Climate change has led to increased frequency, duration, and severity of meteorological drought (MD) events worldwide, causing significant and irreversible damage to terrestrial ecosystems. Understanding the impact of MD on diverse vegetation types is essential for ecological security and restoration. This study investigated vegetation responses to MD through a drought propagation framework, focusing on the Yangtze River Basin in China, which has been stricken by drought frequently in recent decades. By analyzing propagation characteristics, we assessed the sensitivity and vulnerability of different vegetation types to drought. Using Copula modeling, the occurrence probability of vegetation loss (VL) under varying MD conditions was estimated. Key findings include: (1) The majority of the Yangtze River Basin showed a high rate of MD to VL propagation. (2) Different vegetation types exhibited varied responses: woodlands had relatively low sensitivity and vulnerability, grasslands showed medium sensitivity with high vulnerability, while croplands demonstrated high sensitivity and moderate vulnerability. (3) The risk of extreme VL increased sharply with rising MD intensity. This framework and its findings could provide valuable insights for understanding vegetation responses to drought and inform strategies for managing vegetation loss.

Introduction The particle size characteristics of irregular sediments in the Yangtze River Source Area (YRSA) are pivotal for understanding the mechanical properties of the sedimentary medium.Methods This study utilizes field sediment sampling, laser scanning, laboratory testing, and mathematical statistics to analyze the morphological, geometric, mineralogical, and accumulation characteristics of sediment particles in the region.Results Our findings indicate that sediments in the YRSA have angular edges and deviate from spherical shapes, exhibiting elongated and flatter three-dimensional morphologies. In the experiment, the sliding plate method was used to measure the angle of repose of the sediments, which was found to be 36.7 degrees above water and 35.9 degrees below water. Both values are higher than the typical range for non-plateau regions, indicating reduced sediment mobility. The sediments are composed of fine-grained and coarse-grained soils. The particle size distribution is primarily coarse sand (0.5-2.0 mm), fine gravel (2.0-5.0 mm), and medium gravel (5.0-20.0 mm), with a significant coarsening trend observed over the past six years. The mineral composition, dominated by quartz, feldspar, and heavy minerals, is stable, with approximately 70% of the minerals having a hardness of >= 7 on the Mohs scale. The most abundant trace elements are Ti, Mn, Ba, P, Sr, Zr, and Cl.Discussion This research reveals that the sediment characteristics in the YRSA are markedly different from those of natural sands in non-plateau regions, necessitating a reevaluation of conventional theories and engineering practices for engineering constructions in this area. The insights from this study are profound and practically relevant, illuminating the sediment transport dynamics in alpine river systems and supporting sustainable regional development.

Study region: The source area of the Yangtze River, a typical catchment in the cryosphere on the Tibet Plateau, was used to develop and validate a distributed hydrothermal coupling model. Study focus: Climate change has caused significant changes in hydrological processes in the cryosphere, and related research has become hot topic. The source area of the Yangtze River (SAYR) is a key catchment for studies of hydrological processes in the cryosphere, which contains widespread glacier, snow, and permafrost. However, the current hydrological modeling of the SAYR rarely depicts the process of glacier/snow and permafrost runoff from the perspective of coupled water and heat transfer, resulting in distortion of simulations of hydrological processes. Therefore, we developed a distributed hydrothermal coupling model, namely WEP-SAYR, based on the WEP-L (Water and energy transfer process in large river basins) model by introducing modules for glacier and snow melt and permafrost freezing and thawing. New hydrological insights for the region: In the WEP-SAYR model, the soil hydrothermal transfer equations were improved, and a freezing point equation for permafrost was introduced. In addition, the glacier and snow meltwater processes were described using the temperature index model. Compared to previously applied models, the WEP-SAYR portrays in more detail glacier/ snow melting, dynamic changes in permafrost water and heat coupling, and runoff dynamics, with physically meaningful and easily accessible model parameters. The model can describe the soil temperature and moisture changes in soil layers at different depths from 0 to 140 cm. Moreover, the model has a good accuracy in simulating the daily/monthly runoff and evaporation. The Nash-Sutcliffe efficiency exceeded 0.75, and the relative error was controlled within +/- 20 %. The results showed that the WEP-SAYR model balances the efficiency of hydrological simulation in large scale catchments and the accurate portrayal of the cryosphere elements, which provides a reference for hydrological analysis of other catchments in the cryosphere.

