Search

Recent decades in the Lancang River Basin have witnessed extensive construction of hydropower dams, profoundly impacting the local environment. Utilizing high-precision satellite data, we conducted a comprehensive analysis of vegetation cover and carbon emissions, integrating data-driven time series and spatial analysis models to capture both temporal and spatial dynamics. Our findings reveal that hydropower dam construction in the Lancang River Basin has significantly promoted vegetation restoration and growth, concurrently facilitating a reduction in regional carbon emissions. Employing deep learning models for time-series prediction, we observed a substantial increase in the sum of the local normalized difference vegetation index (NDVI) post-construction, with an average rise of from 16.15% to a maximum of 20.12% during the pivotal hydropower dams' operational phase. Between 2001 and 2020, the construction of hydropower dams in the basin corresponded to notable changes in ecological and carbon metrics. Specifically, vegetation cover expansion intensity (VCEI) reversed from a negative mean of −0.009 to a positive mean of 0.008. Additionally, the carbon emission intensity (CEI) around these dams drastically reduced, shifting from an average of 0.877 to 0.052. Importantly, the Global Moran's I for VCEI significantly increased from 0.288 pre-2016 to 0.679 post-2015, reflecting a stronger spatial autocorrelation in vegetation patterns. Accordingly, these findings illustrate the complex interplay between hydropower dams and environmental outcomes, underscoring the critical role of pivotal hydropower dam construction in ecological improvement. The research results have improved and complemented those of previous studies on the environmental impact of hydraulic engineering, providing valuable insights for the construction management and policy formulation of hydropower dams in other similar river basins around the world. [ABSTRACT FROM AUTHOR]

Environment change alters hydrological rhythms and affects utilization of water resources for a river basin. The Lancang-Mekong River is a transboundary river in Southeast Asia originated in the Southwestern China. It is of significance to scientifically quantifying runoff change attribution of the Langcang River for supporting water benefits share between countries which the Lancang-Mekong River runs across. Based on the recorded runoff data series from 1961 to 2020 gauged at the Yunjinghong hydrometric station on the Langcang River, the variability characteristics of runoff series and the impact of climate change and human activities on runoff change as well as its seasonal distribution were investigated by using statistical methods and hydrological simulation methods. The results show that: ① The measured annual runoff at Yunjinghong station showed a significant decrease trend from 1961 to 2020, with an increase in runoff during the period from January to May and a decrease in runoff in period from June to December. The abrupt change of the measured annual runoff series was occurred in 2008. ② The RCCC-WBM model performs well for monthly natural discharge simulation in the baseline period of 1961-2008 with relative error of less than 1. 0%. The simulated natural annual runoff in the human-disturbance period of 2009-2020 is about 371. 8 mm, which is 6. 8% less than that in baseline period. The reduction is induced by climate change. ③ Reservoirs construction and operation is the utmost human activity in the Langcang River. Human activities are the main reason of runoff decrease in the reservoir impoundment period of 2009-2013, while climate change is principal driver of runoff reduction in in the reservoir operation period of 2014-2020, which contribution is about 61. 7% of total runoff reduction. ④ The reservoirs operation makes runoff decrease by 44. 3% in flood season from June to November and increase by 134. 3% in dry season from December to May for period of 2014-2020. The regulation function of reservoirs on the Langcang River for decreasing flood discharge and increasing low flow has been guaranteeing security of water supply and flood control for the middle and lower reaches of the Mekong River. [ABSTRACT FROM AUTHOR]

