[Objective] Under the influence of the subtropical monsoon climate, drought-flood abrupt alternation(DFAA) events frequently occur in the middle and lower reaches of the Yangtze River Basin(MLRYRB), posing a serious threat to the sustainable development of the river basin. Therefore, accurately identifying and analyzing the evolution patterns and causes of DFAA events is of great significance for formulating regional disaster prevention and mitigation strategies. [Methods] The short-cycle drought-flood abrupt alternation index(SDFAI) was employed as an indicator for identifying DFAA events to examine the spatiotemporal characteristics of drought-to-flood(DTF) and flood-to-drought(FTD) events in the middle and lower reaches of the Yangtze River, including their frequency, spatial extent, and intensity. Furthermore, the multiscale geographically weighted regression(MGWR) model and the random forest(RF) model were used to quantify the meteorological and atmospheric circulation factors of DFAA events. [Results] The result showed that:(1) DTF and FTD events occurred alternately, with the annual maximum intensity of DTF events showing a decreasing trend and that of FTD events showing an increasing trend, indicating a shift from DTF-dominated to FTD-dominated patterns.(2) The number of occurrences of both DTF and FTD events was primarily concentrated between 22 and 26 times, with the slight events exhibiting the broadest spatial extent and moderate-intensity events being the most frequent. Spatially, western Hunan, southern Anhui, and southern Jiangsu were DTF-prone areas, while southern Hunan and southern Hubei were more susceptible to FTD events.(3) Temperature(TRE) and precipitation(PRE) were the dominant meteorological drivers of DFAA events, serving as the primary or secondary influencing factors in more than 50% of the region. However, sunshine duration(SSD) was the primary influencing factor for FTD events in 29.12% of the region. The El Ni1o-Southern Oscillation(ENSO)and Sunspot were the major atmospheric circulation factors influencing DFAA events. [Conclusion] Compared to FTD events, DTF events exhibited greater intensity, frequency, and spatial extent in the MLRYRB. Hunan, central Hubei, and southern Anhui are regions with frequent occurrences of DFAA events. TEM and PRE are the dominant meteorological drivers of DFAA events, while the ENSO and Sunspot were the key atmospheric circulation factors. These findings can provide scientific guidance for improving the monitoring, prediction, and management of DFAA events in this region.

[Objective] In the context of global climate warming, extreme weather events occur with increasing frequency in the Dongting Lake Basin, and compound drought and heatwave events(CDHEs) exacerbate their influence on socioeconomy and the ecological environment. Analyzing the spatiotemporal evolution patterns of the CDHEs in the Dongting Lake Basin and their response to atmospheric circulation factors is of great significance for regional disaster prevention and mitigation. [Methods] Based on daily maximum temperatures, Standardized Precipitation Evapotranspiration Index(SPEI), and atmospheric circulation indices from 1971 to 2020, trend analysis and wavelet coherence analysis were employed to analyze the spatiotemporal evolution patterns and atmospheric circulation driving mechanisms of CDHEs in the Dongting Lake Basin. [Results] The results showed that from 1971 to 2020, the annual maximum daily temperature in the Dongting Lake Basin showed a significant increasing trend, with a rate of 0.28 ℃/10 a. The SPEI showed substantial interannual fluctuations, with no clear pattern. Droughts were relatively frequent and persistent, occurring during 1983—1988 and 2003—2009. The number of days and duration of CDHEs in the river basin demonstrated increasing trends, with the number of days increasing at rates of 2.2 d/10 a, 1.3 d/10 a, 0.3 d/10 a, and the duration increasing at 0.9 d/10 a, 0.6 d/10 a, 0.2 d/10 a, respectively, exhibiting significant interdecadal variation characteristics. Seasonally, CDHEs mainly occurred in July and August. In the latter 25 years, the number of days and duration of these events increased compared to the former 25 years. Spatial frequency variations exhibited an “increase in the east and decrease in the west” pattern. The northeastern region showed the most significant increase, exceeding 200%. The frequency of CDHEs was influenced by multi-scale atmospheric circulation factors, among which the El Ni1o-Southern Oscillation(ENSO), Pacific Decadal Oscillation(PDO), North Atlantic Oscillation(NAO), and Western Pacific Subtropical High(WPSH) demonstrated more significant influence. [Conclusion] From 1971 to 2020, the number of days and duration of CDHEs in the Dongting Lake Basin showed increasing trends, with significant spatial distribution differences. An overall increasing trend was observed in the east, while the decreasing areas were mainly located in the west. Atmospheric circulation factors such as ENSO, PDO, and NAO were important influencing factors of the occurrence of CDHEs. These findings provide a scientific basis for regional compound disaster risk assessment and adaptive management.

