| Rainfall is the most important and changeable index of risk assessment of debris flow,it is very important for evaluating the accuracy of debris flow risk assessment.The risk assessment of debris flow based on the relationship between debris flow and rainfall can provide scientific basis for the prediction of debris flow disasters.This study takes the Panxi area of Sichuan Province as a typical case area,1971-2016 years of rainfall data and 1949-2016 years of actual debris flow data are used,Mann-Kendall method and Precipitation concentration degree were used to study the distribution regularities and formation conditions of the debris flow disaster and rainfall in Panxi.The rainfall index of debris flow hazard assessment is selected by the correlation analysis and the geographic detector model based on the analysis of the relationship between debris flow and rainfall.The risk assessment of debris flow is carried out by using the contribution weight model and the deterministic weight model based on certainty factor.The accuracy of the evaluation results is verified by the frequency ratio model combined with the actual debris flow point,which provides the basis for disaster prevention and mitigation in Panxi area.The main research results were as follows:(1)The yearly precipitation,the annual storm rainfall,the annual heavy rainfall were decreased,while the annual mid-rainfall showed an upward trend in the study area in the study area from 1971-2016.The rainfall in the year is mainly concentrated in June-September.The high value center of the average annual rainfall is located on the Ganluo-Huili,the second high value center is the Leibo-Ningnan-Huidong,and the low value center is the Muli-Yanyuan-Panzhihua.The average annual rain frequency is decreasing from northeast to southwest.The distribution of rainstorm in terms of amount and frequency in southwest is more than that in northwest.The distribution of heavy rain in terms of amount and frequency is less in the northwest,more in the middle and south.The distribution of moderate rain in terms of amount and frequency is heavy in the north part of the study area.(2)Debris flow disasters and rainfall in the study area have a good correlation in spatio-temporal distribution.In particular,the spatial distribution of debris flow disasters is closely related to rainfall,rainstorm frequency and heavy rain in flood season.The study on the relationship between debris flow and short-term rainfall amount showed that Debris flow may occur,when the rainfall intensity reached 16mm/h and above,and 12h rainfall reached more than 20mm,the daily rainfall exceeds 50mm in Panxi area.The relationship between debris flow and pre-rainfall study found that debris flow can be divided into heavy rain debris flow,continuous heavy rain debris flow,and early rainfall debris flow.(3)Slope,distance from faults,distance from rivers,comprehensive index of rainfall,and land use have a greater weight in the risk assessment of debris flow.The formation conditions of debris flow are as follows:elevation is less than 2km;slope is less than 40°;chonostratigraphy is Quaternary,Mesozoic,Lower Proterozoic;aspect is NE,SW,E,S;distance from faults,roads,and rivers are less than 2km,the peak ground acceleration is greater than or equal to 0.2g,the comprehensive rainfall index is in the range of 0.485-0.661,and the type of land use is cultivated land,construction land and unused land.(4)The evaluation precision of the weighted model based on the certainty factor method is higher than that of the contribution weight model.The total number of actual debris flows included in the middle,high,and extremely high risk areas of the evaluation results of the two models respectively account for 92.56%and 72.65 of the total number of inspection debris flows.The extremely high-risk and high-risk areas are distributed along both sides of the fault in the central,southern and eastern parts of Panxi and along the Yalong River,Jinsha River and its tributaries. |
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