Emerging and fragile ecosystems such as reservoir riparian zones are of increasing concern with the increasing number of damming projects worldwide. Current knowledge of riparian vegetation in reservoirs focuses on the individual and community level, with little understanding of spatial patterns and ecological processes at the landscape level. Here, we demonstrate the evolution process, evolution direction, and evolution mechanism of vegetation spatial patterns under persistent and periodic inundation disturbances in the reservoir riparian zone, through coupled analyses of landscape evolution and ecological processes, using continuous years of drone observation data in the riparian zones of two major reservoirs, Xiaowan and Nuozhadu of the Lancang River. We found that vegetation landscape evolution is driven by seed dispersal, environmental factors fluctuations, species tolerance differences, and competition for resource availability, showing a clear trend towards banded evolution. Ecological niche processes such as periodic wet-dry environmental filtering and interspecific competition dominated the formation of vegetation banding patches, and neutral processes of random seed dispersal dominated the areas where banding patches were formed. The water requirements of plants during the exposing period lead to a greater influence of environmental factors that are closely related to water, such as net rainfall, sunshine hours, groundwater storage, and soil moisture. Water redistribution between vegetated and bare ground patches is key to their formation and stability in the upper part of the riparian zone, where drought stress is severe, while in the lower part, vegetation is mainly affected by inundation stress during flooding periods. Therefore, riparian vegetation restoration is critical to maintain a certain area of bare ground patches for drought areas in the exposing period, in contrast to the emphasis on vegetation patch coverage. And it is possible to carry out spatial planning based on the development trend of the belt distribution, taking into account the flood and drought tolerance of the species as well as the fluctuating rhythms of the main factors, such as the rainfall, which is worth exploring further.

Accurate monthly streamflow prediction is crucial for effective flood mitigation and water resource management. The present study proposes an innovative similarity-derived model (SDM), developed based on the observation that similar monthly streamflow patterns recur across different years under comparable hydrological and climate conditions. The model is applied to the Lancang River Basin in China. The model performance is compared with the commonly used support vector machine (SVM) and Mean methods. Evaluation measures such as RMSE, MAPE, and NSE confirm that SDM6 with a reference period of six months achieves the best performance, improving the Mean model by 79.9 m3/s in RMSE, 6.07% in MAPE, and 8.62% in NSE, and the SVM by 53.65 m3/s, 0.24%, and 5.53%, respectively. [ABSTRACT FROM AUTHOR]

[Objective] The ecological network of Natural Reserves in Lancang River basin, Yunnan Province was constructed in order to providing a scientific basis for the ecological security and protection of the basin. [Methods] We constructed a minimum accumulation resistance model of six ecological factors (distance from water, distance from town, vegetation coverage, land use, slope, and elevation). In this model, the city and county-level nature reserves were considered to be the ecological sources. The ecological network of the Lancang River basin was constructed as the least resistance path between different sources, identified as the potential ecological corridor to detect the ecological nodes and ecological fracture points. [Results] A total of 43 ecological sources in the Lancang River basin (mainly in the middle and lower reaches of the basin) were constructed by using the model, with 67 ecological corridors overlapping the main water system of the Lancang River by 59%. Twenty ecological nodes and 41 ecological breakpoints were identified in the ecological network, and these will be used in the optimization and restoration plan of the ecological network and the construction of regional roads in a later period. [Conclusion] According to the distribution characteristics of ecological source areas, ecological corridors, and ecological networks, the number of ecological source areas in the upper reaches of the Lancang River, Weiyuan River basin, and other related areas should be increased. At the same time, the quality of habitats along river banks in the Lancang River basin should also be improved through the use of ecological construction that considers ecological nodes and ecological breakpoints so as to form a complete ecological protection network, alleviate the problem of islanding, and promote the flow of species between ecological sources.

Copyright of Bulletin of Soil & Water Conservation is the property of Bulletin of Soil & Water Conservation Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Optimizing the pattern of land space development and protection as well as improving regional ecological security are significant tasks in the construction of an ecological civilization. The Lancang River Basin is a significant ecological barrier in Southwest China, and its ecological security is critical to the Natural World Heritage Site of "Three Parallel Rivers" and even to Southeast Asia. In this study, the InVEST model and MSPA method were used for the identification of the ecological sources; the resistance surface was corrected by the night light coefficient; and the ecological linkages, pinch points, obstacles, and ecological breakpoints were extracted using the circuit theory to construct the ecological security pattern of the Lancang River Basin. The major study results indicated that: (1) A total of 23 ecological sources were identified in the watershed, covering an area of 9019.56 km2, mostly large-scale irregular patches. (2) A total of 39 ecological corridors were identified in the study area; 15 key corridors, 17 important corridors, and 7 general corridors were extracted based on the gravity model, which together formed a ecological security network for the watershed. (3) Sixteen ecological pinch points, one primary ecological improvement area, twelve secondary improvement areas, and twenty-nine ecological breakpoints were identified in this study. The ecological protection and restoration of different important ecological areas are conducive to the protection of biodiversity and the construction of the ecological security pattern in the Lancang River Basin. [ABSTRACT FROM AUTHOR]