[Objective] To analyze the spatiotemporal variations of meteorological and hydrological droughts in the Hengjiang River Basin under climate change, and to inform drought mitigation and water resource management. [Methods] Four CMIP6 climate scenarios(SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5) under the CMIP6 framework were selected, and the Soil and Water Assessment Tool(SWAT) model was applied to estimate runoff in the Hengjiang Basin. Based on the standardized precipitation index(SPI), standardized runoff index(SRI), and Copula function, the joint distribution characteristics of meteorological and hydrological droughts in the Hengjiang River Basin during the historical period(1980—2014) and the projected period(2015—2100) were analyzed. [Results] The SWAT model demonstrated strong applicability in the Hengjiang River Basin, with calibration and validation result showing R², NSE, R_e values of 0.91, 0.90, and-0.01(calibration), and 0.96, 0.89, and 0.13(validation), respectively. During the historical baseline period(1980—2014), the river basin exhibited an intensifying trend of meteorological and hydrological droughts, with annual average precipitation and runoff decreasing simultaneously. The annual average SPI and SRI values approached mild drought levels(-0.44). The frequencies of severe and mild meteorological droughts increased across the river basin, while the frequencies of moderate to severe hydrological droughts significantly rose in most regions, accompanied by occasional extreme drought events. During the projected period(2015—2100), precipitation and runoff were projected to increase significantly, leading to an overall alleviation of meteorological and hydrological droughts. The frequency of mild meteorological droughts was expected to increase significantly, while the frequencies of moderate and severe meteorological and hydrological droughts were projected to decrease substantially. However, the frequency of extreme meteorological and hydrological drought events was anticipated to increase. In the Hengjiang River Basin, short-term drought risks(return period <2 years) would decrease, with meteorological and hydrological drought intensities tending to converge. However, in the long term(return period >10 years), the lagged response of hydrological drought to meteorological drought was expected to intensify. [Conclusion] In the future, the Hengjiang River Basin is projected to become increasingly humid, with both meteorological and hydrological droughts alleviated. Therefore, while addressing meteorological and hydrological droughts in this river basin, measures should also be strengthened to address the trend toward increased humidity, enhance water resource planning and management capabilities, and improve flood control and waterlogging prevention capacities.

[Objective] Construction disturbances from projects such as transportation infrastructure in mountainous areas are often unavoidable and may increase the risk of flash flood-debris flows in the affected areas. Scientifically identifying and evaluating the impact of construction disturbances on the disaster-forming risk of flash flood-debris flows is conducive to preventing induced natural disasters. [Methods] The 2023 “8·21” flash flood-debris flow disaster in Jinyang, Sichuan was taken as a case study. Based on field investigations and remote sensing interpretation, the forms of construction disturbances were analyzed, and a scenario-based simulation comparison method was proposed to identify the amplification effect of construction disturbances on flash flood-debris flow risk. The risk amplification effect result ing from the superposition of construction material sources in this event was elucidated. [Results] The results showed that:(1) supplying short-range direct material sources and occupying flood discharge areas were the main forms through which construction disturbances affected the disaster-forming risk of flash flood-debris flows, respectively increasing the disaster-forming risk degree and the vulnerability of affected areas.(2) In the disaster occurring in Jinyang, Sichuan, the supply of construction-induced material sources caused the maximum burial depth at the disaster-forming cross-sections to increase by 2.65 m, which was the direct cause of the severe destruction of temporary construction housing.(3) The construction disturbances in this event caused the disaster-forming risk of the temporary housing to increase from a 50-year return period to a 20-year return period, significantly amplifying the disaster-forming risk of flash flood-debris flows. [Conclusion] The scenario-based simulation comparison method can effectively identify the amplification effect of construction disturbances on flash flood-debris flow risk. It emphasizes that during transportation construction in mountainous areas, the placement of temporary housing on the concave banks of gently widening river sections should be avoided. Reducing disturbances to bank slopes and enhancing bank slope erosion protection can significantly suppress the amplification effect of disturbances on the disaster-forming risk of flash flood-debris flows.

[Objective] Research on the chain risk transmission effects of disaster chains is an important prerequisite for formulating short-term emergency response and recovery strategies, as well as medium-to long-term prevention strategies. Systematically reviewing the development trajectory of existing research in China can clarify the future research directions in the field of disaster chains and optimize frontline disaster mitigation capabilities. [Methods] A systematic timeline-based review is conducted on over 300 papers published in Chinese core journals between 1987 and 2024 and 143 SCI-indexed papers published since 2007, all authored by scholars affiliated with Chinese institutions. [Results] The result show that:(1) over the past 38 years, research on disaster chains in China has gone through three development stages: discussion of disaster chains and related extended concepts, research on chain process deduction, and development of impact assessment method and quantitative models.(2) Existing studies primarily focus on qualitative reasoning of chain structures, while quantitative research on chain risk diffusion and transfer impact is becoming a current hotspot.(3) The studied disaster types are mostly concentrated on earthquake and geological disasters, with some result of qualitative reasoning and quantitative assessment for disasters such as rainstorms, floods, and droughts, though such studies remain relatively limited overall. The assessment of the benefits of chain-breaking disaster mitigation based on chain risk diffusion networks needs to be strengthened. Future research can consider incorporating the synergistic effects of existing disaster mitigation resources into chain risk mitigation assessment. [Conclusion] The results indicate that to better support frontline disaster prevention and mitigation, theoretical and quantitative empirical research in the field of disaster chains can be improved from four aspects: historical disaster events, disaster system science, three-dimensional monitoring networks, and the application of chain-breaking disaster mitigation strategies. These findings can provide references for researchers to accurately identify research directions in the field of disaster chains.

