Lancang River Basin Research Articles

Species composition, spatial distribution characteristics and topographic attribution of vegetation in the water-level-fluctuating zone of the Nuozhadu Reservoir in the Lancang River Basin

澜沧江最大梯级水库——糯扎渡水库运行之后，消落带许多原有植被物种被淹消亡，造成大面积次生裸地以及严重水土流失现象.消落带植被亟待生态修复，但缺乏基本数据支撑和参考.2020年7月，基于轻型无人机支持下的3S技术，结合现场调研，采用神经网络模型、空间叠加分析、景观格局指数以及典型相关性分析等方法，提取了糯扎渡水库典型消落带植被分类图及地形数据，定量分析了研究区本土物种组成、面积、覆盖率、分布特征、景观空间格局及地形解释.结果显示，研究区消落带植被覆盖率达74.13%，涵盖18种植物，物种数量仅占蓄水前的18.9%，原生植物仅剩飞机草（Chromolaena odorata）存活，物种组成趋于简单，以一年生草本和多年生草本为主，分别占比55.56%、33.33%，菊科占据优势，苍耳（Xanthium sibiricum）、狗牙根（Cynodon dactylon）、牛筋草（Eleusine indica）和藿香蓟（Ageratum conyzoides）为主要优势物种，分别占比47.41%、29.39%、9.37%和4.56%，可作为生态修复备选物种.地形因子对消落带植被影响大小：高程>地表起伏度>水体距离>坡度>地形湿度指数>坡向.研究区优势植物均呈聚集分布，消落带中下部、上部分别以苍耳和狗牙根斑块为主导，苍耳和狗牙根在斑块优势度、连通性以及形状复杂性方面均远大于牛筋草和藿香蓟，表现出了较强的生存潜力.苍耳在地表起伏度0~1.26 m区段覆盖良好，狗牙根、牛筋草在地表起伏度0.78~2.07 m区段覆盖良好，当地表起伏度>2.07 m，植被生长困难.植被景观格局的破碎化程度、斑块形状复杂性分别与地表起伏度呈正相关、负相关，即地表起伏度越大导致植被景观格局越破碎和斑块形状越简单，进而导致种群生存力减弱.;After the operation of the Nuozhadu Reservoir, the largest cascade reservoir along the Lancang River, the original vegetation in the water-level-fluctuating zone (WLFZ) was inundated and extinguished, resulting in large areas of secondary bare ground and severe soil erosion. Ecological restoration of vegetation in the WLFZ is necessary but lacking basic data support and scientific reference. In this paper, based on 3S technology supported by light drones and combined with field research, a neural network model, spatial superposition analysis, landscape pattern index and typical correlation analysis were used to extract the vegetation classification map and topographic data of the typical WLFZ of the Nuozadu Reservoir in July 2020, and to intuitively and quantitatively analyze the native species composition, area, coverage, distribution characteristics along the terrain, landscape spatial pattern and their topographic attribution in the study area. The results showed that the vegetation coverage of the study area reached 74.13%, covering 18 species of plants, with the number of species only 18.9% of that before the construction of the reservoir. Only Chromolaena odorata (Chr) survived in the native plants. The species composition tended to be simple, with annual and perennial herbs dominating, accounting for 55.56% and 33.33% respectively, with Asteraceae as the dominant family, Xanthium sibiricum (Xan), Cynodon dactylon (Cyn), Eleusine indica (Ele) and Ageratum conyzoides (Age) were the dominant species, accounting for 47.41%, 29.39%, 9.37% and 4.56% respectively, and could be used as alternative species for restoration. The vegetation in the WLFZ was affected by topographic factors in the following order:elevation>surface fluctuation>nearest water distance>slope>topographic humidity index>slope direction. The dominant plants in the study area were all aggregated distributed, with patches of Xan and Cyn dominating the lower-middle part and upper part of the WLFZ respectively, with Xan and Cyn showing much greater patch dominance, connectivity and shape complexity than Ele and Age, showing a stronger potential for survival. Xan was well covered in the 0-1.26 m section of surface fluctuation, and Cyn and Ele were well covered in the 0.78-2.07 m section of surface fluctuation. When the surface fluctuation was >2.07 m, the vegetation growth was difficult. The degree of fragmentation of the vegetation landscape pattern and the complexity of the patch shape were positively and negatively correlated with the surface fluctuation respectively, i.e. the greater the surface fluctuation led to the more fragmented and simple shape of the vegetation landscape pattern, which in turn led to a reduction in the viability of the population.