As a major threat to ecosystem functions and national food security, soil erosion also exerts an influence on the water quality in basins and the operation and maintenance of hydropower plants. Existing discussions about trends of soil erosion focus mainly on its variation and mutation over time. Few studies have addressed the spatial mutation of soil erosion and its influence mechanism. In this research, Sen's slope estimation was coupled with a Mann–Kendall model to explore the spatiotemporal distribution, spatial mutation characteristics and influence mechanisms of soil erosion, and conduct a case study on the Middle and Lower reaches of the Lancang River Basin (ML-LRB) in China. There are three main conclusions from this study: (1) During 2000–2019, the annual soil erosion in the ML-LRB variation ranged from 0 to 7.00 × 103 t/(km2·a) with a multi-year mean of 1.53 × 103 t/(km2·a), decreasing year by year from north to south, while an increasing trend began to appear in the central above region after 2015. (2) The areas with decreased soil erosion were much larger than those with increased soil erosion during 2000–2019, and there was a concentrated increase in soil erosion in Dali and in Xishuangbanna. (3) The mutation of the soil erosion intensity was spatially consistent with that of the Normalized Difference Vegetation Index (NDVI). Overall, this paper provides a new perspective for the study of factors affecting the trends and spatial mutation of soil erosion. [ABSTRACT FROM AUTHOR]

Study Region: Lancang River Basin (upper reaches of the Mekong River basin within China). Study Focus: Complex terranes and diverse climates are a bottleneck for understanding the hydrology of rivers originating from the Tibetan Plateau. This study deals with the impact of climate change on water storage in the Lancang River Basin, which is governed by the South Asian monsoon system. We evaluated the spatiotemporal distribution of multi-source precipitation, evapotranspiration, and terrestrial water storage (TWS) to understand the hydrological system in the region. We provide evidence of climate change impacts on TWS and basin discharge over an upstream region of the transboundary river system. New Hydrological Insights for the Region: The Five Gravity Recovery and Climate Experiment (GRACE) products and Global Land Data Assimilation System (GLDAS) TWS display analogous seasonal distribution, even though the amounts differ between them. The GRACE and GLDAS TWS exhibited a significant negative trend in the basin from 2002 to 2016. However, the Center for Space Research (CSR-M) at the University of Texas and the Jet Propulsion Laboratory (JPL-M) mascon solutions concede more severe and much wider TWS reduction than the three spherical harmonic (SH) solutions. In addition, a downward trend was observed for basin discharge over 15 years as a response to climate change (decreased precipitation and increased evapotranspiration). Furthermore, we identified a 2-month time lag between precipitation and TWS, which could be a response to climatic factors along with aquifer properties in a karst dominated region.

Precipitation phase (e.g., rainfall and snowfall) and snow (e.g., snowpack and snowmelt runoff) in high-mountain regions may largely affect runoff generation, which is critical to water supply, hydropower generation, agricultural irrigation, and ecosystems downstream. Accurately modeling precipitation phase and snow is therefore fundamental to developing a better understanding of hydrological processes for high-mountain regions and their lower reaches. The Lancang River (LR, or the Upper Mekong River) in China, among the most important transboundary rivers originating from the Tibetan Plateau, features active dam construction and complex water resources allocation of various stakeholders in Southeast Asian countries under climate change. This study aims to improve precipitation phase and snow modeling for the LR basin with a hydrological model and multisource remotely sensed data. Results show that joint use of the Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature product with high spatial resolution (1 km×1 km) and an air temperature product can more precisely distinguish precipitation phase than air and wet-bulb temperature products in the LR basin. Snowfall and snowmelt were found to be controlled primarily by rainfall and snowfall temperature thresholds in snow modeling. The rainfall and snowfall temperature thresholds derived from the hydrological model through calibration with remotely sensed snowpack at basin scales were considerably lower than those derived from in situ observations. Rainfall and snowfall temperature thresholds derived from in situ observations could lead to the overestimation of snowmelt runoff due mostly to the lack of representation of point-based measurements at basin scales. This study serves as a basis for better modeling and predicting snow for the LR basin and potentially other similar basins globally. [ABSTRACT FROM AUTHOR]