[Objective] To investigate the characteristics of urban waterlogging response under the combined influence of wind fields and rainstorms in densely built mountainous cities. [Methods] Taking a drainage area in Yuelai New City of Chongqing as the study area, a rainfall-runoff process simulation method under the combined influence of wind and rainfall was proposed based on the Storm Water Management Model(SWMM) and the LISFLOOD-FP model. Rainfall design was carried out based on seven rainstorm patterns. Using historical observed wind fields, the most adverse wind direction leading to the maximum runoff yield and overflow in the study area was simulated. The urban waterlogging response characteristics under the combined influence of wind fields and rainstorms were systematically analyzed. [Results] The result showed that when the wind direction was 225°(with due north as 0°), the runoff yield and overflow volumes in the study area were significantly higher than those under other wind directions, and the influence of wind direction intensified with increasing rainfall intensity. Under the influence of three wind field types(with average wind speeds of 0~2 m/s for light wind, 2~4 m/s for moderate wind, and 4~6 m/s for strong wind), the waterlogged area increased by an average of 1.6%~6.5% compared with no wind field conditions, with local increases exceeding 9.0%. Compared with the waterlogged area, the changes in overflow onset time and overflow peak became more pronounced with increasing return periods. Under the influence of wind fields, the waterlogged area increased most significantly under rainfall Pattern Ⅲ when the return period was less than 50 years, while the increase was more pronounced under Pattern Ⅱ when the return period exceeded 50 years. Changes under uniform and bimodal rainstorm patterns were relatively minor. [Conclusion] In simulating urban waterlogging in densely built urban districts, neglecting the influence of wind fields may underestimate both runoff yield and waterlogging severity. The proposed method for rainfall-runoff simulation coupled with wind field influence demonstrates strong applicability in simulating waterlogging in mountainous cities.

[Objective] Accurate and reliable flood forecasting is one of the important non-engineering measures for flood control and disaster reduction. Improving the accuracy and reliability of inflow flood forecasting for the Guxian Reservoir using deep learning technologies is of great importance for flood control and dispatch decision-making. [Methods] A deep learning-based flood process probabilistic forecasting model, Transformer-Bootstrap, was constructed by coupling the output layer of the Transformer model with the Bootstrap interval prediction method. Using the observed rainfall-runoff data from the Lushi Hydrological Station, which controls the catchment area of the Guxian Reservoir for the period 1990—2016, and applying the Chapman filtering method for baseflow separation, 49 hourly flood event datasets were obtained. Of these, 39 flood events from 1990 to 2010 were used for training, while 10 flood events from 2011 to 2016 were used for validation. The model's performance was evaluated using metrics such as Nash-Sutcliffe Efficiency(NSE), Root Mean Square Error(RMSE), bias, and Coefficient of Determination(R²). [Results] The result showed that for forecast lead times of 1~6 hours, the NSE for the training period decreased from 0.98 to 0.92, while the NSE for the validation period decreased from 0.89 to 0.55. Forecast errors showed an increasing trend, with RMSE and bias for the training period increasing from 31.54 m³/s to 64.04 m³/s and from 9.08% to 24.05%, respectively, while RMSE and bias for the validation period increased from 11.01 m³/s to 20.57 m³/s and from 3.90% to 11.36%, respectively. The model began to improve after approximately 75 iterations and only approached convergence after more than 175 iterations. During the validation period, the PIPC value of the forecast decreased from 89.5% to 61.6%, and the PINAW value increased from 0.008 to 0.076. Particularly, as the forecast lead time increased to 4~6 hours, the bias between the forecast and observed discharge became larger, leading to poorer forecast performance. [Conclusion] The Transformer-Bootstrap model demonstrates good performance for short lead times(1~3 hours), with NSE values exceeding 0.80 for both the training and validation periods. The probabilistic forecast coverage for the Transformer-Bootstrap model generally exceeds or is close to the 90% confidence level interval, and the probabilistic forecast result are reasonably reliable. However, as the lead time increases, the forecast accuracy decreases, and forecast errors increase. Additionally, the model requires more iterative calculations to converge, with the forecast accuracy and stability during the training period superior to those during the validation period. A key scientific issue for future research is how to improve the accuracy and robustness of deep learning flood forecasting models for longer lead times. The findings provide technical support for flood control and disaster reduction in the Guxian Reservoir and parts of the middle reaches of the Yellow River.