Multiple Effects of Topographic Factors on Spatio-Temporal Variations of Vegetation Patterns in the Three Parallel Rivers Region, Southeast Qinghai-Tibet Plateau

Topographic factors are critical for influencing vegetation distribution patterns, and studying the interactions between them can enhance our understanding of future vegetation dynamics. We used the Moderate-resolution Imaging Spectroradiometer Normalized Differential Vegetation Index (MODIS NDVI) image dataset (2000–2019), combined with the Digital Elevation Model (DEM), and vegetation type data for trend analysis, and explored NDVI variation and its relationship with topographic factors through an integrated geographically-weighted model in the Three Parallel Rivers Region (TPRR) of southeastern Qinghai-Tibet Plateau (QTP) in the past 20 years. Our results indicated that there was no significant increase of NDVI in the entire basin between 2000–2019, except for the Lancang River basin. In the year 2004, abrupt changes in NDVI were observed across the entire basin and each sub-basin. During 2000–2019, the mean NDVI value of the whole basin increased initially and then decreased with the increasing elevation. However, it changed marginally with variations in slope and aspect. We observed a distinct spatial heterogeneity in vegetation patterns with elevation, with higher NDVI in the southern regions NDVI than those in the north as a whole. Most of the vegetation cover was concentrated in the slope range of 8~35°, with no significant difference in distribution except flat land. Furthermore, from 2000 to 2019, the vegetation cover in the TPRR showed an improving trend with the changes of various topographic factors, with the largest improvement area (36.10%) in the slightly improved category. The improved region was mainly distributed in the source area of the Jinsha River basin and the southern part of the whole basin. Geographically weighted regression (GWR) analysis showed that elevation was negatively correlated with NDVI trends in most areas, especially in the middle reaches of Nujiang River basin and Jinsha River basin, where the influence of slope and aspect on NDVI change was considerably much smaller than elevation. Our results confirmed the importance of topographic factors on vegetation growth processes and have implications for understanding the sustainable development of mountain ecosystems.

Evaluations of Remote Sensing-Based Global Evapotranspiration Datasets at Catchment Scale in Mountain Regions

Evapotranspiration (ET) is essential for connecting ecosystems and directly affects the water consumption of forests, grasslands, and farmlands. Eight global remote sensing-based ET (RS_ET) datasets generated using satellite imagery and ground-based observations were comprehensively assessed using monthly ET time series simulated by the water balance (WB) method at the catchment scale in the Hengduan Mountain (HDM) region, including the Nu River, Lancang River, and Jinsha River basins. The complementary relationship (CR) model, which derives ET from meteorological data, was also evaluated against WB-based ET (WB_ET). In addition, WB_ET, RS_ET, and CR-based ET (CR_ET) data were used to investigate ET spatial and temporal variations at the catchment, grid, and site scale, respectively. Most RS_ET datasets accurately simulated monthly ET with an average index of agreement ranging from 0.71–0.91. The Operational Simplified Surface Energy Balance dataset outperformed other RS_ET datasets, with Nash–Sutcliffe efficiency coefficient (NSE) and Kling–Gupta efficiency values of 0.80 and 0.90, respectively. RS_ET datasets generally performed better in northern semiarid areas than in humid southern areas. The monthly ET simulation by the CR model was consistent with that of the WB_ET in the HDM region, with mean values of correlation coefficient (cc) and NSE at each site of 0.89 and 0.68, respectively. The model showed better performance in simulating monthly ET in the Lancang River Basin than in the Nu River and Lancang River basins, with mean cc and NSE of 0.92 and 0.83, respectively. Generally, annual ET trends were consistent at the catchment, grid, and site scale, as estimated by the WB method, RS_ET datasets, and CR model. It showed a significant decreasing trend in the northern semiarid region of the HDM while exhibiting an increasing trend in the humid southern region.