There is 78 % permafrost and seasonal frozen soil in the Yangtze River's Source Region (SRYR), which is situated in the middle of the Qinghai-Xizang Plateau. Three distinct scenarios were developed in the Soil and Water Assessment Tool (SWAT) to model the effects of land cover change (LCC) on various water balance components. Discharge and percolation of groundwater have decreased by mid-December. This demonstrates the seasonal contributions of subsurface water, which diminish when soil freezes. During winter, when surface water inputs are low, groundwater storage becomes even more critical to ensure water supply due to this periodic trend. An impermeable layer underneath the active layer thickness decreases GWQ and PERC in LCC + permafrost scenario. The water transport and storage phase reached a critical point in August when precipitation, permafrost thawing, and snowmelt caused LATQ to surge. To prevent waterlogging and save water for dry periods, it is necessary to control this peak flow phase. Hydrological processes, permafrost dynamics, and land cover changes in the SRYR are difficult, according to the data. These interactions enhance water circulation throughout the year, recharge of groundwater supplies, surface runoff, and lateral flow. For the region's water resource management to be effective in sustaining ecohydrology, ensuring appropriate water storage, and alleviating freshwater scarcity, these dynamics must be considered.

Study region: The source region of the Yangtze River in the Qinghai-Tibet Plateau, China. Study focus: In the context of global warming, conducting a comprehensive study on the hydrothermal processes and their influencing factors in the permafrost active layer of the Tibetan Plateau is crucial for gaining a better understanding of the ecohydrological processes in alpine grasslands. In this study, we analyzed differences in soil temperature and humidity change patterns in the active layer of four alpine grassland types in the Totuohe Basin of the Yangtze River source area. We aimed to discuss the influence of vegetation, soil, and other factors on the hydrothermal mechanism of the active layer. The main research results are as follows: (1) Significant differences in the active layer's hydrothermal regime, with higher vegetation cover correlating to lower thaw indices and better moisture conditions. (2) Vegetation and water content strongly influence thermal conditions and active layer thickness. In high-cover alpine meadows, ground surface temperature is lower with a 200 cm active layer, while swamp meadows have a shallowest layer at 160 cm. (3) Deeper active layer moisture is influenced by freezing and thawing, while shallower layers are affected by warm-season precipitation and soil texture. (4) Negative heat fluxes in the topsoil of alpine swamp and high-cover meadows indicate substantial heat release, likely contributing to permafrost preservation due to high active layer water content. New hydrological insights for the region: (1) Vegetation cover significantly influences the thermal and moisture conditions of the active layer, with higher vegetation associated with lower thaw indices and better moisture conditions. (2) Soil moisture distribution within the active layer is controlled by both freeze-thaw cycles and warm-season precipitation, indicating complex interactions between seasonal processes and soil properties.

In 2022, a severe drought and heatwave occurred in the middle and lower reaches of the Yangtze River Basin. Previous studies have highlighted the severity of this event, yet the relevance of soil moisture (SM), as well as vapor pressure deficit (VPD) and vegetation damage, remained unclear. Here, we utilized solar-induced chlorophyll fluorescence (SIF) and various flux data to monitor the impact of drought on vegetation and analyze the influence of different environmental factors. The results indicated a severe situation of drought and heatwave in the Yangtze River Basin in 2022 that significantly affected vegetation growth and the ecosystem carbon balance. SIF and NDVI have respective advantages in reflecting damage to vegetation under drought and heatwave conditions; SIF is more capable of capturing the weakening of vegetation photosynthesis, while NDVI can more rapidly indicate vegetation damage. Additionally, the correlation of SM and SIF are comparable to that of VPD and SIF. By contrast, the differentiation in the severity of vegetation damage among different types of vegetation is evident; cropland is more vulnerable compared to forest ecosystems and is more severely affected by drought and heatwave. These findings provided important insights for assessing the impact of compound drought and heatwave events on vegetation growth.

