Source Region Of The Yangtze River Research Articles

Hydrologic Responses to Climate Change and Implications for Reservoirs in the Source Region of the Yangtze River

ABSTRACTUnderstanding the hydrological impacts of climate change is essential for robust and sustainable water management. This study assessed the hydrologic conditions under changing climate in the Jinshajiang River basin, the source region of the Yangtze River, using the hydrological model SWAT with the historical observations and the future climate simulations under two Shared Socioeconomic Pathways (SSP2‐4.5 and SSP5‐8.5). For the historical period, with an increasing trend of precipitation, evapotranspiration, and snowmelt, streamflow increases in upstream region but keeps decreasing in the downstream catchment. For future scenarios, a warmer and wetter climate is projected for the basin throughout the 21st century, leading to an overall increase in mean and extreme streamflow. The streamflow magnitude increases more significantly in the far future than in the near future, and more significant under SSP5‐8.5 than SSP2‐4.5. The projected remarkable increase in precipitation causes the transition in changing trend of streamflow compared with the historical period. The projected warming leads to a continuing decline in snowfall and snow water equivalent, followed by an earlier snowmelt and higher peak streamflow, especially at the upstream catchment. Ultimately, reservoirs in the basin are expected to gain more inflows, however, with greater variability including higher likelihoods of flood and drought events, which impose potential challenges on reservoir operations. These outcomes indicate the importance of adaptive water resources management in the melting water contributed basin to sustain and enhance its services under global warming.

Hydrological Modeling to Unravel the Spatiotemporal Heterogeneity and Attribution of Baseflow in the Yangtze River Source Area, China

Revealing the spatiotemporal variation in baseflow and its underlying mechanisms is critical for preserving the health and ecological functions of alpine rivers, but this has rarely been conducted in the source region of the Yangtze River (SRYR). Our study employed the Soil and Water Assessment Tool (SWAT) model coupled with two-parameter digital filtering and geostatistical approaches to obtain a visual representation of the spatiotemporal heterogeneity characteristics of the baseflow and baseflow index (BFI) in the SRYR. The SWAT model and multiple linear regression model (MLR) were used to quantitatively estimate the contribution of climate change and human activities to baseflow and BFI changes. The results underscore the robust applicability of the SWAT model within the SRYR. Temporally, the precipitation, temperature, and baseflow exhibited significant upward trends, and the baseflow and BFI showed contrasting intra-annual distribution patterns, which were unimodal and bimodal distribution, respectively. Spatially, the baseflow increased from northwest to southeast, and from the watershed perspective, the Tongtian River exhibited higher baseflow values compared to other regions of the SRYR. The baseflow and BFI values of the Dangqu River were greater than those of other tributaries. More than 50% of the entire basin had an annual BFI value greater than 0.7, which indicates that baseflow was the major contributor to runoff generation. Moreover, the contributions of climate change and human activities to baseflow variability were 122% and −22%, and to BFI variability, 60% and 40%. Specifically, precipitation contributed 116% and 60% to the baseflow and BFI variations, while the temperature exhibited contributions of 6% and 8%, respectively. Overall, it was concluded that the spatiotemporal distributions of baseflow and the BFI are controlled by various factors, and climate change is the main factor of baseflow variation. Our study offers valuable insights for the management and quantitative assessment of groundwater resources within the SRYR amidst climate change.

Geochemical baseline establishment and accumulation characteristics of soil heavy metals in Sabaochaqu watershed at the source of Yangtze River, Qinghai-Tibet Plateau