Extreme precipitation variability across the Lancang‐Mekong River Basin during 1952–2015 in relation to teleconnections and summer monsoons

AbstractThe Lancang‐Mekong River Basin (LMRB) is home to ~70 million people whose life and livelihood are mostly dependent upon precipitation as the primary freshwater source. Hence, identifying potential oceanic–atmospheric drivers of regional precipitation variability is becoming increasingly important for the sustainable development of the LMRB. This study first investigated spatio‐temporal variability and trends in extreme precipitation characteristics (in terms of intensity, frequency, and duration) throughout the LMRB during 1952–2015, using gauge‐based gridded daily precipitation time series. Then, the associations between the historical extreme precipitation characteristics and seven teleconnection and five summer monsoon indices were explored. On the basin scale, no statistically significant (p < .05) trends were detected in annual extreme precipitation intensity, frequency, and duration indices. The number of wet days (R1mm) significantly increased in both the Mekong River Basin (MRB) and the Lancang River Basin (LRB), predominantly leading to longer wet spells in these two sub‐basins. Spatially, the relatively high extreme precipitation intensity and frequency indices, as well as consecutive wet days (CWD), significantly increased in the south, east, and northwest of MRB, while decreased in the west of MRB and the north of LRB. The intensity and frequency of historical extreme precipitations over the LMRB were most significantly correlated with the East Asian Summer Monsoon Index, North Atlantic Oscillation, and East Pacific/North Pacific pattern. However, the wet/dry spells showed the strongest associations with the Atlantic Multi‐decadal Oscillation/the Southern Oscillation Index on the interannual/decadal time scales (3–4/8–15 years) during 1986–1999/1968–2002, respectively.

Effects of climate change on terrestrial water storage and basin discharge in the lancang River Basin

Study RegionLancang River Basin (upper reaches of the Mekong River basin within China). Study FocusComplex 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 RegionThe 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.

Length–weight relationship of six endemic fish species in the Qinghai‐Tibet Plateau, China

Length–weight relationships of six endemic fish species collected from the Qinghai-Tibet Plateau (including the Yarlung Zangbo River basin, the Lancang River basin, and the Nujiang River basin) were analyzed in this study. All fish specimens were landed seasonally during 2017 (rainfall season: June to July, rainless season: August) to 2018 (rainfall season: March to June, rainless season: August to October). Stationary gillnets (mesh size: 3, 5, and 8 cm, 20 m × 1.5 m) and lobster pot (10 m long, mesh size: 1 cm) were applied for fish specimens capture. Each individual was measured immediately after capture with the precision of 0.1 cm for total length (TL) and 0.1 g for body weight (BW), respectively. Strong correlation between length-weight of all the six species were detected (r2 > 0.96). The estimate range of parameter a was form 0.0036 to 0.0129. The exponent b ranged from 2.7923 to 3.2409, which is consistent with expected interval (2.5–3.5). New maximum total length were recorded for the species of Schizothorax nukiangensis and Triplophysa stolickai, respectively.

