| The ecological geological environment(eco-geo-environment)is an open dynamic system.The interaction coupling relationship and synergy mechanism of each subsystem have an impact and control effect on various environmental problems and disasters faced by human beings.In recent years,global climate change has led to an increase in extreme precipitation events in regions,coupled with the continued enhancement of human activities,leading to an increasing frequency of debris flow disasters in mountainous areas of China,causing significant losses and threats to the lives and properties of local people,important facilities,and socio-economic development.Comprehensive prevention and control of debris flow have become an urgent need for ecological security construction in China.However,existing studies at home and abroad have not yet clarified the coupling and synergistic mechanism of the eco-geo-environment at the watershed scale in mountainous areas,as well as the role and contribution of climate change and human activities in the distribution.In particular,in the context of climate change,there is a lack of in-depth understanding of the impact and role of strong human activities such as check dams for debris flow mitigation and ecological prevention measures on debris flow disasters and in-depth research is urgently needed.Therefore,this paper takes the Bailong River Basin(BRB),located in the high mountain gorge on the eastern edge of the Qinghai-Tibet Plateau,where geological disasters are extremely serious,as the research area.Through the study of the coupling and coordination mechanism of the eco-geo-environment system at the watershed scale,the risk assessment and prediction of debris flow at the watershed scale have been carried out;And the Goulinping,Ganjiagou,and Sanyanyu debris flow gullies in the Bailong River mainstream,which have implemented different prevention and control measures(untreated,comprehensive treatment,and geotechnical engineering treatment),are selected as typical debris flow gullies.The impact and contribution of ecological engineering and geotechnical engineering on debris flow hazard risk under of shared socioeconomic pathways(SSPs)and representative concentration pathways(RCPs)(SSP-RCP)scenarios(SSP1-2.6,SSP2-4.5,and SSP5-8.5)were analyzed by comprehensive use of SWAT and BASEMENT models.The main research conclusions are as follows:(1)Analysis of spatial distribution characteristics of debris flow hazards in BRBThe development of debris flows in the BRB has significant spatial heterogeneity under the combined effects of eco-geo-environmental factors such as geology,climate,hydrology,soil,and vegetation.The frequency of debris flow occurrence in about 55%of gullies in the basin was greater than 2 times per year.From the perspective of the county level,the average frequency of debris flows in Wudu District was the highest,at 5.65 times per year,with the frequency of debris flows in some gullies on both sides of the Beiyu River even exceeding 10 times per year.Through spatial correlation analysis,regions with high frequency and high concentration of debris flows were concentrated on both sides of the Bailong River in the Wudu-Wen County section and on both sides of the Beiyu River in the Wudu District.(2)Coupling mechanism of the eco-geo-environment system and its impact on debris flow disaster in BRBBased on the analysis and prediction of the spatiotemporal variation characteristics of the key factors of the eco-geo-environment in the basin,this paper applied the projection pursuit model to determine the index weight and quantitatively evaluated the comprehensive quality level of the three subsystems of the ecological,geological,and human environment in the BRB.And revealed the coupling mechanism between the eco-geo-environment subsystems.The interaction between the factor sets of the geological environment,ecological environment,and human environment subsystems can explain a total of 86.9% of the changes in the frequency of debris flow.The distribution of debris flow disasters was most affected by geological environmental factors.The cluster area with the highest frequency of debris flow disasters(4times/year)is the absolute advantage of human environmental subsystem,and the quality level of ecological and geological environmental systems is low.(3)Risk assessment and prediction of debris flow hazards on a basin scaleThis article takes the BRB as an example,based on the eco-geo-environment system factors,and used machine learning algorithms and contribution weight superposition method to carry out debris flow risk assessment and prediction.The highrisk areas of debris flow disasters were mainly distributed in the northern part of Wudu District and Tanchang County,which were areas with relatively intensive economic activities and high disaster frequency.The BCC-CSM2-MR model data in the CMIP6 climate model was selected and the future debris flow risk in the BRB was calculated under three SSP-RCP scenarios of this model.And combined with future socioeconomic development path data,the vulnerability of disaster-bearing bodies in different periods of the BRB was calculated.On this basis,the risk of debris flow disasters in the BRB from 2040 to 2100 was predicted.Among them,under the SSP1-2.6 and SSP2-4.5 scenarios,the risk of debris flow disasters showed a decreasing trend from 2040 to 2100.Under the SSP5-8.5 scenario,the risk of debris flow disasters was the highest and showed a significant increasing trend.(4)Risk assessment of debris flow hazards in the typical small watershed of debris flow gullies under different control measuresBased on the parameter adjustment results of SWAT and BASEMENT models,a debris flow risk assessment was conducted for typical debris flow gullies(Goulinping,Ganjiagou,and Sanyanyu)in the BRB.The high-risk in Goulinping was mainly medium to low,and the high-risk area only accounted for 13.01% of the total area,mainly located in residential areas and highway areas at the mouth of the ditch.In real scenarios(with check dams)in the Ganjiagou watershed,the main risk areas were medium to low risks,with high-risk areas accounting for 13.24% of the total area.In real scenarios(with check dams),the debris flow risk in Sanyanyu was mainly medium to low,with high-risk areas accounting for only 11.93% of the total area.(5)Risk prediction of debris flow disasters in the typical small watershed of debris flow gullies under different control measuresBased on data from three scenarios(SSP1-2.6,SSP2-4.5,and SSP5-8.5)from2040 to 2100,different scenarios were set up to predict the risk of debris flow disasters based on the implemented prevention and control measures for three typical debris flows.In the Goulinping watershed,the risk of debris flow disasters showed a decreasing trend under the SSP1-2.6 and SSP2-4.5 scenarios,while the SSP5-8.5 scenario was the opposite.Among them,climate change was conducive to increasing the risk of debris flow disasters in Goulinping.The SSP1-2.6 land use scenario was conducive to reducing the risk of debris flow disasters,while the SSP2-4.5 and SSP5-8.5 land use scenarios were conducive to increasing risk.In the Ganjiagou watershed,The risk prevention and control effect of debris flow disasters: comprehensive control measures>check dams>vegetation measures in gullies.The debris flow control measures were most effective in the SSP1-2.6 scenario,followed by the SSP2-4.5scenario,and finally the SSP5-8.5 scenario.It indicated that both check dams and vegetation measures in gullies can effectively reduce the risk-promoting effect of climate change on debris flows.In the Sanyanyu watershed,Under the SSP1-2.6 scenario,the risk of debris flow decreased over time,while the SSP2-4.5 and SSP5-8.5 scenarios were the opposite.Compared with the scenario without check dams,the high-risk area decreased by approximately 89.04%,68.27%,and 72.15% under the three scenarios with check dams,respectively.In summary,the above research conclusions deeply reveal the coupling and synergistic mechanism of ecological,geological,and environmental factors in the BRB,a high incidence area of debris flow disasters,and analyzing their roles and contributions to the risk of debris flow disasters.The research results can provide scientific basis and technical support for carrying out ecological engineering prevention and control of debris flow disasters in the high-risk areas of debris flow disasters in western China and building a comprehensive prevention and control system,and makeing due contributions to improving China’s ability to prevent and reduce disasters. |