[Objective] Miyun Reservoir, as the core strategic water reserve for the Beijing-Tianjin-Hebei region, has current scheduling rules that exhibit limitations in handling medium and small floods, such as insufficient refined regulation and control, as well as water levels at the end of the main flood season often falling below the reservoir's restricted levels for the post-flood period. This result in compromised storage benefits, and the constrained dynamic regulation capacity of water resources makes it difficult to balance flood control and storage benefits. To enhance both safety and resource utilization efficiency in medium and small flood scheduling, it is necessary to extract and optimize the scheduling rules. [Methods] A scheduling model for medium and small floods based on model predictive control(MPC) was constructed. For four flood magnitudes, 11 graded release strategies were designed as scheduling rules, and 44 scenarios were simulated and compared to identify the optimal scheduling scheme. Additionally, simulations for the probable maximum flood(PMF) and a 10 000-year return period flood were performed to validate the model's applicability under extreme conditions. [Results] The result showed that for a 2-year return period flood, retaining the entire flood volume was sufficient. For a 5-year return period flood, the maximum outflow decreased from 554 m³/s under the original rules to 244 m³/s, representing a reduction of 56%. The number of gate operations decreased from 82 to 19, a reduction of 76.8%. For the 10-year and 20-year return period floods, optimization was achieved to varying degrees. On average, for floods with return periods of 5 years and above, the maximum outflow was reduced by 25%~30%, the final water level stabilized within the target range of 154±0.1 m, the comprehensive evaluation score improved by 15%~30% compared with the original rule, and the number of gate operations decreased by over 60%. [Conclusion] While adhering to existing scheduling principles, optimized scheduling of small and medium floods can be achieved through model-based simulation. This approach strikes a balance between flood control and water utilization, while effectively reducing the operation and maintenance costs for management units. The findings provide a reference for optimizing flood scheduling in similar reservoirs with large storage capacities and significant differences in scheduling tiers.

[Objective] Under the background of global warming, the frequent occurrence of high-temperature events has posed a serious threat to the water quality safety of urban drinking water sources. The objective is to clarify the mechanisms by which high-temperature events affect the water quality of urban drinking water source reservoirs, and to explore the effects of reservoir storage capacity and scheduling strategies on water quality changes during high-temperature periods. [Methods] Taking 16 drinking water source reservoirs in Nanjing, a major city in the lower reaches of Yangtze River, as the research objects, the monthly long-term data from 2000 to 2023, on 24 physicochemical water quality indicators and meteorological data were used. Spearman correlation analysis was conducted to reveal the long-term associations between key water quality indicators and temperatures. The response mechanisms and spatial variation patterns of reservoir water quality were analyzed in combination with the extreme high-temperature event in 2022. [Results] The result showed that only 8 indicators—water temperature(T), pH, permanganate index(COD_Mn), dissolved oxygen(DO), fecal coliform(FC), total phosphorus(TP), total nitrogen(TN), and ammonia nitrogen(NH₃-N)—were significantly correlated with temperature in certain reservoirs(p<0.01). The typical high-temperature events in August 2022 led to an average increase of 6.5% in T and a decrease of 5.9% in DO across the reservoirs, while TP and TN increased by 18.8% and 15.6%, respectively. Spatial variation analysis revealed that reservoirs in northern Nanjing, characterized by smaller average storage capacity and greater water level decline, had significantly higher increases in TN and TP(21.8% and 15.5%) compared to those in the southern region. In contrast, reservoirs in southern Nanjing with larger average storage capacities showed more pronounced changes in DO, pH, COD_Mn, FC, and NH₃-N. [Conclusion] High temperatures exacerbate water quality deterioration by altering thermal stratification structures and biogeochemical processes in water bodies. Reservoir storage capacity and water scheduling strategies significantly regulate water quality response, with small-capacity and rapid water-level-declining reservoirs being more vulnerable to high-temperature stress. It is recommended that a classification-based management model should be established based on scheduling functions and response characteristics, and differentiated regulation strategies should be developed to enhance the climate resilience of water supply systems in large cities.

[Objective] Leakage in direct drinking water pipelines has long been a persistent challenge in China's water supply industry. It not only affects residents' normal water usage but also leads to substantial drinking water waste and brings significant economic losses to water supply enterprises. Current leakage detection technologies face challenges such as high equipment costs, insufficient intelligence levels, and imbalanced data categories. [Methods] To address these issues, a low-cost pipeline leakage early warning model based on the principle of constant pressure water supply was proposed. Building upon the principle of constant pressure water supply, the dynamic changes in operational parameters of water supply frequency converter, such as frequency, voltage, current, and rotational speed, were used to establish the SMOTE-ENN-GWO-SVM leakage early warning model by integrating intelligent algorithms and machine learning technologies. The SMOTE algorithm was used to perform oversampling on the sample data to balance the class distribution, the Edited Nearest Neighbors(ENN) algorithm was applied to clean noisy samples, and the grey wolf optimizer was used to adjust the key hyperparameters of the support vector machine(SVM) to enhance model performance. [Results] The result showed that the SMOTE-ENN-GWO-SVM model achieved an accuracy of 98.16% and an F1 score of 0.952 3, both outperforming the comparative models. [Conclusion] This method significantly improves the accuracy and robustness of leakage detection. Its characteristics of low cost and high precision meet the practical application requirements for responsive and reliable leakage detection in direct drinking water systems, providing technical support for improving the efficiency of urban water resource management.