The hydrological model is the primary tool for regional water resources management, allocation, and prediction. However, these models always suffer from large uncertainties from multiple sources. Therefore, it is necessary to conduct an uncertainty analysis before performing hydrological simulation. Sequential Uncertainty Fitting (SUFI-2), Parameter Solution (ParaSol), Generalized Likelihood Uncertainty Estimation (GLUE), and Particle Swarm Optimization (PSO) integrated with the SWAT-CUP software were used to calibrate the Soil and Water Assessment Tool (SWAT) model and quantify the parameter sensitivity and prediction uncertainty of the SWAT in the Lancang River (LR) Basin, which is located in the southwest of China. This model was calibrated and validated using the four algorithms both at the daily scale, and the optimal simulation results derived by the four methods showed that the SWAT model performed well over the Yunjinghong station with Nash–Sutcliffe efficiency coefficient (NSE) and coefficient of determination (R2) values greater than 0.8 both in the calibration (1975 to 1989) and validation (1990 to 2004) periods. Among the four algorithms, the ParaSol algorithm produced the best simulation result at the daily scale with NSE values of 0.89 and 0.90 for the calibration and validation periods, respectively. Furthermore, the ParaSol algorithm has the greatest proportion of simulations (94%) with an NSE greater than 0.5. Parameter sensitivity analysis results demonstrated that the four methods all can be used for parameter sensitivity analysis in streamflow simulation, and they all identified that the base flow factor for bank storage (ALPHA_BNK) and effective hydraulic conductivity in the main channel alluvium (CH_K2) were more sensitive. The uncertainty analysis of model parameters showed that the parameter 95PPU (95% prediction uncertainty) width yielded by the ParaSol algorithm was the smallest compared with that of the other methods, followed by PSO, SUFI-2, and GLUE. The uncertainty analysis of the model simulation indicated that the SUFI-2 and PSO methods can achieve satisfactory results (with P-factor > 0.7 and R-factor < 1.5) at the daily scale; among them, SUFI-2 (P-factor = 0.93, R-factor = 1.17) performed much better than PSO (P-factor = 0.78, R-factor = 1.14). In general, by comparing its evaluation criteria (NSE, R2, RE, P-factor, and R-factor) to other methods, ParaSol stood out as the most efficient tool for model calibration. However, SUFI-2 remains the most robust method to perform uncertainty analysis considering its uncertainties of model structure, model inputs, and parameters. This study provides insight into hydrological simulation of the LR Basin using the appropriate algorithm to calibrate the model and implement the uncertainty analysis. [ABSTRACT FROM AUTHOR]

Abstract Meteorological factors and the hydrologic cycle of the Tibetan plateau (TP) significantly influence the water resource supply, ecology, and social economy of wide downstream areas in Asia. This study evaluates changes in meteorological factors (e.g., precipitation, air temperature, and snowfall) and corresponding responses in the hydrological regime under future climate change scenarios in both the TP and the downstream areas. The Lancang River basin (LRB), located in the southeast TP and known as the upper Mekong River basin, is selected as the case study area. Future climate change projections are derived from five independent GCMs of CMIP5 and their multi-model ensemble. The variable infiltration capacity (VIC) distributed hydrological model is used to generate streamflow projections in future scenarios. Results show that precipitation and air temperature in both the lower LRB (representing the downstream area of TP) and upper LRB (representing the area in TP) are expected to increase substantially in the future, with higher increments in air temperature found in the upper LRB under high-emission scenarios. Snowfall, snow water equivalent (SWE), and snowmelt are commonly found to decrease with increasing air temperature, and the snow melt time tends to be earlier. Significantly increasing mean and extreme streamflow caused by increasing precipitation are anticipated in the future. The low flow shows much higher relative increments at the upstream of TP, which is mainly caused by changes in snow regulating (decreased snowfall and earlier snowmelt). However, those effects show weak influence on the streamflow in the downstream area, which would be more largely impact by the local precipitation change. In the future, irrigation, hydropower, and navigation in the TP could benefit from increased low flow in the TP, but the consistently increasing extreme high flow may indicate greater flood risk in the TP and downstream areas. Highlights • Hydrologic responses of both TP and the downstream area are evaluated. • Low streamflow would increase more significantly than high flow in TP. • Higher liquid precipitation and earlier snowmelt cause the increased low flow. • Change in snow regulating in TP has weak impact on downstream streamflow. [ABSTRACT FROM AUTHOR]

