| Debris flow is one of the most serious geological disasters in the Qinghai-Tibet Plateau and its surrounding areas.The loose accumulation caused by a large number of landslides within the channel is an important source of debris flow.The spatiotemporal variation of landslides determines the number and distribution of loose sources to a certain extent,and further affects the frequency and intensity of debris flow.Clarifying the spatiotemporal evolution characteristics of landslides at the valley scale and their influence on debris flow activities is of great significance for regional hazard prevention and mitigation.However,most of the existing studies focus on the spatial distribution of regional landslides,and mainly describe the spatial characteristics of landslides under specific induced events(such as earthquake and rainfall,etc.).There is a lack of discussion on the spatiotemporal change rule and mechanism of landslides,and even less correlation between the spatiotemporal evolution of landslides and debris flow activity.Therefore,understanding the characteristics and mechanism of landslide spatiotemporal evolution and its impact on debris flow activities are the key problems that need to be solved urgently in the field of geological disaster management in the Qinghai-Tibet Plateau and surrounding areas.The Bailong River Basin,located in the eastern margin of Qinghai-Tibet Plateau,is a high-risk area for geological disasters in China.In recent years,influenced by earthquakes,extreme rainfall,and human engineering activities,landslide,debris flow,and other geological disaster activities have further increased,with the chain effect being significant.Especially after the Wenchuan earthquake,the strong disturbance has made the area become the most severe secondary geological hazard-prone area except for Sichuan Province,and there are obvious postseismic effect.In addition,due to the high mountains and steep slopes and deep valleys in this region,human activities are mainly concentrated in the relatively flat river valley area.With the development of national urbanization,engineering construction has continuously expanded to both sides of the river valley,further affecting the development and evolution of geological disasters such as landslides and debris flows,resulting in differentiated disaster-prone environments in different sub-basins.Therefore,this study selected the Goulinping and the Ganjiagou,two disaster-prone valleys with different human engineering disturbances in the Bailong River Basin,for comparative study.With the help of satellite optical remote sensing,unmanned aerial vehicles,In SAR(Interferometric Synthetic Aperture Radar,In SAR)technology and field investigation,the spatiotemporal distribution law and activity change of landslides were revealed,and the driving mechanism of spatiotemporal evolution of landslides was explored by combining machine learning.Based on the evaluation model of landslide sediment supply capacity,the influence of landslide on debris flow activity was clarified,and the potential source amount provided by slope material to debris flow was quantitatively evaluated.The main research results obtained are as follows:(1)The spatiotemporal evolution of landslides is revealed through the multitemporal landslide cataloging.The results showed that the number of landslides in the study area increased significantly in the past 15 years,with the largest increase after the Wenchuan earthquake in 2008 and the extreme rainfall event in 2020.Human engineering increased the frequency of small landslides.Different types of landslide have different distributions.The slides are mainly developed in soft rock area,the falls are mainly developed in steep slope or hard rock area,and the flows are mainly developed in concave slope.Coseismic landslides often occur at high altitudes and steep slopes,while extreme rainfall events often trigger landslides in soft rocks,concave slopes and human disturbed areas.(2)Landslide activity was obtained by combining In SAR technology and optical images.The change trend of landslide activity in the study area in recent 15 years shows as follows: before the Wenchuan earthquake,the landslide activity was relatively low;After the Wenchuan earthquake,the proportion of active landslide reached about 90%,and the activity of landslides in high altitude area increased more significantly.From2017 to 2019,the proportion of active landslide decreased to 45%;After the occurrence of extreme rainfall events in 2020,the proportion of active landslides increased to about80%,and a large number of new active landslides occurred in soft rock areas.Most large landslides with human engineering are in active state for a long time,and small active landslides are often developed in densely populated areas with human engineering.(3)The dynamic changes of the main controlling factors of landslide spatiotemporal evolution were determined based on machine learning.The Wenchuan earthquake has a strong control effect on the landslide activity in the area,and has obvious terrain amplification effect.The postseismic effect has lasted for nearly 10 years in the area,and the external driving factors have the conversion mode of rainfall and earthquake.The concave slope with low lithology intensity is sensitive to rainfall,and the possibility of landslide is higher in the future climate scenario.In addition,human activities can reduce the threshold of triggering landslides under the same conditions and increase the risk of slope landslide.(4)Determine the influence of landslide on debris flow activity based on statistical model.The scale or frequency of debris flow in the study area increases when the potential source quantity is large or the increase is large.After the Wenchuan earthquake,the landslide sediment supply capacity increased by 50%,the potential source volume increased by nearly 2 times,and debris flow activity increased and lasted for nearly 5years.After extreme rainfall events,shallow landslides in adjacent gully can quickly provide source and increase the scale of debris flow.Human engineering can change the transport process of loose materials.The results of this study reveal the spatiotemporal variation and development law and driving mechanism of landslides driven by multiple factors,and clarify the influence of spatiotemporal evolution of landslides on debris flow activity,which improves the theory of landslide disaster in the eastern margin of Qinghai-Tibet Plateau to a certain extent,and can also provide scientific basis for geological disaster prediction and risk management in the Bailong River Basin and similar areas. |
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