Analysis Of Spatial-temporal Distribution Of Precipitation-induced Loess Landslide Hazards And Crucial Factors In Lanzhou

Lanzhou is a typical valley city,located in western China.With the special landforms of "one river sandwiched between two mountains",the area has complex geological structures,extremely developed folds and faults,various types of loess,and distinct cut-layer characteristics.Landslides can easily happen under the conditions of rainfall.Because of abrupt,widespread,and catastrophic nature of loess landslide disasters,the life and property safety of residents,factories,and roads which near the mountains are severely affected,and urban construction and economic development are constrained.Statistical analysis finds that,as the primary factor of loess landslides,rainfall induces about 85.6% of landslide disasters in Lanzhou.Spatial-temporal distribution of precipitation-induced loess landslide hazards and its crucial factors can provide fundamental basis for disaster prevention and mitigation.In this paper,the long-span landslide data is taken as the research object for the first time,and rainfall is used as a key factor to conduct a long-term analysis of historical landslides and rainfall data in the study area to study its spatial-temporal changes.In order to effectively improve the accuracy of rainfall landslide warning and provide methods and data references for solving problems of landslide hazards such as susceptibility assessment and early warning.Based on daily precipitation data,distribution and historical events of loess landslide data from 1965 to 2015 of Lanzhou,this paper analyzed precipitation-induced loess landslide and rainfall for different categories including rain days,precipitation and precipitation contribution rate,in order to get its spatial distribution characteristics.Mann-Kendall test,moving t-test and Morlet wavelet transformation were used in the study.The paper also discussed the correlation between landslides and its key hazards,such as rainfall,formation lithology and slope.The main conclusions are as follows:(1)The rainfall events in Lanzhou City are characterized by light drizzle,light rain and moderate rain.In the past 50 years,the rainfall and the number of rainfall days are all abrupt,and the mutation time is different and most mutations are detected by the ?=0.05 significance test.There are obvious multi-time-scale periodic oscillations of rainfall,and the variation period of the number of rainfall days is mainly 8a.(2)Rainfall differs greatly in spatial distribution,the number of annual rainfall days showed "two more and two less",and precipitation showed "two less and two more",and the degree of rain events of different grades has different impacts on rainfall in different areas.(3)Precipitation-induced loess landslides frequently happened from April to October.The overall distribution of landslides is uneven,regional feature of density is "two highs and two lows".The kernel density estimation(KDE)analysis shows that the landslides are locally concentrated,and the density in Chengguan district is high and forms a circular distribution.The density in Xigu district gradually reduces from east to west and forms a banding distribution.(4)Rainfall is the main reason for inducing loess landslides in the study area.In temporal distribution,the abrupt point and main variation period of rainfall are consistent with the high incidence of landslides.In spatial distribution,the number of loess landslides have a certain correlation with rainfall days and precipitation.