In order to explore the effects of the cascade bypass small hydropower stations (SHSs) on the water chemical characteristics and macroinvertebrate communities, three SHSs in Jingguhe stream of Lancang River basin have been investigated. A total of 50 species were recorded, including 4 mollusks, 5 Oligochaetas, and 41 aquatic insects, and the Polypedilum spp. was the dominant species. The results indicated that the construction and operation of SHSs had a significant impact on water velocity and depth but the water chemical characteristics. Some differences in Shannon–Wiener index and species richness were found between the dewatered reaches and the recovered-water reaches. Moreover, in these three SHSs, the density and biomass in recovered-water reaches were higher than in dewatered reaches. The relative abundances of filter collecters, predators, and scraper, as the different functional feeding groups, in mixed discharge sections were significantly higher than in reduced discharge sections for all SHSs. The macroinvertebrates community in dewatered reaches had been subjected to a certain external disturbances. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Southern Agriculture is the property of Journal of Southern Agriculture and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Vegetation plays a very important role of carbon (C) sinks in the global C cycle. With its complex terrain and diverse vegetation types, the Lancang River Basin (LRB) of southwest China has huge C storage capacity. Therefore, understanding the spatial variations and controlling mechanisms of vegetation C storage is important to understand the regional C cycle. In this study, data from a forest inventory and field plots were used to estimate and map vegetation C storage distribution in the LRB, to qualify the quantitative relationships between vegetation C density and altitude at sublot and township scale, and a linear model or polynomial model was used to identify the relationship between C density and altitude at two spatial scales and two statistical scales. The results showed that a total of 300.32 Tg C was stored in the LRB, an important C sink in China. The majority of C storage was contributed by forests, notably oaks. The vegetation C storage exhibited nonlinear variation with latitudinal gradients. Altitude had tremendous influences on spatial patterns of vegetation C storage of three geomorphological types in the LRB. C storage decreased with increasing altitude at both town and sublot scales in the flat river valley (FRV) region and the mid-low mountains gorge (MMG) region, and first increased then decreased in the alpine gorge (AG) region. This revealed that, in southwest China, altitude changes the latitudinal patterns of vegetation C storage; especially in the AG area, C density in the mid-altitude (3100 m) area was higher than that of adjacent areas. [ABSTRACT FROM AUTHOR]

In recent years, droughts and upstream/downstream water conflicts (such as those between water supply and demand) have been occurring frequently in the Lancang River basin, threatening local food security. In this research, the empirical orthogonal function (EOF) analysis and the rotated empirical orthogonal function (REOF) analysis were employed to investigate the temporal and spatial characteristics of precipitation variations during the crop growth period over 1960 to 2009. The results indicated the following: (1) annual precipitation increased slightly over the period of 1960–2009 but decreased significantly (at the 5% significance level) since 2001. An increasing trend was observed in the northern region, while a decreasing trend was observed in the southern region ; (2) five regions with different precipitation variation patterns were identified in the crop growth period, including the northern, the northeastern, the southwestern, the western, and the southernmost end patterns; (3) overall, a slightly increasing trend was identified in summer over the study period. Over the period of 2000–2009, precipitation in the summer and autumn decreased, (the strongest decreasing trend was observed in the autumn). Unlike that of the whole area, precipitation in the northern region decreased insignificantly in summer and increased slightly in autumn. Results of this study may facilitate the prevention of potential disasters (e.g., abnormal precipitation) and the reduction of the associated losses through early warning and forecasting of variation trends of regional precipitation. The approach could provide a support for decision-making related to international rivers and agricultural water resources management under global climate change. [ABSTRACT FROM AUTHOR]