[Objective] To address the risks of power shortage or water abandonment in hydro-wind-PV complementary systems under continuous extreme new energy output events, and to coordinate the mid-term scheduling risks and long-term power generation benefits of the system, a long-term optimized scheduling method for hydro-wind-PV complementarity considering extreme new energy output is proposed. [Methods] First, extreme new energy output scenarios were defined, and samples were extracted from multi-year historical data to reveal the characteristics of extreme new energy output. Second, a scheduling risk assessment method for hydro-wind-PV systems under extreme new energy scenarios was developed. Finally, a multi-objective optimization model for hydro-wind-PV complementarity was established, considering both power generation and scheduling risks to enhance the system's response capability to extreme new energy events, and it was validated using the Beipan River Clean Energy Base as a case study. [Results] The result showed that taking a normal year as an example, before optimization, the maximum power shortage risk reached 0.75×10⁸ kWh in the pre-flood stage, while the maximum power curtailment risk reached 0.31×10⁸ kWh in the post-flood stage. Compared with the power-generation-optimal solution, the balanced scheme reduced scheduling risk by 0.48×10⁸ kWh and decreased power generation by 0.17×10⁸ kWh. Compared with the risk-optimal solution, the balanced scheme increased scheduling risk by 0.21×10⁸ kWh while improving power generation by 0.66×10⁸ kWh. The proposed model recommended controlling the water level of Guangzhao Reservoir within 692.15~694.93 m in the pre-flood stage and 743.84~745.00 m in the post-flood stage. [Conclusion] The hydro-wind-PV system shows significant limitations in flexible regulation performance. The proposed multi-objective optimization model can effectively coordinate power generation benefits and scheduling risks under extreme new energy scenarios. The key-node water level intervals corresponding to the Pareto front set can serve as reasonable water level control ranges. The balanced scheme demonstrates excellent performance in balancing power generation benefits and risk control and achieves a significant reduction in scheduling risks at the expense of only a small loss in generation, thereby providing valuable guidance for formulating scheduling strategies against extreme new energy output.

[Objective] Due to the complexity of high-altitude environments and the combined effects of climate change and human activities, the mechanisms of runoff variations on the northern slope of the Kunlun Mountains have become one of the core challenges in current hydrological research in arid regions. The coordinated evolution patterns of climatic and hydrological processes on the northern slope of the Kunlun Mountains(covering Hotan River, Keriya River, and Cherchen River basins) from 1956 to 2023, as well as their underlying influencing factors, are investigated, aiming to provide decision-making support for the sustainable management and scientific allocation of water resources in cold and arid regions. [Methods] Based on high-resolution meteorological and hydrological databases, and combining methods including linear regression analysis, moving average analysis, and anomaly analysis, the long-term trends, spatial clustering, and driving mechanisms of regional temperature, precipitation, and runoff were revealed. [Results] The results indicated that(1) the region showed significant accelerated warming, with a warming rate of 0.313~0.375 ℃/10 years, significantly higher than the global and national average values. It was primarily driven by the elevation-dependent warming effect and the decrease in surface albedo caused by snow and ice melting.(2) Precipitation generally exhibited a linear increasing trend(1.17~11.8 mm/10 years), but due to the weakening of westerly moisture transport, precipitation in the eastern region shifted to a decreasing trend after 2020.(3) Runoff increased significantly after the 1990 s(with an increase of over 30% after 2010). Decoupling analysis based on Z-score standardization confirmed that temperature contributed far more to runoff than precipitation. Runoff primarily depended on short-term replenishment from accelerated glacial melting, showing a high degree of synchrony with temperature changes, whereas the precipitation-runoff response exhibited a lag, which might be related to groundwater storage and regulation.(4) Hydrological responses differed significantly between the eastern and western regions. The precipitation-to-runoff conversion efficiency remained stable in western river basins, whereas that in eastern river basins experienced distinct decoupling after 2020. [Conclusion] The northern slope of the Kunlun Mountains shows an extreme “temperature-controlled” response pathway, and climate change has significantly reshaped the regional hydrological patterns. Therefore, it is necessary to develop a monitoring and early warning system targeting peak glacial melting, revise water conservancy engineering standards, and optimize water resource allocation strategies, so as to cope with future runoff decline risks and ensure regional water and ecological security.

[Objective] As a typical wetland ecosystem in the middle and lower reaches of the Yangtze River, the area surrounding Dongting Lake plays a vital role in regional ecological security and flood mitigation. The spatiotemporal variation characteristics of vegetation cover in the area surrounding Dongting Lake are investigated, and the influencing factors are further analyzed, aiming to provide a scientific basis for the dynamic monitoring and integrated management of ecosystems in lake areas. [Methods] The normalized difference vegetation index(NDVI) was used as the primary indicator of vegetation cover changes. Combined with terrestrial water storage anomaly(TWSA) data derived from spherical harmonic products from the Gravity Recovery and Climate Experiment(GRACE) satellites and multi-source meteorological data, the spatiotemporal characteristics of vegetation change in the area surrounding Dongting Lake from 2003 to 2022 were systematically analyzed. The driving mechanisms behind the influencing factors of NDVI were investigated. [Results] (1) From 2003 to 2022, the annual average NDVI in the area surrounding Dongting Lake ranged between 0.49 and 0.56, with an interannual increase rate of approximately 0.002 4/yr.(2) Spatially, NDVI showed significant increases in the northwest and southeast, with NDVI change rates gradually decreasing from these regions toward the central region of the lake area.(3) During the study period, five moderate or more severe hydrological drought events were identified based on water storage deficit index(WSDI), with a total duration of 26 months and a cumulative terrestrial water storage deficit of 3551 mm. During the five hydrological drought events, NDVI anomalies were all negative, indicating that water storage deficits suppressed vegetation growth. NDVI responded rapidly to precipitation variations. NDVI responded to temperature variations with a lag of about one month, yet it occurred one month earlier than its response to TWSA. El Ni1o-Southern Oscillation(ENSO) indirectly affected vegetation by modulating atmospheric circulation, and vegetation showed a significant long-term lagged response to ENSO. [Conclusion] The annual average NDVI in the area surrounding Dongting Lake exhibited an overall fluctuating upward trend from 2003 to 2022, indicating improved regional vegetation cover under ecological conservation policies. Precipitation and temperature are identified as the primary climatic factors of vegetation growth. Notably, TWSA, as a comprehensive indicator reflecting surface water, groundwater, and soil moisture, plays a significant regulatory role in vegetation dynamics.