The establishment of soil geochemical baseline and heavy metal pollution assessment in the Qinghai-Tibet Plateau is of great significance for guiding environmental management in the high-cold and high-altitude regions. A total of 126 topsoil samples (0–20 cm) were collected and the contents of Cu, Pb, Zn, Ni, Cr, Cd, As and Hg were determined in the Sabaochaqu basin of the Tuotuo River, the source of the Yangtze River, in the Tibetan Plateau. The baseline values of 8 heavy metals were determined by mathematical statistics, iterative 2times standard deviation method, cumulative frequency and reference element standardization, and the soil heavy metal pollution in the study area was assessed by enrichment factor method and pollution index method. The results showed that the average contents of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn were 31.84, 0.29, 66.07, 17.35, 0.021, 27.86, 49.35 and 88.56 mg/kg, respectively. Baseline values were 22.24, 0.217, 64.16, 15.69, 0.0191, 26.46, 34.91, and 68.62 mg/kg, respectively. There is a great difference between the baseline value of soil heavy metals in study area and the Xizang soil background value, especially the baseline value of Cd was 2.68 times of its background value. The results of the pollution evaluation based on the baseline values showed that the 8 heavy metals were slightly enriched, and the overall pollution status was light pollution, and measures should be taken to control and manage them. The research results can provide a reference value for the evaluation of soil heavy metal pollution in the source region of the Yangtze River, and also provide a theoretical basis for the construction of soil heavy metal baseline values in similar high-cold and high-altitude regions.

Permafrost thaw and thermokarst in the source region of the Yangtze river in the central Tibetan plateau revealed by radar and optical remote sensing

AbstractThe landscape and landforms in permafrost regions are transforming due to climate change and permafrost thaw. This study uses optical and radar remote sensing, alongside spatial analysis, to examine thermokarst features and their driving factors in the source region of the Yangtze River (SRYR) on the central Tibetan Plateau. We analyse the distribution, interaction, and key environmental factors influencing thermokarst ponds and ground surface deformation, which are the two widespread and noticeable thermokarst features. Since the 1960s, the number of small water bodies has doubled from approximately ~2 × 104 to ~4 × 104 by the 2020s, with the median size of these water bodies decreasing from 2.3 × 104 m2 to 1.4 × 104 m2. The permafrost terrain has an average subsidence rate of 6.8 mm/a. About 50.9% of the SRYR exhibits evident thermokarst features. Surficial geological factors, especially geomorphology and slope, are primary factors in shaping the spatial distributions of thermokarst features. Both seasonal deformation and long‐term subsidence rates are more pronounced in areas with thermokarst ponds. However, once pond coverage exceeds around 5%, the amplifying effect on long‐term subsidence rates and seasonal deformation diminishes. The investigation further reveals that the relationship between seasonal deformation and long‐term subsidence is not strictly linear and that the combined increase in seasonal deformation and long‐term subsidence applies only to areas with seasonal deformation below approximately 20 mm. Beyond this threshold, the long‐term subsidence rate is no longer exacerbated by increased seasonal deformation.

Temporal and spatial evolution of net primary productivity in the Three-River Headwaters Region under phenological changes and anthropogenic influence.

Understanding the spatiotemporal changes in net primary productivity (NPP) and the driving factors behind these changes in climate-vulnerable regions is crucial for ecological conservation. This study simulates the actual NPP (NPPA) and climate potential NPP (NPPC) in the Three-River Headwaters Region from 2000 to 2020. The Theil-Sen Median method and Mann-Kendall mutation analyses are employed to explore their spatiotemporal variation patterns, while geographic weighted regression and machine learning are used to investigate the influence of anthropogenic activities and climatic factors on NPPA, the results indicate that the average NPPA across the entire region over multiple years is 382.506 , which is 0.132 times the average annual NPPC over the past 21years, showing an overall distribution pattern of low in the northwest and high in the southeast. The annual increase in NPPA from 2000 to 2020 is approximately 1.034 . The source region of the Yangtze River shows the largest improvement in vegetation, with 74.1% of the area showing improvement. Between 2002 and 2003, the annual NPPA in the Three-River Headwaters Region experienced a sudden change, lagging behind the NPPC change by 1year, and after 2005, the upward trend in NPPA became more pronounced. The impact of anthropogenic activities on NPPA shifted from positive to negative to positive from 2000 to 2020, with significant impact areas mainly concentrated in the northeast and a few areas in the central and southern parts. The proportion of areas with extremely significant impact increased from 1.9% in 2000 to 3.7% in 2020. Over the past 21years, the main factors influencing NPPA changes in the Three-River Headwaters Region have been soil moisture and precipitation, with the influence of different climate factors on NPP changing over time. Additionally, NPP is more sensitive to changes in altitude in low-altitude areas. This study can provide more accurate theoretical support for ecological environment assessment and subsequent protection efforts in the Three-River Headwaters Region.

