in the Lancang River does not primarily account for the area decrease of Tonle Sap Lake during the flood season. In contrast, runoff increase during the dry season mitigates the area decrease of Tonle Sap Lake to a certain extent.

Analysis of spatial-temporal variation in NPP based on hydrothermal conditions in the Lancang-Mekong River Basin from 2000 to 2014.

Against the background of global climate change, spatial-temporal variation in net primary productivity (NPP) has attracted much attention. To analyze NPP spatial-temporal variation within the context of changes in hydrothermal conditions, the Vegetation Photosynthesis Model (VPM) is used to elucidate the mathematical relationship between NPP and hydrothermal conditions. Based on this spatial-temporal pattern of NPP and hydrothermal conditions in the Lancang-Mekong River Basin, regression statistics, an empirical model of land evaporation, and the water and thermal product index (K) are used to evaluate correlations between NPP and hydrothermal conditions in terms of their distribution pattern and interaction. The results show the following. (1) From 2000 to 2014, NPP in the Lancang-Mekong River Basin was highest in the central region and gradually decreased toward the southwest and northwest, whereas the annual change rate in NPP showed no significant increasing trend. (2) In the Lancang Basin, the correlation between hydrothermal conditions and NPP was high with respect to their distribution patterns, though this correlation was low in the Mekong Basin. (3) Correlation between K and NPP is high in the region where the effects of water and thermal factors on vegetation growth are similar. (4) K is an effective complement to the correlation between a single hydrothermal factor (temperature or precipitation) and NPP, and the influence of hydrothermal conditions on NPP was positive in the Lancang River and negative in the Mekong River Basin. Our study quantitatively analyzes the spatial-temporal correlation between NPP and hydrothermal conditions. The findings can reflect the vegetation change tendency and provide scientific data for ecological environment development and protection in the study area.

Dam Construction in Lancang‐Mekong River Basin Could Mitigate Future Flood Risk From Warming‐Induced Intensified Rainfall

AbstractWater resources management, in particular flood control, in the Lancang‐Mekong River Basin (LMRB) faces two key challenges in the 21st century: climate change and dam construction. A large‐scale distributed Geomorphology‐Based Hydrological Model coupled with a simple reservoir regulation model (GBHM‐LMK‐SOP) is used to investigate the relative effects of climate change and dam construction on the flood characteristics in the LMRB. Results suggest an increase in both flood magnitude and frequency under climate change, which is more severe in the upstream basin and increases over time. However, stream regulation by dam reduces flood risk consistently throughout this century, with more obvious effects in the upstream basin where larger reservoirs will be located. The flood mitigation effect of dam regulation dominates over the flood intensification effect of climate change before 2060, but the latter emerges more prominently after 2060 and dominates the flood risk especially in the lower basin.

Identifying trace metal distribution and occurrence in sediments, inundated soils, and non-flooded soils of a reservoir catchment using Self-Organizing Maps, an artificial neural network method.

The Lancang-Mekong River is a trans-boundary river which provides a livelihood for over 60 million people in Southeast Asia. Its environmental security is vital to both local and regional inhabitants. Efforts have been undertaken to identify controlling factors of the distribution of trace metals in sediments and soils of the Manwan Reservoir catchment in the Lancang-Mekong River basin. The physicochemical attributes of 63 spatially distributed soil and sediment samples, along with land-use, flooding, topographic, and location characteristics, were analyzed using the Self-Organizing Map (SOM) methodology. The SOM permits the analysis of complex multivariate datasets and gives a visual interpretation that is generally not easy to obtain using traditional statistical methods. Across the catchment, enrichments of trace metals are rare overall, despite the severely enriched cadmium (Cd). The analysis of SOM showed that flooded levels and land-use types were associated with high concentrations of Cd. Sediments and inundated soils covered with shrub and open woodlands in downstream always have a high concentration of Cd. The results demonstrate that SOM is a useful tool that can aid in the interpretation of complex datasets and help identify the environment of enriched metals on a catchment scale.

Lancang-Mekong River Cooperation and Trans-Boundary Water Governance: A Chinese Perspective

Water is a strategic resource for life and the development of all nations, thus water security governance has been an issue of vital importance to countries, especially those which do not have guaranteed sources of potable water. The Lancang-Mekong Cooperation (LMC) mechanism, which focuses on water resources cooperation along the Lancang-Mekong River, serves as a good example. The current features of water security governance in the Lancang-Mekong River Basin indicate the necessity and importance of the LMC mechanism. Against the background of climate change and deficiency in governance capacity, all the Lancang-Mekong countries should concentrate on water security governance in the region. China, in particular, should continue to practice the Asian Security Concept in order to serve its Belt and Road Initiative (BRI) and its vision to build a community of shared future with neighboring countries.