[Objective] Reactive silicon is irreplaceable in certain biological structures, thereby influencing primary productivity and ecosystem stability. River dam construction profoundly alters the biogeochemical processes of nutrients in water, constraining river hydrological processes and ecosystem evolution. It is necessary to improve the understanding of the biogeochemical cycle of silicon in rivers through dam construction. [Methods] Based on a review of relevant studies, the migration and transformation mechanisms of riverine reactive silicon were taken as breakthrough points, with a focus on the retention effects of damming and its ecological impacts, the migration mechanism of reactive silicon after damming, and the biogeochemical processes of reactive silicon under specific damming patterns. [Results] Damming increased the retention of riverine reactive silicon, [Results]ing in negative ecological effects such as changes in biological community structure. Weakened rock weathering, intensified sedimentation and biological uptake and transformation, and the evolution of stratified density currents were key factors influencing reactive silicon migration, but the importance of each factor varied across different river regions. In rivers with cascade dams, the environmental behavior of reactive silicon was regulated by multiple complex pathways. The “reservoir-in-reservoir” effect caused by the construction of ecological regulating dams might alter key processes driving the reactive silicon cycle. [Conclusion] A comprehensive understanding of the specific mechanisms by which damming affects reactive silicon still requires further research. Future research is recommended to focus on dynamic monitoring and model development, multidimensional ecological impact assessments, mechanisms of stratified density currents, cross-regional comparisons, and the environmental behavior of reactive silicon under different operation patterns. The result deepen the understanding of the migration and transformation processes of riverine reactive silicon affected by dam construction and can provide guidance for the ecological management of river damming.

[Objective] Investigating the impact of climate change and permafrost degradation on runoff components in the Hailar River Basin is important for revealing hydrological evolution mechanisms and optimizing adaptive water resource management strategies in river basins of cold regions. [Methods] Using hydrological, meteorological, and permafrost observation data from 1980 to 2012, runoff components were partitioned using the digital filtering method. Permafrost variation characteristics were simulated using the Stefan model, and the relative contributions of precipitation, air temperature, permafrost depth, and vegetation cover to variations in runoff components were analyzed using the grey relational analysis method. [Results] The result showed that:(1) runoff in the river basin decreased significantly during the study period. The reduction rate at each station ranged from 15.5 mm·(10a)^-1 to 43.6 mm·(10 a)^-1, and baseflow accounted for over 70% of total runoff.(2) The Stefan model performed well in simulating the annual maximum frozen depth in the river basin. The maximum frozen depth showed a significant decreasing trend at a rate of 8.8~11.2 cm·(10 a)^-1.(3) The grey relational analysis result revealed that cold-season runoff had the highest correlation degree with permafrost, ranging from 0.78 to 0.83, while warm-season runoff had the highest correlation degree with vegetation coverage, ranging from 0.79 to 0.84. Air temperature showed a relatively low correlation degree at all stations, ranging from 0.60 to 0.69. [Conclusion] The result indicate that:(1) runoff and its components in the river basin exhibit a significant declining trend during the study period, with baseflow playing a dominant role in the changes in total runoff.(2) The Stefan model is applicable in simulating the annual maximum frozen depth in the river basin. Overall, permafrost degradation across the river basin is severe and exhibits significant spatial heterogeneity.(3) Cold-season runoff is primarily affected by permafrost degradation, while warm-season runoff is mainly controlled by vegetation cover, showing pronounced seasonal differences. Air temperature affects runoff indirectly by influencing permafrost thaw and vegetation growth.

[Objective] During the construction of concrete dams, the increased safety risks due to three-dimensional intersecting operations and limited construction areas, along with the lack of depth information in traditional two-dimensional monitoring, make it difficult to accurately determine the relative positions of personnel and machinery. Consequently, the effectiveness of construction safety early warnings is limited. To address the scale uncertainty in monocular vision-based ranging and enhance the human-machine collision risk identification and real-time warning capabilities for dam surface construction, a construction safety early warning method based on monocular visual depth perception is proposed. [Methods] A three-dimensional ranging model was constructed by integrating YOLOv10 target detection with MiDaS monocular depth estimation. Real-time calculation of the 3D Euclidean distance was achieved through target identification, depth estimation, and spatial coordinate conversion, and a warning mechanism based on spatiotemporal joint criteria was established by combining depth maps and safety thresholds. To verify the effectiveness of the method, comparative experiments with mainstream monocular depth estimation models were designed, and case tests were conducted based on a hydropower engineering project in Sichuan. [Results] The experimental result showed that the model achieved a root mean square error(RMSE) of 27 cm in measuring the height of concrete buckets and 35 cm in detecting the relative distance between humans and machines. The processing time per frame was 0.05 s, meeting the requirements for real-time monitoring at dam surface construction sites. Compared to traditional two-dimensional video method, the model demonstrated significant advantages in both the accuracy and real-time performance of risk identification. [Conclusion] A construction safety early warning method based on three-dimensional ranging is established, enabling three-dimensional risk monitoring and hazard warning for concrete dam surface construction. This method not only serves dam surface construction scenarios but also has the potential to be extended to human-machine coordinated operations and construction digital twin systems, providing a reference for achieving higher levels of multi-target early warning and dynamic protection in the future.