Area weighting method was used to calculate average farmland natural quality in Lancang River basin in Yunnan Province, and statistical analysis techniques was used to analyze space distribution features of farmland natural quality inside the basin on the basis of farmland grading results of Yunnan Province. The results indicated that farmland natural quality zone scopes were divided into 1-26 grades, and every grade areas had great discrepancies, which showed a typical type skewness distribution and obvious space differences. Farmland natural quality zones presented a certain nonlinear correlation with soil type changes, latitude changes, and climate changes, etc. With the increase of latitude, decrease of climate heat and soil texture, the natural quality of farmland tends to decline. Discussing the space distribution features of farmland natural quality in Lancang River basin would optimize water allocation within the basin, provided scientific foundation for precisely mastering soil data, rationally utilize the land and formulate differentiated cultivated land quality promotion strategies. [ABSTRACT FROM AUTHOR]

Highlights: [•] A Lorenz curve is an effective way of assessing rainfall distribution. [•] Two indexes of Gini coefficient and Lorenz asymmetry coefficient from Lorenz Curve were defined. [•] A study of the rainfall concentration in the Lancang River has been carried out. [•] Significant trends were found in precipitation concentration index. [•] This work sheds new light on changing properties of rainfall in both time and space. [ABSTRACT FROM AUTHOR]

Based on the RUSLE model, this paper analyzed the ecosystem's soil conservation function and its spatial distribution in Lancang River Basin. This Basin could be one of the regions having the highest ecosystem's soil conservation capability in China, with an annual ecosystem's soil conservation amount being 2. 36×1010 t · a-1 and the soil conservation amount per unit area being 1453. 72 t · a-1 per hectare. The total amounts of the N, P, and K conserved in soils were 5. 74 × 107, 3. 07 ×107, and 3. 75 ×108 t · a-1, respectively, and presented an increasing trend from upstream to downstream. Among the ecosystems in the Basin, forest ecosystem had the highest soil conservation capability, followed by grassland and farmland, while desert ecosystem had the lowest one. The soil conservation capability of the ecosystems was linearly increased with the increase of vegetation coverage. Averagely, a 10% increment in the vegetation coverage could result in a 35.3% increment in soil conservation capability. To rationally increase the vegetation coverage by reliable ecosystem management based on local conditions would make good effect in preventing soil erosion and maintaining soil nutrients in the Basin. [ABSTRACT FROM AUTHOR]

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 (SPI1) and TMPA grid (SPI1), 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 SPI1, the consistency between SPI3 and SPI3 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, SPI3 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. [ABSTRACT FROM AUTHOR]

Based on the Lancang River Basin (LRB) hydro–meteorological data from 1961 to 2015, this study uses the Mann–Kendall trend test and mutation test to analyze the trend of hydro–meteorological variables, as well as which year the runoff series changes, respectively. We applied the Choudhury–Yang equation to calculate the climate and catchment landscape elasticity of runoff. Then we quantified the impact of climate change and human activities on runoff change. The results show that: (1) the mean annual precipitation (P) in LRB showed an insignificant decline, the annual potential evapotranspiration (E0) showed a significant increase, and the runoff depth (R) showed a significant decrease; (2) the abrupt change of the R occurred in 2005. Both the climate and catchment landscape elasticity of runoff increased, which means that the hydrological process of LRB became more sensitive to climate changes and human activities; (3) compared with the base period (1961–2004), the reduction of P was the leading cause of runoff reduction, with a contribution of 45.64%. The contribution of E0 and human activities to runoff changes are 13.91% and 40.45%, respectively. [ABSTRACT FROM AUTHOR]