Sensitivity of the Penman-Monteith reference evapotranspiration to sunshine duration in the Upper Mekong River Basin

ABSTRACTSensitivity analysis is important in understanding the relationship between sunshine duration (SD) and reference evapotranspiration (ETref). This study was developed in the Lancang-Mekong River Basin using a non-dimensional relative sensitivity coefficient (SN) relating ETref to SD. The SN for January and July for each station were calculated. The results indicate that (a) the SD and SN change in similar ways, where January and July are selected as two representative time slices; (b) the spatial distributions of the long-term averaged SN for January and July are the reverse of each other; (c) the most abrupt changes in climate occur in the 1980s and the middle region is sensitive to climate change; and (d) periodicities of 2–4 and 14–16 years are detected in the basin generally. The significant increase of inter-decadal filter variance indicates changes in the long-term memory of the local climate system.EDITOR Z.W. KundzewiczASSOCIATE EDITOR not assigned

Effects of damming on the biological integrity of fish assemblages in the middle Lancang-Mekong River basin

The Lancang-Mekong River basin contains a diverse assemblage of freshwater fish species; however, their populations are threatened by current and planned dam construction along the river. Fish assemblages are sensitive indicators of environmental degradation and can be used to assess aquatic ecosystem health. This research compared the fish fauna at the Xiaowan hydropower dam located on the middle reaches of the Lancang-Mekong River at three time periods: in 2008 (before impoundment), 2010 (water storage) and 2011 (full operation). A modified fish index of biological integrity (modified F-IBI) was developed and it synthesized information on the taxonomic composition, trophic guilds, and tolerance levels of the fish and habitat diversity to quantitatively assess the condition of fish populations before and after damming. This index also was used to assess the longitudinal diversity of the fish fauna along the river channel and could assess the barrier effect associated with the dam. Jaccard's index of similarity was used as a feasible tool to assess fish diversity loss and biotic homogenization. The analysis clearly showed a homogenization of the fish communities after damming, and the reservoir impoundment region showed much more serious homogenization than the downstream region. The Xiaowan dam had an immediate and profound effect on the fish fauna in this region of the Lancang-Mekong River. A total of eight cascading dams are planned for development in this region, and, unless conservation mitigation efforts are considered, the results could be devastating on the native fish populations of middle reaches of the Lancang-Mekong River basin.

Effects of cascade hydropower dams on the structure and distribution of riparian and upland vegetation along the middle-lower Lancang-Mekong River

The extensive number of hydropower dams being planned in southwest China has attracted much attention in recent years. Eight cascading dams along the middle and lower reaches of the Lancang-Mekong River basin were selected to assess the riparian and upland vegetation. A total of 24 transects and 126 quadrats perpendicular to the river channel were surveyed from upstream to downstream. By using two-way indicator species analysis (TWINSPAN), the vegetation types in this region were classified into 21 vegetation classes. The ecological gradient analysis was completed using canonical correspondence analysis (CCA) and demonstrated that the dominant environmental factors impacting vegetation distribution were the variations in latitude and altitude. The vegetation impact index (VII) was developed as a quantitative index to assess the impact of dam inundation and operation on the upland and riparian vegetation. The values of VII showed that the most endangered vegetation communities were the shrub and herb communities in riparian habitats along this river. The effects of cascading hydropower dams on riparian and upland vegetation distribution were more complex than those of single dams. Cascading hydropower dams can enhance habitat fragmentation, reduce the distribution ranges (latitude and altitude) of primary vegetation and reduce the complexity of the vegetation types along the river as well as induce the loss of primary vegetation in the whole watershed.

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.

Risk Analysis of Water Resources Crisis in the Lancang - Mekong River Drainage Basin under the Background of Climate Change

Aiming at the deteriorating variation trends and potential crisis of water resources in the Lancang-Mekong River Basin under Climate Change, from the view of risk analysis, a conceptual framework of tropical cyclone disaster risk is established, an assessment index system of water resources crisis risk in Langcang-Mekong River Basin are explored based on the thought of AHP, and using the risk index assessment method, an assessment index system is established. Then, the risk assessment of water resources crisis in the Lancang - Mekong River Basin under Climate Change is carried out.

Analysis on Equitable and Reasonable Allocation Models of Water Resources in the Lancang-Mekong River Basin

In this paper, according to the basic rule of the equitable and reasonable utilization of water resources in international rivers, the normal approaches of resolving the conflicts over water and the basic models of water allocation are introduced. The tendency and the problems of water utilization among the riparian states in Lancang-Mekong River are discussed. The extent of cooperation and the conditions of the management institution of the river basin are analyzed. In the present situation, it is considered that the basin-wide allocation model of water resources is the best one in Lancang-Mekong River.