Innovative trend analysis for the streamflow sub-time series of the source Region of the Yangtze River

Innovative trend analysis for the streamflow sub-time series of the source Region of the Yangtze River

Tree-Ring Inferred Drought Variations in the Source Region of the Yangtze, Yellow, and Mekong Rivers over the Past Five Centuries

The climate in the source region of the Yangtze River, Yellow River, and Mekong River is of great research interest because of its sensitivity to global change and its importance in regulating water resources to densely populated and vast areas downstream. A five-century long record of spring (May–June) for the Palmer Drought Severity Index (PDSI) was reconstructed for this region using tree-ring width chronologies of Qilian juniper (Juniperus przewalskii Kom.) from five high-elevation sites. The reconstruction explained 46% variance in the PDSI during the instrumental period 1955–2005. The reconstructed PDSI showed that the occurrence of dry extremes became frequent during the last century relative to the previous four centuries. The standard deviation of the reconstructed PDSI in the 100-year window showed that the recent century held apparent high values of standard deviation in the long-term context. Sustained droughts occurred in periods 1582–1631, 1737–1757, 1772–1791, 1869–1891, 1916–1939, and 1952–1982, whereas relatively wet intervals were observed in 1505–1527, 1543–1564, 1712–1736, 1792–1816, 1852–1868, 1892–1915, and 1983–2008. Notably, in the context of the past five centuries, the study region showed an increased inter-annual variability in the recent century, suggesting an intensified hydroclimatic activity possibly associated with global warming. Moreover, through diagnostic analysis of atmospheric circulation, we found that the negative phase East Asian–Pacific teleconnection pattern may be likely to trigger drought in the study region.

Does a braided river aggrade or degrade in response to changes in water and sediment fluxes?

Braided rivers undergo continuous morphological evolution in response to variations in water and sediment fluxes associated with a plethora of natural and anthropogenic disturbances, which has to date remained poorly understood. Here, a one-dimensional hydro-sediment-morphodynamic model is proposed for braided rivers. It is built upon an extended synthetic channel geometric model which encodes the essential, three-dimensional morphological information into a one-dimensional synthetic channel. It is first applied to the Rees River (New Zealand) to investigate overall morphological evolution (aggradation/degradation) during a single flood event. It is shown that the channel tends to degrade with increasing peak discharge and decreasing sediment supply, while the effect of baseflow discharge on aggradation/degradation is negligible unless the baseflow discharge exceeds a critical value. Then the proposed model is applied to resolve long-term morphological evolution in the Tuotuo River (China) reach (up to the year 2050), the source region of the Yangtze River, in response to projected water and sediment fluxes. Sustained degradation in the river reach is observed. The present study yields a viable physics-based method to predict overall aggradation or degradation of braided rivers under unsteady water and sediment fluxes over both short and long time scales.

Characteristics Analysis and Prediction of Land Use Evolution in the Source Region of the Yangtze River and Yellow River Based on Improved FLUS Model

Climate change profoundly alters land use in alpine regions, and delving into the evolutionary characteristics of these changes is crucial for the sustainable development of regional land resources and the gradual enhancement of the ecological environment. Taking the source region of the Yangtze and Yellow River (SRYAYE) as a case study, we integrate permafrost and snowfall data into the Future Land Use Simulation model (FLUS). Analyzing historical land use, we predict and simulate the land use scenarios for 2030, 2035, and 2060 under SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 climates, and conduct a detailed analysis of the scale, composition, and pattern of land use in this area. Scale. The results showed that ① the Kappa coefficient of the improved FLUS model was higher than 0.927, and that the overall accuracy of the simulation was increased by 2.64%; ② the area of forest land and the high-coverage grassland will increase in the future and the center of gravity will migrate to the west, and that the area of moderate and low-coverage grassland will slightly decrease but tend to become green to the west; and ③ the fragmentation degree of the SRYAYE is decreasing, and the influence of human activities on the landscape pattern is weaker than in the past.