Spatiotemporal analysis of water resources system vulnerability in the Lancang River Basin, China

The Lancang River (Upper Mekong), originated from Qinghai-Tibet Plateau, is the main water source for Southeast Asia countries. In recent years, people have paid more and more attention to the impact of climate change and human activities on the Lancang River water resources system. Due to external disturbances, the vulnerability of water resources in the Lancang River Basin (LRB) is also changing, leading to an increase in the probability of possible risks. This study proposes an assessment framework to evaluate water resources system vulnerability and analyze its dynamic change in the LRB during 1998–2014. Quantitative approaches for calculation of sensitivity, exposure, hazard and adaptability are respectively formulated, which highlight the impacts of natural and anthropogenic interference on water resources. Specific management strategies are put forward based on the spatial recognition of water resources system vulnerable areas in the LRB. The results indicate that the sensitivity and exposure of the LRB show an upward trend, while the adaptive capacity shows a downward trend during 1998–2014. The vulnerability of the LRB is at low level currently. However, fluctuations in its vulnerability have increased over time. As a whole, the vulnerability displays a high-to-low gradient from southeast to northwest of the LRB during the study period, the Dali region is the most vulnerable region in the LRB. The areas with high vulnerability are distributed in the southeast of the study area, mainly in the mainstream areas with characterization of frequent human interferences, tend to increase persistently. Based on the results, some suggestions targeted at different vulnerable areas were proposed. This study maps the spatiotemporal characteristics of the water resource vulnerability in the LRB, which reveals hotspot areas from climate-related threats and can provide useful information to improve the adaptation and resilience of the water resources system.

Dynamics and Drivers of Vegetation Phenology in Three-River Headwaters Region Based on the Google Earth Engine

Phenology shifts over time are known as the canary in the mine when studying the response of terrestrial ecosystems to climate change. Plant phenology is a key factor controlling the productivity of terrestrial vegetation under climate change. Over the past several decades, the vegetation in the three-river headwaters region (TRHR) has been reported to have changed greatly owing to the warming climate and human activities. However, uncertainties related to the potential mechanism and influence of climatic and soil factors on the plant phenology of the TRHR are poorly understood. In this study, we used harmonic analysis of time series and the relative and absolute change rate on Google Earth Engine to calculate the start (SOS), end (EOS), and length (LOS) of the growing season based on MOD09A1 datasets; the results were verified by the observational data from phenological stations. Then, the spatiotemporal patterns of plant phenology for different types of terrain and basins were explored. Finally, the potential mechanism involved in the influence of climatic and soil factors on the phenology of plants in the TRHR were explored based on the structural equation model and Pearson’s correlation coefficients. The results show the remotely sensed monitoring data of SOS (R2 = 0.84, p < 0.01), EOS (R2 = 0.72, p < 0.01), and LOS (R2 = 0.86, p < 0.01) were very similar to the observational data from phenological stations. The SOS and LOS of plants possessed significant trends toward becoming advanced (Slope < 0) and extended (Slope > 0), respectively, from 2001 to 2018. The SOS was the earliest and the LOS was the longest in the Lancang River Basin, while the EOS was the latest in the Yangtze River Basin owing to the impact of climate change and soil factors. Meanwhile, the spatial patterns of SOS, EOS, and LOS have strong spatial heterogeneity at different elevations, slopes, and aspects. In addition, the results show that the drivers of plant phenology have basin-wide and stage differences. Specifically, the influence of soil factors on plant phenology in the Yangtze River Basin was greater than that of climatic factors, but climatic factors were key functional indicators of LOS in the Yellow and Lancang river basins, which directly or indirectly affect plant LOS through soil factors. This study will be helpful for understanding the relationship between the plant phenology of the alpine wetland ecosystem and climate change and improving the level of environmental management.

Assessment of GPM IMERG Satellite Precipitation Estimation under Complex Climatic and Topographic Conditions

