[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 Niño-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 study the movement characteristics and key influencing parameters of debris flow,construct a debris flow disaster risk prediction model,and provide data support for assessing the disaster risk of transportation infrastructure caused by debris flows.[Methods]Taking the debris flow disaster in Wei Ziping Village,Xi'an City,Shanxi Province as the research object,a debris flow movement model based on the depth-integrated continuum mechanics theory was established.The friction coefficient and debris flow discharge were selected as key parameters to explore the variation laws of debris flow velocity and mud depth in the accumulation area,and evaluate the risk level of the area where the debris flow exits the gully.Combined with the multiple linear regression,polynomial regression and support vector machine models,the prediction equations for the relationship between debris flow discharge,friction coefficient and flow velocity,and mud depth were established.[Results]There is a significant positive correlation between the flow velocity and the flow rate of debris flow.The flow velocity fluctuates under different flow rate conditions,with the maximum flow velocity ranging from 2.58 m·s-1 to 8 m·s-1.The mud depth keeps increasing with the increase of flow rate,and the maximum mud depth range is 0.5 m to 4 m.The friction coefficient is negatively correlated with both the flow velocity and the mud depth of the debris flow.With the increase of the friction coefficient,the maximum flow velocity and the maximum mud depth show an overall downward trend.The risk prediction result show that the risk of debris flow increases significantly with the increase of debris flow.The increase of the friction coefficient can effectively reduce the risk,and the effect is significant at a lower debris flow,while the effect of frictional resistance is not significant at a larger debris flow.The support vector machine model has a better prediction effect on the maximum flow velocity of debris flow,while the polynomial regression model has the best prediction effect on the maximum mud depth in the debris flow accumulation area.[Conclusion]Monitoring the flow of debris flows to predict the flow velocity and the depth of the accumulated sediment in the affected area plays a crucial supporting role in pre-disaster assessment of the risk level of debris flow and post-disaster auxiliary evaluation of the severity of debris flow.
[Objective]Baseflow is a relatively stable component of runoff.Accurately characterizing the spatiotemporal distribution characteristics of baseflow in river basins,especially its response to vegetation variations,is crucial for water resource and river basin management in the water-scarce mountainous areas of northern China.[Methods]The SWAT model was coupled with the numerical simulation-based ensemble baseflow separation technique.Taking the Xiaoluan River Basin as an example,the spatiotemporal variations of baseflow in the study area were analyzed,and the controlling effect of vegetation variations on river basin baseflow were investigated.[Results]The result showed that:(1)the coupled application of the SWAT model and the ensemble baseflow separation technique could effectively simulate the hydrological processes in areas with limited baseflow.The baseflow simulation performed well,with a coefficient of determination as high as 0.9,demonstrating strong applicability of this method.(2)From 2006 to 2020,the annual and growing-season runoff and baseflow in the Xiaoluan River Basin showed an overall decreasing trend,although the trend was not significant.In contrast,the runoff and baseflow during the non-growing season increased significantly(p<0.05).(3)During the study period,baseflow remained generally stable in approximately 35.85%of the river basin area,with distribution across the upper,middle,and lower reaches.In the mountainous area near the dam,baseflow in some sub-basins even showed a significant increase(accounting for 22.47%of the river basin area).In contrast,in the alpine meadow area above the dam,baseflow showed a slight decrease(accounting for 18.32%of the river basin area)or a significant declining trend(accounting for 19.82%of the total area).(4)Vegetation was one of the important influencing factors for the improvement of baseflow processes in the study basin.In most parts of the mountainous area near the dam,NDVI and baseflow showed a positive correlation,and some sub-basins even showed a significant positive correlation(accounting for 10.68%of the total river basin),indicating that vegetation restoration was conducive to the improvement of baseflow processes in the study area to a certain extent.[Conclusion]At present,the increase in vegetation cover in the study area has a certain positive controlling effect on baseflow process.However,due to the interaction of processes such as spring snowmelt recharge,the controlling effect of vegetation on baseflow under future climate change requires continuous observation and investigation.
[Objective]Global climate change,population growth,and intensified social activities have led to variations in the spatiotemporal distribution of water resources,posing challenges to the development and utilization of water resources.Optimizing the water scheduling of cascade reservoir groups is crucial for water resource allocation.However,current research lacks sufficient consideration of decision-makers' preferences for water shortage patterns and time.[Methods]To address the challenges in water resource allocation,an optimal water volume scheduling model for cascade reservoir groups was established with the primary objective of minimizing water supply deficits.Three water shortage pattern strategies—total water supply deficit control,centralized distribution,and wide-shallow distribution—were proposed,along with water shortage time strategies that adjusted weights across different periods.Then,an analysis was conducted using the Toutun River Basin as a case study.[Results]In the case study of water shortage pattern strategies,when the inflow frequency was p=50％,the wide-shallow distribution pattern result ed in the smallest supply deficit(493 700 m3),the centralized distribution pattern result ed in the largest deficit(1 797 400 m3),and the total water supply deficit control pattern fell in between(973 300 m3).When the inflow frequencies were p=95％and p=75％,although the total supply deficits under the three patterns were similar,the water shortage was more evenly distributed under the wide-shallow distribution pattern.In the analysis of the water shortage time strategy,using p=95％as an example,after applying the strategy,the water supply deficits in March to May decreased from 58 400 m3,5 735 800 m3,and 6 246 600 m3 to 49 000 m3,134 000 m3,and 124 600 m3,respectively.However,the deficits in other months increased from 32 496 200 m3 to 44 223 200 m3,and the total water supply deficit remained essentially unchanged.[Conclusion]In summary,the proposed strategies are proven effective.The wide-shallow distribution pattern demonstrates clear advantages in ensuring supply stability.The water shortage time strategy can reduce water supply deficits in specific periods,but it does not reduce the total deficit—it only redistributes the time of the shortage.The findings can serve as a reference for water allocation of cascade reservoir groups.
[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.