Revealing temporal variation of baseflow and its underlying causes in the source region of the Yangtze River (China)

Abstract Baseflow plays a crucial role in sustaining the alpine ecosystem during rainless or cold periods. Despite its importance, information on how and why baseflow has changed in the source region of the Yangtze River (SRYR) is sparse. In our study, statistical analysis and the elastic coefficient method were used to identify the dynamic characteristics of baseflow and the underlying causes. The results show that monthly baseflow contributed 62–97% of runoff with a mean value of 75%, and they followed remarkable increasing trends from 1957 to 2020. The contributions of precipitation, temperature, evapotranspiration, and ecological conservation programs (ECPs) on baseflow variations were 86, 53, −15, and −24%, respectively. However, their contributions differed across months. During the warm months of May to September, precipitation played a dominant role, followed by evapotranspiration. In contrast, during other colder months, temperature was dominant; meanwhile, the effect of precipitation was almost absent. Moreover, climatic change had a hysteretic effect on baseflow variation, with a maximum lag time of 10 months. Our results highlighted critical roles of both precipitation and temperature, and indicated that climate change, rather than ECPs, dominated the variation in baseflow in the SRYR.

Response of Vegetation to Drought in the Source Region of the Yangtze and Yellow Rivers Based on Causal Analysis

The vegetation and ecosystem in the source region of the Yangtze River and the Yellow River (SRYY) are fragile. Affected by climate change, extreme droughts are frequent and permafrost degradation is serious in this area. It is very important to quantify the drought–vegetation interaction in this area under the influence of climate–permafrost coupling. In this study, based on the saturated vapor pressure deficit (VPD) and soil moisture (SM) that characterize atmospheric and soil drought, as well as the Normalized Differential Vegetation Index (NDVI) and solar-induced fluorescence (SIF) that characterize vegetation greenness and function, the evolution of regional vegetation productivity and drought were systematically identified. On this basis, the technical advantages of the causal discovery algorithm Peter–Clark Momentary Conditional Independence (PCMCI) were applied to distinguish the response of vegetation to VPD and SM. Furthermore, this study delves into the response mechanisms of NDVI and SIF to atmospheric and soil drought, considering different vegetation types and permafrost degradation areas. The findings indicated that low SM and high VPD were the limiting factors for vegetation growth. The positive and negative causal effects of VPD on NDVI accounted for 47.88% and 52.12% of the total area, respectively. Shrubs were the most sensitive to SM, and the response speed of grassland to SM was faster than that of forest land. The impact of SM on vegetation in the SRYY was stronger than that of VPD, and the effect in the frozen soil degradation area was more obvious. The average causal effects of NDVI and SIF on SM in the frozen soil degradation area were 0.21 and 0.41, respectively, which were twice as high as those in the whole area, and SM dominated NDVI (SIF) changes in 62.87% (76.60%) of the frozen soil degradation area. The research results can provide important scientific basis and theoretical support for the scientific assessment and adaptation of permafrost, vegetation, and climate change in the source area and provide reference for ecological protection in permafrost regions.

Quantification of Water Released by Thawing Permafrost in the Source Region of the Yangtze River on the Tibetan Plateau by InSAR Monitoring

AbstractThe source region of the Yangtze River (SRYR, 1.4 × 105 km2 above Zhimenda station) on the Tibetan Plateau (TP) has 78% permafrost coverage. The streamflow depth increased at a rate of 2.5 mm/a since 2000. Quantification of the water contribution brought by permafrost thawing is a difficult task. In this study, we used Sentinel‐1 data and the SBAS‐InSAR technique to monitor terrain deformation from September 2016 to December 2021, and then utilized the long‐term deformation rate to assess ground ice meltwater release and the seasonal deformation to evaluate water storage in the active layer. Results reveal that 55.3% of the terrain in the SRYR has subsidence >2.5 mm/a, indicating widespread ground ice melting. The release rate of ground ice meltwater is 4.3 mm/a in the entire SRYR, above 6 mm/a at the Dangqu and Tuotuo River subbasins. The water release rate is relatively small (∼3%) in comparison to the streamflow depth of 151 mm per year during the investigation period of 2017–2021. We did not detect a strong increasing or decreasing trend among the 5‐year seasonal deformation, which reflects that the total soil water content in the active layer did not change significantly during the short investigation period. The results provide a data basis for ground ice richness and loss information in the SRYR and help to understand the impact of permafrost thawing on the regional water cycle in the permafrost environment.