Satellite precipitation estimation provides crucial information for those places lacking rainfall observations from ground–based sensors, especially in terrestrial or marine areas with complex climatic or topographic conditions. This is the case over much of Western China, including Upper and Middle Lancang River Basin (UMLRB), an extremely important transnational river system in Asia (the Lancang–Mekong River Basin) with complex climate and topography that has limited long–term precipitation records and high–elevation data, and no operational weather radars. In this study, we evaluated three GPM IMERG satellite precipitation estimation (IMERG E, IMERG L and IMERG F) over UMLRB in terms of multi–year average precipitation distribution, amplitude consistency, occurrence consistency, and elevation–dependence in both dry and wet seasons. Results demonstrated that monsoon and solid precipitation mainly affected amplitude consistency of precipitation, aerosol affected occurrence consistency of precipitation, and topography and wind–induced errors affected elevation dependence. The amplitude and occurrence consistency of precipitation were best in wet seasons in the Climate Transition Zone and worst in dry seasons in the same zone. Regardless of the elevation–dependence of amplitude or occurrence in dry and wet seasons, the dry season in the Alpine Canyon Area was most positively dependent and most significant. More significant elevation–dependence was correlated with worse IMERG performance. The Local Weighted Regression (LOWERG) model showed a nonlinear relationship between precipitation and elevation in both seasons. The amplitude consistency and occurrence consistency of both seasons worsened with increasing precipitation intensity and was worst for extreme precipitation cases. IMERG F had great potential for application to hydroclimatic research and water resources assessment in the study area. Further research should assess how the dependence of IMERG’s spatial performance on climate and topography could guide improvements in global precipitation assessment algorithms and the study of mountain landslides, floods, and other natural disasters during the monsoon period.

An improved modeling of precipitation phase and snow in the Lancang River Basin in Southwest China

An improved modeling of precipitation phase and snow in the Lancang River Basin in Southwest China

Relationships between stoichiometric characteristics of soil enzymatic activities and environmental factors in parallel valleys of western Yunnan, China.

The valleyes of Hengduan Mountains contain the landscapes with high heterogeneity as well as high diversity of climate and vegetation types. To explore the soil cycling of four elements (C, N, P, S) across the parallel valleys of Nujiang River, Lancang River, Jinsha River and Yuanjiang River in western Yunnan, we collected top soils (0-10 cm) in forests, grasslands, and croplands. The activities of soil enzymes, including β-glucosidase (BG), β-N-acetylglucosaminidase (NAG), acid phosphatase (AP), and sulfatase (SU), which drive the soil C, N, P and S cycling, were determined. We analyzed the relationships of soil enzymatic activities and their stoichiometric characteristics with environmental factors. The activities of both AP and NAG had significant difference among different basins and different land types. The activities of AP, BG, NAG and SU were significantly positively related with each other. From southeast to northwest, the activities of BG, NAG, and SU increased with the altitude. Across all basins, the ecoenzymatic ratios of soils always ranked as AP:SU > BG:SU > NAG:SU > BG:NAG > BG:AP > NAG:AP. Compared with forest and grassland soil, cropland soils in each watershed had a higher BG:NAG and a lower NAG:AP (except Yuanjiang River basin). Moreover, AP:SU, BG:SU and NAG:SU of cropland soils were lower than those of forest and grassland in Yuanjiang River basin. However, they were higher than forest and lower than grassland in both Lancang River basin and Jinsha River basin. Soil enzyme activities and enzymatic stoichiometry were affected by physicochemical properties of soil, climate, and location, with the most contribution from soil physicochemical properties. Agricultural land use significantly affected the stoichiometry of C:N:P acquiring enzymes in soils by reducing the activity of N-degrading enzymes relative, resulting in the increases of BG:NAG and the decreases of NAG:AP. Agricultural activities had limited effects on other enzymatic stoichiometries.

An efficient and accurate Mixed‐integer linear programming model for long‐term operations of large‐scale hydropower systems

