| The frequency of intense rainfall events has increased as a result of global climate change.Due to the unique structure and water sensitivity of loess,the Loess Plateau is prone to soil and water hazards,such as landslides and debris flows.However,despite the ability of many academics to forecast the geographic location of landslide occurrence through regional stability modeling,further research is required on the mechanism of initiation and secondary hazard evolution of cluster loess landslides under heavy rainfall.To address this gap,we simulated regional stability using the slope stability analysis model embedded in TRIGRS and the stability calculation model embedded in Open LISEM.Specifically,we used the disaster event that occurred in the central area of Ma Runquan Town,Tianshui City,from July 20,2013,at 0 hours,to July 22,2013,at 8 hours,to compare the results and determine the best calculation method.Furthermore,we simulated the motion of ensuing secondary debris flow risks using the mixed motion model of solid and liquid phases,which is integrated into Open LISEM.To validate the accuracy of our model and calibrate its parameters,we used real-world data on hazard distribution.We then examined the distribution pattern of soil and water hazards in the research region under various geomorphological and extreme precipitation situations.Here are the key findings of our study:(1)Using the central area of Ma Runquan Town as the study site,we analyzed regional stability using stability calculation models embedded in Open LISEM and TRIGRS.The results were compared with the actual distribution of disasters in the area.Our findings indicate that both TRIGRS and Open LISEM were effective in fitting stability calculations in loess environments after extreme precipitation,with %LRclass indices of 84.18% and 84.72%,respectively.However,TRIGRS outperformed Open LISEM in reflecting stability changes before and after rainfall,with unstable areas accounting for 1.66% and 11.27% before and after rainfall,respectively.(2)In the subsequent debris flow evolution simulation,the maximum height,velocity,and deposit height of the debris flow were 15.5 m,13.0 m/s,and 13.5 m,respectively.The danger level of the disaster was evaluated based on the relationship between the disaster scope and the location of residential areas.The results showed that although only one residential area contained unstable areas after the extreme rainfall from July 20,2013,0:00 to July 22,2013,8:00,there were 12 residential areas within the movement range of subsequent debris flow,indicating that using the stability model of TRIGRS and the two-phase motion model of Open LISEM in combination can more comprehensively estimate the danger of the study area.(3)In this study,we simulated the regional stability and subsequent debris flow evolution in the central area of Ma Runquan Town under two different rainfall scenarios: short-duration heavy rain and continuous light rain.We used the aforementioned optimal calculation methods.Results showed that under the short-duration heavy rain scenario,as the rainfall intensity increased,the proportion of unstable areas increased from 1.71% to 15.95%,the number of safe areas for residents decreased from 18 to 7,and the magnitude of disasters continuously increased.Under the continuous light rain scenario,as the rainfall duration increased,the proportion of unstable areas increased from 3.97% to 9.96%,the number of safe areas for residents decreased from 17 to 10,and the magnitude of disasters continuously decreased.When the cumulative rainfall was the same,the proportion of unstable areas triggered by short-duration heavy rain and the number of debris flow-affected bodies were both greater than those in the continuous light rain scenario.(4)The eastern part of Ma Runquan Town,which features a distinctive valley terrain structure compared to the three-sided mountain terrain structure in the central area,was selected as the research subject for simulations conducted under different terrain scenarios.Short-duration heavy rain and continuous light rain were used as rainfall scenarios,and the aforementioned optimal calculation methods were applied to simulate the regional stability and subsequent debris flow evolution in the eastern part of the town.The results indicated that under the short-duration heavy rain scenario,the proportion of unstable areas increased from 0.5% to 15.55%,and the number of safe areas for residents decreased from 23 to 12 as the rainfall intensity rose.Both unstable and affected areas expanded rapidly in the valley and mountain terrains,with their instability and failure slopes concentrating in the range of 12-30°.As the rainfall intensity increased,more lower slopes transformed into unstable areas,providing more material sources for subsequent debris flow evolution.Under the continuous light rain scenario,the proportion of unstable areas increased from 0.88%to 1.87% as the rainfall duration increased,and the number of safe areas for residents declined from 22 to 19.No significant change in disaster magnitude was observed in the valley terrain study area.The research findings contribute to the risk prediction of mass disasters in loess areas,enabling early prevention and reinforcement of potentially affected areas,thereby reducing the threat to residents’ lives and property. |
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