[Objective] The study aims to investigate the dynamic stress characteristics and fatigue damage mechanisms of turbine runner blades under complex operating conditions. [Methods] Based on field test data, Fourier transform(FT) technology was used to perform time-domain and frequency-domain analysis of stress signals at key parts(such as blade root and outlet edge) of the Francis turbine runner. The stress response characteristics of these key parts of blades were systematically investigated during variable load, no-load, and start-stop transient processes. [Results] The result showed that under variable load conditions, the maximum static stresses at measurement points 7FSG12 and 13FSG1 reached 27.56 MPa and 25.99 MPa, respectively, while the maximum dynamic stresses at measurement points 13FSG2 and 13FSG14 were 13.19 MPa and 13.04 MPa, respectively. Furthermore, the dynamic stress distribution at the junction of the blade and the lower ring showed a decreasing trend from the inlet edge to the outlet edge, specifically manifested as 7FSG10 > 7FSG8 > 7FSG6. Under the 320 MW condition, the dynamic and static stresses at most measurement points were lower than those under the 290 MW and 300 MW conditions. [Conclusion] The result show that significant stress concentration is observed in the connection zone between the runner blade and the upper crown(especially near the outlet edge), which is highly consistent with the actual crack initiation zone. It is recommended to add a stress-reduction triangular block to improve stress distribution. The intensity of the rotor-stator interaction effect decreases with increasing distance from the blade-free zone. The unit is capable of short-term safe power overgeneration under the condition of 320 MW over-rated output. However, it should be noted that the alternating stress amplitude on the blade under start-stop and no-load conditions is significantly higher than that under variable load conditions, and the fatigue damage risk increases sharply with the frequency of start-stop cycles. Therefore, to improve the structural reliability and operational safety of hydraulic units, it is recommended to optimize the operational strategies to minimize unnecessary start-stop operations.

[Objective] Flow resistance characteristics are a core scientific issue in the field of river dynamics, with dual value in linking theoretical innovation and engineering practice. They not only provide theoretical support for revealing the mechanisms of water-sediment transport, but also serve as an important foundation for riverbed evolution simulation and flood control. The core objective is to clarify the applicability limitations of existing flow resistance formulas in the special water-sediment environment of the Yellow River, establish a resistance calculation method suitable for the condition of strong scouring and silting of fine particles, and provide technical support for the accurate simulation of riverbed evolution in the Yellow River. [Methods] Firstly, existing flow resistance formulas were systematically reviewed, and relevant formulas based on resistance partitioning were verified. Aiming at the significant deviation problem of verified formulas under the condition of strong scouring and silting of fine particles, the idea of energy slope partitioning was adopted, and a formula framework with the superposition of sand grain resistance and sand wave resistance as the core was constructed. Coefficients in the calculation formulas of sand wave length and height were calibrated through measured data, and a flow resistance formula for the Yellow River based on the energy slope partitioning method was established. The relationship between coefficients and Froude number(Fr) was calibrated using observed data. Finally, the accuracy of the newly established formula and the rationality of the parameters were verified and analyzed through measured data. [Results] Verification result showed that the newly established flow resistance formula had high accuracy, and the calculated result of sand wave height, sand wave length, and the proportion of sand wave resistance were all within reasonable ranges. The resistance coefficient showed a significant negative correlation with the measured sediment-carrying capacity. The calculation result of the formula were consistent with the automatic adjustment pattern of the Yellow River channel, and enabled the reasonable simulation of riverbed evolution in the Yellow River. [Conclusion] It is confirmed that the flow resistance formula constructed based on the energy slope partitioning method can effectively adapt to the special water-sediment environment of strong scouring and silting of fine particles in the Yellow River, and solve the problem of insufficient applicability of traditional formulas in this scenario. The established formula can be used as an effective calculation method for flow resistance in the Yellow River, and provide reliable technical support for the simulation of riverbed evolution in the Yellow River and related engineering practices of flood control.

