Driving Factor Analysis And Risk Assessment Of Flash Flood Disaster At Different Spatial Scales In Guanzhong Area

In the history of our country,flash flood disasters mainly caused agricultural losses.With the continuous development of China’s economy and society,the losses caused by flash flood disasters have begun to shift to cities.Due to the relative concentration of population and assets in cities,the losses caused by flash flood disasters are much larger than those in rural areas.At the same time,due to its destructiveness,wide range and fast speed,it is difficult for people to forecast flash flood disasters and post-disaster reconstruction.Therefore,it is an important work to carry out mountain flood disaster prevention and control.The Guanzhong area includes five prefecture-level cities:Xi ’an,Xianyang,Tongchuan,Baoji and Weinan.Its population accounts for about 60%of the total population of Shaanxi Province,and its economic aggregate exceeds 60%of Shaanxi Province.Once a flash flood disaster occurs,it will be very destructive and the loss will be very serious.Therefore,this study first analyzes the distribution characteristics of flash flood disasters from two scales of time and space.Then,from the three different scales of town,small watershed and grid,the driving effect of each influencing factor on the occurrence of flash flood disaster is revealed.Finally,based on the results of driving force detection,the risk assessment of mountain flood disaster in Guanzhong area is realized based on the combination weighting method.This study has a certain guiding role in the prevention and control of flash flood disasters in Guanzhong,and helps to improve the comprehensive defense level of flash flood disasters.The main research contents and results are as follows:(1)Study on the temporal and spatial characteristics of flash flood disasters.The data of flash flood disasters in Guanzhong area from 1949 to 2015 were collected,and the temporal and spatial characteristics of flash flood disasters in Guanzhong area were analyzed from two scales of time and space.The results show that the flash flood disasters in Guanzhong area are mainly concentrated from July to September in the intra-annual distribution of time scale,and the interannual distribution of flash flood disasters in Guanzhong area increases by time period.At the same time,the periodic variation has multi-scale characteristics,which is mainly manifested in the strongest periodic oscillation in 12 years.From the spatial scale,the flash flood disasters in Guanzhong area tend to be agglomerated and unevenly distributed,mainly concentrated in Baoji City,Xianyang City and Weinan City.On the whole,the spatial distribution pattern of ’southwestnortheast dispersion,northwest-southeast aggregation’ is presented.(2)Study on the driving force of flash flood disaster at different spatial scales.Eleven index factors such as rainfall factor,underlying surface factor and human activity factor were selected,and the driving forces of index factors in Guanzhong area were analyzed from town scale,small watershed scale and grid scale by using geographic detector and random forest model.The results show that the geographical detector P(10-25)has the greatest impact on the flash flood disaster in Guanzhong area from the town scale,and the small watershed scale and grid scale are DEM;the random forest model has the greatest impact on the flash flood disaster in Guanzhong area from the town scale is P(25-50),and the small watershed and grid scale is P(50-100);the importance ranking of the driving factors of flash flood disasters in Guanzhong area by geographical detector and random forest model is different,among which the ranking difference of town scale is the largest and the grid scale is the smallest.(3)Combination weighting mountain flood disaster risk assessment.Based on the results of the geographic detector and the random forest model,the entropy weight method and the analytic hierarchy process are used to calculate the weights respectively,and the combined weights are calculated by the game theory.Finally,ArcGIS is used to evaluate the risk in Guanzhong area.The results show that the possibility of flash flood disasters in Guanzhong area is high.Among them,the area of high risk area of flash flood disasters in Guanzhong area is the largest,which is 17968.10 km2,accounting for more than 30%.From the characteristics of different attribute data,it can be seen that the main reason for flash flood disasters in high-risk and high-risk areas is that the number of precipitation in the region is generally more and the intensity is large,the socioeconomic development,urbanization rate is high,the population is large,the vegetation coverage rate is low,and the loss of flash flood disaster is large.