| The geological and ecological environment of loess area in China is fragile.Due to the impact of global climate change,the frequency of extreme rainfall is increasing,which makes the loess landslide disasters occur frequently in recent years.Tianshui is located in the southeast of Gansu Province,has been suffering from landslides since ancient times.The frequent landslides have seriously threatened the safety of local people's lives and property,and restricted the development of the city.Using the technical means to carry out landslide hazard early warning,which can make disaster emergency and prevention departments work out related prevention measures in advance.In this paper,historical landslides in Tianshui were taken as the research object.The rainfall model and the landslide sensitivity model were constructed respectively,and the comprehensive hazard warning model of rainfall-type landslides was obtained by coupling the results of the two models,so as to realize the regional rainfall-type landslide risk warning and provide theoretical basis for disaster warning and prevention.The main research contents and achievements are as follows:(1)The historical rainfall-induced landslide data of Tianshui City,Gansu Province were collected and analyzed.It was found that the number of landslides was basically consistent with the variation of annual,monthly and daily rainfall,and the occurrence of landslides had a certain lag.There was a fractal relationship between the cumulative rainfall in the early period of landslides and the days of rainfall in the early period.The effective rainfall days for triggering landslides in Tianshui City were 7 days.The temporal and spatial distribution of rainfall critical value in Tianshui city based on the early effective rainfall was obtained by constructing the model of early effective rainfall.The previous effective accumulated rainfall of 30 mm,40mm,50 mm and60mm was used as the basis for the classification of rainfall threshold hazard.It has been proved that the threshold determination of the early effective rainfall model and the classification of rainfall threshold risk grade are reasonable.(2)Based on Arc GIS software platform,the internal and external factors that trigger landslide events are analyzed.Eleven influencing factors were extracted,including elevation,slope,aspect,topographic relief,profile curvature,topographic wetness index,stratigraphic lithology,soil type,vegetation coverage,land use type and distance from river.Based on the decision tree model,the importance and weight of geological factors and environmental factors of landslide induced were sorted and assigned.And the information content model is used to realize the landslide susceptibility regionalization in Tianshui area of Gansu Province.The ROC curve was used to test the subdivision,and the AUC value was 0.824,indicating that the model obtained by the susceptibility subdivision after weighting the landslide impact factors based on the decision tree had a well accuracy.(3)According to the existing threshold index of rainfall-induced landslide and related standards in Tianshui,the comprehensive hazard warning model of rainfall-type landslide in Tianshui was established by coupling the effective rainfall and the landslide susceptibility model in the early stage.And based on the decision matrix,the risk warning levels of rainfall-induced landslides were divided into five levels: lower hazard(?),low hazard(?),medium hazard(?),high risk(?)and higher risk(?).The model was verified by the landslide in Taijing town of Qinzhou district in August 2020,and the warning results are basically consistent with the actual situation,which indicates that the model is suitable for the comprehensive hazard warning of raininduced landslides in Tianshui.Based on the warning level of the constructed landslide comprehensive hazard warning model,combined with the particularity of loess formation mechanism,on the basis of absorbing and drawing lessons from the existing prevention and control methods,the corresponding treatment suggestions and measures for different levels of dangerous landslides in the loess area of Tianshui were put forward. |
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