Mixed-integer linear programming is widely used in hydropower reservoirs operation optimisation because of its modelling flexibility, solution stability, and global search capability. A major obstacle to applying mixed-integer linear programming to hydropower reservoirs operation optimisation, especially for long-term operations of large-scale hydropower systems, is the non-linear phenomenon while converting water energy into electricity, which is normally expressed as a non-linear bivariate function, that is, hydropower production function. To cross this technological barrier, a novel linearisation method for hydropower production function is proposed. The method uses rectangular meshing techniques to approximate hydropower production function. Then Special Ordered Sets of type 2 (SOS2)constraints are adopted for sub-rectangle selection, which are formulated based on the binary branching schemes generated by binary reflected grey code. The proposed method can linearise the hydropower production function with only logarithmic-sized binary variables of the traditional methods and maintain high accuracy. The method is then applied to optimising the operation of the Lancang River Basin hydropower system, which has 13 head-dependent reservoirs with a deterministic model and a two-stage stochastic model. The results show that the authors' method significantly outperforms conventional linearisation methods and can obtain accurate solutions within an acceptable time for deterministic and stochastic large-scale hydropower reservoirs operation optimisation problems.

Uncertainty Analysis of SWAT Modeling in the Lancang River Basin Using Four Different Algorithms

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.

Quantifying the Impacts of Climate Change and Human Activities on Runoff in the Lancang River Basin Based on the Budyko Hypothesis

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.

Do model parameters change under changing climate and land use in the upstream of the Lancang River Basin, China?

ABSTRACT Hydrological model parameters may vary under the impacts of climate and land-use change. This study proposes a hydrological modelling framework based on the Soil and Water Assessment Tool (SWAT) to investigate the variability of model parameters in three different experiments and to assess the impacts of climate and/or land-use change on these parameters in the upstream of the Lancang River Basin, China. In Experiment 1 (E1), most parameters show clear temporal trends under changing climate and land use, implying that model parameters are strongly influenced by their combined effects. Experiments 2 (E2) and 3 (E3) investigate the separate impacts of land-use change and climate change, respectively. Due to the almost invisible changes in land use in E2, there is no change detected in the model parameters. Temporal trends are found in most parameters in E3 and over half of them show consistent trends with E1, which indicates that climate change has greater impacts on model parameter variability. The simulated extreme streamflow and sediment fluxes vary substantially with time-variant parameters, implying that the variations in model parameters do matter for hydrological prediction.

The transborder flux of phosphorus in the Lancang-Mekong River Basin: Magnitude, patterns and impacts from the cascade hydropower dams in China

Nutrients are critical to the development of plant and animal life in the river ecological system. In recent years, more attentions have arisen on the impact of building hydropower dams to transborder nutrient flux in the Lancang-Mekong River Basin (LMRB). In this paper, phosphorus was taken as an example, which is considered as one of the most significant factors to limit biological activities in the river. The Soil and Water Assessment Tool (SWAT) was used to access the multisource loading pattern of Total Phosphorus (TP) under no-dam scenario, and various types of dam construction scenarios analyses were performed to investigate potential changes in the transborder TP flux from Lancang River Basin (LRB, Chinese part of LMRB) to lower LMRB (other parts of LMRB). The results showed that the Total Phosphorus load in the LRB is about 27,079 tons/year, of which 85% TP is collected from July to October. The annual TP export at the outlet of the LRB is 14,112 tons/year under no-dam scenario, which accounts for about 4.2% of the total TP loads in the lower LMRB. With seven to twenty-one dams included in experiments, TP flux at the outlet of the LRB decreased 50–59%, while the delivered ratio for the lower LMRB decreased 2.1–2.5%. As a summary, building dams has a significant impact on the TP transport pattern in the Chinese part of LMRB, but very limited effect in lower LMRB according to the modeling results, especially for the Mekong delta. Moreover, the existing dams (seven dams) seem to intercept much more phosphorus than those dams that are under construction.