Characterizing precipitation uncertainties in a high-altitudinal permafrost watershed of the Tibetan plateau based on regional water balance and hydrological model simulations

Study regionthe source region of the Yangtze River (SRYR) Study focusPrecipitation uncertainties significantly impact water resource management, while the uncertainties of various precipitation products are not fully investigated due to the lack of observations, especially in high-altitudinal permafrost areas. In this study, we selected nine products representing three types of precipitation, including gauge-based, satellite-based and merged products, and conducted a comprehensive evaluation using regional water balance method and hydrological model simulations. New hydrological insights for the regionOur results indicate most precipitation products can replicate the observed precipitation decreasing trend with increasing elevation below 4500 m, but trends vary at higher elevations. The gauge-based precipitation products with bias correction outperform others, while most satellite-based products underestimate precipitation. The water-balance based evaluation shows a merged product (TPHiPr), and two gauge-based products perform best, followed by a satellite-based product (MSWEP). Process-based model simulations driven by selected precipitation products can reproduce daily runoff processes well in the entire SRYR (NSE = 0.68–0.86), but the performance degraded in the high-altitudinal Tuotuohe subbasin (NSE = 0.08–0.76). The runoff coefficients comparisons in these two regions also indicate the possible deficiencies of precipitation products in the high-altitudinal regions. Our results highlight the challenges of current precipitation products in characterizing the spatial and temporal precipitation changes in the high-altitudinal permafrost regions, and call for more accurate products in these areas.

Evaluation and Prediction of Water Quality of Typical Wetlands in the Source Region of the Yangtze River

Wetlands play an important role in water storage and water conservation, but with global climate change, the degradation of wetland ecosystems is accelerating. In this study, we conducted research on the current situation and future prediction of water quality in typical wetlands in the source region of the Yangtze River to provide a scientific basis for the protection and restoration of wetlands in the source region of the Yangtze River. The Bayesian water quality assessment method and Yao Zhiqi evaluation method were used to evaluate the water quality of typical wetlands in the source region of the Yangtze River from 2016 to 2021 and based on the climate change scenarios of three RCPs (Representative Concentration Pathways) under the CMIP5 (Coupled Model Intercomparison Project Phase 5) global climate model and SWAT (soil and water assessment tool) hydrological model, the wetland water quality in the source region of the Yangtze River from 2022 to 2100 was predicted. The results show that the inter-annual changes in CODMn, NH3-N, and TN in a typical wetland show a downward trend, while the temperature and DO concentration show an upward trend from 2016–2021. The changes in CODMn, temperature, and conductivity within the year are abundant season > flat season > dry season; and DO, NH3-A, TN, and TP concentrations within the year are opposite. The water quality of typical wetlands in the source region of the Yangtze River has reached Class II and above. From 2022 to 2100, under climate change in the future, TN, TP, CODMn, NH3-N, and temperature in the wetland water in the source region of the Yangtze River will continue to rise, and the concentration of DO will continue to decline. Therefore, the pressure on water resources in the source region of the Yangtze River is further aggravated, so it is urgent to strengthen water resources protection.