Lancang River, the upstream reach of Mekong River, is a hotspot region in the sustainable management of water resources and environment as it is currently facing the deterioration of aquatic ecosystems. Nutrient balance (i.e., Phosphorus) in the Lancang-Mekong River Basin has become a highly disputed issue in recent years due to the construction of cascade hydropower stations. However, the estimation of the total phosphorus (TP) load faces great difficulties and challenges due to the absent measured water quality data. This study estimates the TP load based on the social economic data, analyzes the spatial distribution of TP and the contribution of different TP sources in the Lancang River basin under the level of social-economic development in 2014. Results show that the annual average TP load in the Lancang River Basin is 1.6 × 104–3.9 × 104 tons, which is at a very low level compared with other large-scale basins in China. The TP load from natural soil erosion dominates all other sources, accounting for 69%, followed by agricultural production and fertilization. In general, the TP load increases from upstream to downstream, but heterogeneity also exits in different regions under the influence of various factors, such as rainfall intensity, soil properties and human activities. The results reveal a holistic picture of TP load in the Lancang River Basin, which could provide a new perspective on the trans-border international river management. Unlabelled Image • The amount and spatial distribution of TP load in LRB is estimated. • Natural soil erosion is the main source of the TP load, accounting for 69%. • The spatial distribution of TP load is highly related with the intensity of rainfall. • TP load in LRB is at a low level compared with other large scale basins in China. [ABSTRACT FROM AUTHOR]

• Spatial-temporal distribution analysis identified vertical vegetation patterns. • Vertical correlations proved vegetation was more sensitive to temperature variation. • Predicted watershed vegetation response to RCP4.5 temperature scenario at pixel scale. • Identified potential risk of future vegetation adaption for river water quality. As the upper section of the Mekong River Basin, the vegetation quality of the Lancang River Basin (LRB) and the related ecological functions are critical for the whole basin. With time-series Moderate Resolution Imaging Spectroradiometer (MODIS) images from 2000 to 2015 and local daily climatic data since 1976, their vertical interaction differences were identified. The results showed that the spatial variation in Normalized difference vegetation index (NDVI) of grassland and forest were sensitive to elevation. The NDVI value in the southern area at elevations less than 3000 m was more than 0.80 and decreased to 0.30–0.60 with elevations higher than 4500 m. The general vegetation quality showed a positive trend under climate change over 16 years. The M-K test of daily precipitation and temperature from 12 local weather stations showed that the basin temperature varied more significantly than precipitation. The temporal correlation between NDVI with precipitation as well as temperature at each pixel indicated that temperature was the dominant factor affecting grassland and forest dynamics in the LRB. The interaction between vegetation and climate was more sensitive at elevations lower than 3000 m. Based on the RCP4.5 scenario, the future temperature distribution was predicted, and its impact on NDVI was simulated at the pixel scale. Under future drier and warmer climate conditions, the responded NDVI in the upper stream with higher elevation may increase soil erosion and decrease streamflow. The NDVI in the downstream area will be improved and be able to adapt to the related climate impacts. Because of the large amount of water and biomass in this basin, higher temperatures will accelerate the decomposition of forest foliar litter. Thus, more organic carbon and forest diffuse pollution will be discharged into the water, potentially affecting the water quality of the whole basin. [ABSTRACT FROM AUTHOR]

Benthic macroinvertebrate assemblages are one of the biological groups in aquatic ecosystem most sensitive to the habitat change and degradation, and can be a biological indicator for the aquatic ecosystem change and succession in cascading hydropower dam reservoir. The middle and lower reaches of the Lancang River are key spot for international biodiversity conservation and ecological studies on the effects of cascading hydropower dam exploitation. In this study, the reservoir of Manwan hydropower dam, the first dam in Lancang-Mekong river main stream, was selected as the study site. The benthic macroinvertebrate assemblages were sampled in 2011 and 2016 respectively. Meanwhile, the survey data before impounding (natural river, 1996) and early stage of single dam (1997) were collected to conduct the overall analysis for structure, distribution pattern and evolution of benthic macroinvertebrate assemblages. The results showed that the dominant biological group was gradually changed from the Oligochaeta and Insecta to the Mollusca. Along the longitudinal gradient, the density and biomass of the benthic macroinvertebrate assemblages were remarkably increased in reservoir, especially in the lacustrine zone. As for the functional feeding group, the predator and gatherer-collector changed into filter-collector predominantly in lacustrine zone. With the cascading dams operation, the biotic index indicated that the water quality of reservoir in 2016 was better than in 2011. The evolution of benthic macroinvertebrate assemblages in the Manwan Reservoir was related to the operation of Xiaowan dam in the upper reach, the hydrological regime and siltation in the reservoir, and would continue with dynamic changes with the operation of the cascading hydropower dam.