Comprehensive Study on Freshwater Ecosystem Health of Lancang River Basin in Xishuangbanna of China

The Lancang-Mekong River significantly affects the livelihood of residents in the basin as well as the lives of people in other regions of the world in terms of great development potential and its economic and ecological values. In the meanwhile, the river attracts the attention of countries in the basin and the international community because it raises potential for international conflicts. The Lancang-Mekong River leaves China from Xishuangbanna and the ecosystem status in Xishuangbanna constitutes one of the top concerns related to the basin. The study comprehensively evaluates the status of freshwater ecosystem health of the Lancang River in Xishuangbanna for the first time, with reference to aspects of ecosystem vitality, ecosystem services, as well as governance and stakeholders, firstly, linking the ecosystem and the benefits it provides as well as human activities as an organic whole. The methodology used, Freshwater Health Index, is newly developed and constitutes revision of the first attempt of its usage. Basically, the freshwater ecosystem in the studied area and period remains healthy according to the research, and the ecosystem is considered to be capable of providing sufficient services and benefits to meet the economic and societal development demands. Recommendations are proposed for more sustainable local freshwater management and utilization accordingly.

Influence of climatic factors on the potential distribution of pest Heortia vitessoides Moore in China

Heortia vitessoides Moore is one of the predominant pests of Aquilaria sinensis (Lour.) Spreng, which is extremely harmful to this plant, and is also an important quarantine pest around the world. To understand the influence of climate factors on the distribution of this pest, maximum entropy modeling (MaxEnt) was used to predict the potential suitable distribution area under certain climatic conditions. The results showed that H. vitessoides was mainly located in the tropical and southern subtropical climate areas of China under current climatic conditions, with a total suitable distribution area of 107.48 × 104 km2. The highly suitable areas were concentrated in the Pearl River Basin and the south of Lancang River Basin with area of 46.19 × 104 km2. In the future, the suitable area showed a tendency to expand to the north. The total suitable distribution area of this species would reach 136.21 × 104-151.62 × 104 km2, which was 26.62%–40.65% higher than that of the current. The climatic factors of precipitation of warmest quarter, precipitation of wettest quarter, min temperature of coldest month, and mean temperature of warmest quarter were the dominant variables affecting the distribution of H. vitessoides. It can be seen that the suitable area of this pest is relatively large and tends to expand, which poses a threat to the growth of A. sinensis. It is suggested that the relevant afforestation and phytosanitary departments should attach great importance and take necessary measures to control the spread of this pest.

Spatial characteristics of total phosphorus loads from different sources in the Lancang River Basin

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.

Evaluation of Water Yield and Soil Erosion in the Three-River-Source Region under Different Land-Climate Scenarios

Exploring the water yield and soil conservation in the Three-River-Source region is of great significance for evaluating both the ecological stability of the Qinghai-Tibet Plateau, Yellow River basin, Yangtze River basin and Lancang River basin and the sustainable development of human society. The data sources for this study were land use/cover data from four phases (2000, 2005, 2010 and 2015), daily precipitation and temperature datasets, and the 1:1000000 Chinese soil database. These data were combined with vector data, such as data on settlements, roads, and rivers, along with population, economic raster datasets and CCSM4 common climate model prediction results. The Three-River-Source region was taken as the study area, and four land use/cover development scenarios and two climate change scenarios were designed based on the FLUS model and the downscaling correction method. The InVEST model was used to quantitatively simulate the water yield and soil erosion under different scenarios in the study area in 2030. The results showed the following: (1) Under different land use/cover development scenarios, grassland remained the dominant land use/cover type in the Three-River-Source region, and the area ratio was always greater than 67%. (2) Under the RCP4.5 climate scenario, the annual water yield and soil erosion increased by more than 7% and 3.9%, respectively. Under the RCP8.5 climate scenario, the annual water yield and soil erosion decreased by more than 3.3% and 1.3%, respectively. (3) Climate change played a leading role in the changes in water yield and soil erosion. Climate change contributed as much as 89.97%–98.00% to the change in water yield and 60.49%–95.64% to the change in the soil erosion modulus. However, the contribution of land use/cover changes to the change in regional water yield was only 2.00%–10.03%, and the contribution of the soil erosion modulus change was 4.36%–39.91%. Therefore, the land use development strategy in the Three-River-Source region should comprehensively consider issues such as regional development, the input of returning farmland to forest and grassland, and the resulting ecological benefits.