Hydrological response to climate change and human activities in the Three-River Source Region

Abstract. The Three-River Source Region (TRSR), which is known as “China's Water Tower” and affects the water resources security of 700 million people living downstream, has experienced significant hydrological changes in the past few decades. In this work, we used an extended variable infiltration capacity (VIC) land surface hydrologic model (VIC-Glacier) coupled with the degree-day factor algorithm to simulate the runoff change in the TRSR during 1984–2018. VIC-Glacier performed well in the TRSR, with Nash–Sutcliffe efficiency (NSE) above 0.68, but it was sensitive to the quality of the limited ground-based precipitation. This was especially marked in the source region of the Yangtze River: when we used Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks – Climate Data Record (PERSIANN-CDR), which has better spatial details, instead of ground-based precipitation, the NSE of Tuotuohe station increased from 0.31 to 0.86. Using the well-established VIC-Glacier model, we studied the contribution of each runoff component (rainfall, snowmelt, and glacier runoff) to the total runoff and the causes of changes in runoff. The results indicate that rainfall runoff contributed over 80 % of the total runoff, while snowmelt runoff and glacier runoff both contributed less than 10 % in 1984–2018. Climate change was the main reason for the increase in runoff in the TRSR after 2004, accounting for 75 %–89 %, except in the catchment monitored by Xialaxiu station. Among climate change factors, precipitation had the greatest impact on runoff. Finally, through a series of hypothetical climate change scenario experiments, we found that a future simultaneous increase in precipitation and temperature would increase the total runoff, rainfall runoff, and glacier runoff. The snowmelt runoff might remain unchanged because the increased precipitation, even with seasonal fluctuations, was basically completely compensated for by the decreased solid-to-liquid precipitation ratio. These findings improve our understanding of hydrological processes and provide insights for policy-makers on how to optimally allocate water resources and manage the TRSR in response to global climate change.

A dataset of boundaries data of the lakes (≥1.0 km2) in Qinghai Province in 2020

Located in the northeastern part of the Qinghai-Tibetan Plateau, Qinghai Province (31°39′–39°19′N, 89°35′–103°04′E) is the source region of the Yangtze River, the Yellow River and the Lantsang River. It is known as the China Water Tower. Contemporary survey of lakes in Qinghai Province is of great significance for understanding the impacts of climate change and promoting the ecological civilization construction. Based on Sentinel-2A/2B MSI images acquired in 2020, we first extracted the pixels of water body on account of the feature that the normalized difference water index (NDWI) greater than the normalized difference vegetation index (NDVI). Then we built the vector dataset of lake boundary with an area above 1.0 km2 in Qinghai Province after manual inspection and revision. Some attributes of the lake including its name, area, elevation, basin, administration and date were also attached. This dataset reflects the distribution of lakes in Qinghai Province in 2020, and can be used as a data source and scientific basis for researches on lake ecological protection, rational use of regional water resources, disaster prevention and mitigation in Qinghai Province.

Impacts of climate change and freeze–thaw cycles on water and sediment fluxes in the headwater region of the Yangtze River, Qinghai–Tibet Plateau

Variations in the suspended sediment on the Qinghai–Tibet Plateau have important implications for aquatic ecosystems. Although changes in the cryosphere induced by climate change have been shown to increase sediment yields, their impacts on water and sediment dynamics in headwater regions remain poorly investigated. Here, we examined the responses of runoff and suspended sediment dynamics to changes in the climate and ground freeze–thaw cycle in the source region of the Yangtze River (SRYR) from 1964 to 2019. Long–term daily in situ water and sediment observations provided evidence that climate change controlled change in seasonal and annual water–sediment dynamics by regulating air temperature and precipitation. Attribution analysis showed that precipitation (∼41.93 %, through driving rainfall splash, overland flow erosion, and mass wasting) and land surface temperature (∼30.66 %, through driving freeze–thaw erosion) were the major factors contributing to increasing fluvial sediment fluxes over the past 30 years. We found that freeze–thaw cycles changed the soil erosion patterns by governing the thermal state of the near–surface active layer and driving associated thermal processes. Furthermore, the extension of the thawing duration and the advance of the thawing starting date (at an average rate of 13.5 days/10 yr) exacerbated freeze–thaw erosion, leading to elevated sediment fluxes in the initial thaw and initial freezing periods. This study highlights the need to focus on cryosphere–hydrology observations in terms of sediment dynamics; these findings are critical for soil and ecological protection in alpine headwater regions.