[Objective] The reservoir-induced earthquakes caused by the impoundment and geological hazards such as reservoir bank landslides triggered by fluctuations in reservoir water level frequently occur. To accurately assess the impact of the Baihetan hydropower station construction on slope stability in the reservoir area, it is imperative to investigate the degradation characteristics of jointed rock masses under the combined action of dry-wet cycles and dynamic loading. [Methods] Based on this, for jointed dolomite and jointed sandstone collected from typical landslides in the Baihetan reservoir area, laboratory tests were conducted to systematically analyze the damage mechanisms of jointed rock masses under dry-wet cycles and dynamic loading, considering different lithologies and damage cycles. [Results] The result showed that under the combined action of dry-wet cycles and dynamic loading, the jointed rock masses rapidly degraded in the first three cycles. The shear strength degradation rates reached 25.5% for jointed sandstone and 22.3% for jointed dolomite. After five cycles, the degradation degree tended to stabilize. Under twelve cycles, the degradation rates of cohesion and internal friction angle of jointed sandstone rock masses reached 22% and 13%, and those of jointed dolomite rock masses both reached 33%. [Conclusion] The result indicate that the degradation of jointed rock masses is primarily controlled by mineral dissolution caused by dry-wet cycles and the abrasion of structural planes induced by dynamic loading. The degradation caused by dry-wet cycles is more pronounced for the jointed sandstone. Under low normal stress, more severe abrasion on sandstone structural planes is caused by the dynamic loading, whereas under high normal stress, higher damage degree of dolomite is caused by the dynamic loading. Under the combined degradation, the shear strength degradation rate of jointed sandstone is greater than that of jointed dolomite. However, this difference in strength degradation rates between the two rock types diminishes with increasing normal stress. The mechanical properties of jointed rock masses are significantly degraded by the combined action of dry-wet cycles and dynamic loading, and affected by lithology, normal stress, and the number of cycles. This provides an important theoretical basis for slope stability assessment and disaster mitigation in the Baihetan reservoir area.

[Objective] The strength degradation and microstructural evolution of structured clay under vibrational disturbance directly affect the stability of foundation engineering. The laws governing microstructural evolution and the mechanisms of strength degradation are revealed, and theoretical and technical support is provided for the analysis and control of foundation stability. [Methods] Structured clays of the Zhanjiang Formation were selected as the research object. Laboratory vibration disturbance tests were conducted, in combination with unconfined compressive strength tests, scanning electron microscopy(SEM) analysis, and nuclear magnetic resonance(NMR) techniques, to investigate the strength response and microstructural evolution of the soil during the disturbance process. The relationship between cumulative disturbance energy and strength degradation was established to reveal the evolution laws of energy, microstructure, and strength of structured clay under disturbance. [Results] The result showed that the disturbance degree, defined based on unconfined compressive strength, exhibited a power-law decreasing trend with increasing cumulative disturbance energy, and demonstrated pronounced damage sensitivity within the energy range from 760.60 J to 3 777.22 J. Microstructural analysis indicated that vibrational disturbance destroyed the original aggregate structure, leading to a more disordered arrangement of soil particles, a significant weakening of cementation, and a reconstructed pore structure characterized by the transformation from aggregate pores to interparticle pores and an increase in porosity. With the accumulation of disturbance, particle rearrangement, cementation damage, and pore reconstruction evolved synergistically, leading to the continuous transformation of microstructural damage into macroscopic strength degradation. [Conclusion] Cumulative disturbance energy accelerates the strength degradation of structured clay by destroying the aggregate structure, weakening interparticle cementation, and reconstructing the pore morphology, thereby forming a dynamic feedback mechanism of “disturbance-structural damage-strength degradation”. This process exhibits pronounced cumulative and sensitive characteristics, exerting a significant influence on foundation stability. A theoretical basis and technical reference are provided for evaluating the disturbance sensitivity of structured clay and for controlling foundation stability in hydraulic engineering.

[Objective] Loess in open water conveyance channels in cold and arid regions of northwest China is commonly subjected to the coupled effects of dry-wet alternation and freeze-thaw cycles, which can induce pore expansion, structural loosening and strength degradation. To reveal the mechanical deterioration mechanism and microstructural evolution of geopolymer solidified loess under dry-wet-freeze-thaw cycles, and to improve the long-term service stability of loess slopes in open channels, the durability of geopolymer solidified loess was investigated. [Methods] Loess collected from an open water conveyance channel in Xinjiang was used as the research object. Geopolymer solidified loess specimens with geopolymer contents of 0%, 5%, 10% and 15% were prepared and subjected to 0 to 12 dry-wet-freeze-thaw cycles. X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy and nuclear magnetic resonance tests were conducted to characterize the mineral composition, micromorphology and pore structure evolution. [Results] Geopolymer significantly improved the strength and resistance of loess to dry-wet-freeze-thaw deterioration, with the 10% geopolymer content showing the best performance. Before cycling, the unconfined compressive strength of the 10% geopolymer solidified loess reached 1.405 MPa, which was 248% higher than that of untreated loess. After 12 cycles, its strength loss rate was 37.12%, markedly lower than the 62.53% of untreated loess. The microstructural result showed that C—S—H and C—A—H gels generated by geopolymerization filled pores and cemented soil particles, transforming the soil from a loose flocculated structure into a dense cemented structure. Dry-wet-freeze-thaw cycles weakened the gel cementation effect, promoted the transformation of small pores into large pores and led to continuous strength degradation. Correlation analysis of pore structure indicated that the number of large pores had the most significant influence on the deterioration of unconfined compressive strength. [Conclusion] Geopolymer can synergistically improve the dry-wet-freeze-thaw resistance of loess through gel filling, particle cementation and pore refinement. A geopolymer content of 10% achieves a favorable balance between strength enhancement and durability improvement. The results provide a scientific basis for the application of geopolymer solidified loess in open channel engineering.