Compound floods induced by co-occurring multiple drivers may exacerbate the flood impacts and lead to larger flood damage. Exploring future changes in compound flood risk is imperative for flood management and disaster reduction. This study attempts to investigate future changes in compound flood risk across the Yangtze River Basin during 2030 similar to 2100. Future river flow was projected using an improved hydrological model and pairwise series of extremes of rainfall and river flow were extracted from both observed and projected series. Subsequently, stochastic pairs of rainfall and river flow characterizing compound floods were proportionally sampled from their bivariate joint distributions. The damage from each compound flood was obtained from the flood damage function constructed by Random Forests (RF). Further, the expected annual damage (EAD) was calculated to investigate future changes in compound flood risk. Results show that: (1) Future annual maximums of rainfall and river flow are expected to increase by 14.51 % similar to 66.13 % and 1.72 % similar to 55.73 % in the mainstream and northern tributaries, while future annual peak discharge in the southern tributaries (except for the Dongting Lake Basin) is expected to decrease by 4.18 % similar to 12.30 %. A similar spatial distribution of future changes is also found in the bivariate joint distribution of rainfall and river flow. (2) The high coefficient of determination (R-2) of 0.84 indicates the satisfactory simulation and projection capacity of the constructed flood damage function. The positive stepped relationship between flood damage and rainfall or river flow reflects the superposition of multiple flood damage processes. (3) The Han River Basin, the Jialing River Basin, and the two-lakes (the Dongting and Poyang Lakes) area face great threat from compound floods in both historical and future periods. Future compound flood risk is expected to increase by 13.43 % similar to 46.04 % in these regions except for the Poyang Lake Basin, while future risk is expected to increase by 2.03 % similar to 46.04 % in the whole basin. The findings help improve the understanding of future flood risk variations in the Yangtze River Basin and provide essential information for damage reduction.

Bank failures in alluvial rivers are a typical soil-water interaction problem, which is related to many factors including the direct action of flow, river stage change, and human actions (such as bank revetment). To investigate the failure mechanism of protected riverbanks and possible factors affecting their stability, we analyzed data measured from a typical reach of the Middle Yangtze River. Furthermore, we performed numerical simulations of seepage and stress variation inside the riverbank. The field observation and simulated results indicated that: (1) Hydraulic erosion by near -bank flow remains the primary factor influencing the erosion of the protected riverbank. However, the bank protection works effectively limit the lateral bank retreat but increase the incision of the nearby riverbed, with the largest erosion depth of 10.6 m during August to November in 2020. (2) The initial damage in protected banks may be triggered by local tensile stress concentration during the water-rising period, under the combined actions of hydrostatic confining force, pore water pressure and gravity. This initial damage will progress into more severe bank failure events, particularly during the flood period. (3) After the regulation of the Three Gorges Project, the increased changing rate of river stage (similar to 1.6-2.5 fold) could potentially increase the risk of damage to protected riverbanks in the Middle Yangtze River.

The Yangtze River Source Region (YaRSR) is located in the third polar region, the most threatened zone by global warming after the Arctic. Permafrost covers eighty percent of the total area of YaRSR, while the rest is seasonally frozen ground. Due to a significant rise in air temperature, degradation of the permafrost could occur. Permafrost coverage in a river basin greatly controls its hydrology. This study focuses on hydrological modeling in this permafrost environment using the Soil and Water Assessment Tool (SWAT). The SWAT model was calibrated (1985-2000) and validated (2001-2015) on a daily time step. The results were also compared on a monthly time scale. An impermeable layer was introduced within the SWAT model to represent the permafrost conditions. The streamflow is strongly dependent on the seasonal variation of precipitation and temperature, and the rising limb of the hydrograph shows the melting of snow, the contribution of soil water, and thawing of permafrost during the spring-summer season. The permafrost layer well restricted the deep percolation of water. During the spring season, streamflow mainly consists of surface runoff because of the frozen soils. Permafrost and frozen ground thawing lead to an increase in the contribution of groundwater flow to streamflow. Ultimately, the frozen ground depletes as the temperature gets close to the freezing point. This study also describes the SWAT model appli-cation to better analyze and understand the hydrology of the permafrost/frozen ground with limited data availability.

The carbon release and transport in rivers are expected to increase in a warming climate with enhanced melting. We present a continuous dataset of DOC in the river, precipitation, and groundwater, including air temperature, discharge, and precipitation in the source region of the Yangtze River (SRYR). Our study shows that the average concentrations of DOC in the three end-members are characterized as the sequence of groundwater > precipitation > river, which is related to the water volume, cycle period, and river flow speed. The seasonality of DOC in the river is observed as the obvious bimodal structure at Tuotuohe (TTH) and Zhimenda (ZMD) gauging stations. The highest concentration appears in July (2.4 mg L-1 at TTH and 2.1 mg L-1 at ZMD) and the secondary high value (2.2 mg L-1 at TTH 1.9 mg L-1 at ZMD) emerges from August to September. It is estimated that 459 and 6751 tons of DOC are transported by the river at TTH and ZMD, respectively. Although the wet deposition flux of DOC is nearly ten times higher than the river flux, riverine DOC still primarily originates from soil erosion of the basin rather than precipitation settlement. Riverine DOC fluxes are positively correlated with discharge, suggesting DOC fluxes are likely to increase in the future. Our findings highlight that permafrost degradation and glacier retreat have a great effect on DOC concentration in rivers and may become increasingly important for regional biogeochemical cycles.