Occurrence and Distribution of Long-Term Variability in Precipitation Classes in the Source Region of the Yangtze River

Various precipitation-related studies have been conducted on the Yangtze River. However, the topography and atmospheric circulation regime of the Source Region of the Yangtze River (SRYZ) differ from other basin parts. Along with natural uniqueness, precipitation constitutes over 60% of the direct discharge in the SRYZ, which depicts the decisive role of precipitation and a necessary study on the verge of climate change. The study evaluates the event distribution of long-term variability in precipitation classes in the SRYZ. The precipitation was classified into three precipitation classes: light precipitation (0–5 mm, 5–10 mm), moderate precipitation (10–15 mm, 15–20 mm, 20–25 mm), and heavy precipitation (>25 mm). The year 1998 was detected as a changing year using the Pettitt test in the precipitation time series; therefore, the time series was divided into three scenarios: Scenario-R (1961–2016), the pre-change point (Scenario-I; 1961–1998), and the post-change point (Scenario-II; 1999–2016). Observed annual precipitation amounts in the SRYZ during Scenario-R and Scenario-I significantly increased by 13.63 mm/decade and 48.8 mm/decade, respectively. The same increasing trend was evident in seasonal periods. On a daily scale, light precipitation (0–5 mm) covered most of the days during the entire period, with rainy days accounting for 83.50%, 84.5%, and 81.30%. These rainy days received up to 40%, 41%, and 38% of the annual precipitation during Scenario-R, Scenario-I, and Scenario-II, respectively. Consequently, these key findings of the study will be helpful in basin-scale water resources management.

Where does the runoff come from in dry season in the source region of the Yangtze River?

The present study focuses on the recharge source of the runoff of dry season based on the runoff change, stable isotopes and hydrochemical characteristics evidence in the source region of Yangtze River. The results showed that the runoff showed a significant increasing trend from 1956 to 2018 and the runoff increased by 21.5 m3/s·10a (Zhimenda station (ZMD)) and 40.0 m3/s·10a (Tuotuohe station (TTH)), especially in dry season. Moreover, the hydrogen and oxygen isotopes in dry season was more positive than that in wet season in the source region of Yangtze River. The main source of runoff in dry season is mainly affected by precipitation, supra-permafrost water and soil water in summer. Meanwhile, atmospheric precipitation, supra-permafrost water and soil water had a great impact on the recharge and the stable isotope characteristics of runoff of dry season. Furthermore, the hydrochemical type of runoff of dry season was similar as that for supra-permafrost water. Whether from the stable isotope or hydrochemical characteristics, it provides us with an idea that the main source of runoff of dry season is supra-permafrost water. Through the further analysis of recharge mode and recharge ratio of runoff of dry season, the major recharge sources of runoff of dry season is precipitation in autumn (TTH:58%, ZMD:61%). Moreover, the recharge patterns of runoff of dry season were direct recharge and indirect recharge. The subsequent findings could provide an overall understanding of the variational characteristics, causes, and sources of runoff of dry season and its hydrological effects in cold regions.

Spatial-temporal variations in vegetation and their responses to climatic and anthropogenic factors in upper reaches of the Yangtze River during 2000 to 2019

Environmental factors such as climate change and human activities are the basic driving forces that affect the growth and distribution of vegetation. Based on the MODIS-EVI data from 2000 to 2019, this paper analyzed the interannual changes of vegetation activity in the upper reaches of the Yangtze River (UYR), and examined their responses to climatic factors (effective precipitation, accumulative temperature and solar radiation) and anthropogenic factors (urbanization, afforestation). The results showed an increasing trend in EVI over the 20-year period, with an increasing rate of 0.021/10a. Contribution amount of effective precipitation, accumulative temperature, solar radiation and anthropogenic factors to EVI inter-annual variations in the UYR were 0.004/10a, 0.009/10a, 0.001/10a and 0.007/10a, respectively. Contribution rate of climate change and anthropogenic factors accounted for 67.8% and 32.2% of the total EVI changes respectively. In areas with significant changes in EVI, influence of anthropogenic factors is generally greater than that of climatic factors, especially in Chengdu-Chongqing urban agglomeration, Wujiang River Basin and the middle and lower reaches of the Jinsha River. In alpine regions such as the source region of the Yangtze River, significant changes in EVI were dominated by climatic factors.