Study On Risk Assessment And Risk Management Of Flood Disaster Based On Cloud Model

Flood disasters have always existed along with the historical process of human beings and have become an important threat to human survival and development.Flood risk assessment can help people understand the probability and distribution of losses caused by floods,and provide a theoretical basis for the formulation of relevant disaster prevention and mitigation policies.However,flood risk assessment is a complex system involving more assessment factors and more complicated evaluation process.Some qualitative assessment factors maybe encounter some quantification problems.New theoretical methods are needed to optimize and improve.Chaohu Basin is a region with high flood disasters in history.Now it is the core area of the Wanjiang City Belt approved by the State Council for the establishment.It is urgent to study the distribution of flood disasters in the basin and propose targeted disaster prevention and response measures.This paper starts with the flood risk assessment process and combines theoretical analysis with computer simulation,and uses ArcGIS,Matlab and data analysis software to conduct comprehensive assessment and management of flood disaster risk in Chaohu Basin.In view of the randomness and ambiguity of the assessment index data in the flood risk assessment process,this study introduces a qualitative and quantitative transformation model based on stochastic mathematics and fuzzy mathematics--the cloud model theory,which exerts its advantages in expressing the uncertainty of things and quickly solving the problem of qualitative and quantitative data conversion.It improves and optimizes the risk assessment of flood disasters,and establishes a comprehensive assessment model of regional flood disaster risk assessment based on cloud model theory.Mainly reflected in the following three aspects:(1)The qualitative and quantitative conversion methods in flood risk assessment often ignore the uncertainty of the qualitative concept itself,and directly use the "Solid" boundary to divide the assessment interval,which is easy to produce errors.This study extends the one-dimensional cloud model to two-dimensional and multi-dimensional cloud models.By constructing conditional clouds,comment clouds and cloud reasoning rules,the terrain risk assessment algorithm is improved,and the boundary of the qualitative concept in the original method is softened.It overcomes the deficiency in ability to reflect the ambiguity and randomness,and provides new methods and approaches for the assessment of multiple factors of flood risk.Topographic hazard analysis shows that Hexian,Wuwei Counties and Chaohu City which located in the alluvial plains,are affected by the floods of the Yangtze River and Chaohu Lake in flood season,and the risk is the highest;Hefei City,the southeastern part of Feixi County,the eastern part of Shucheng County and Lujiang County are located between the low hills and the alluvial plain.The terrain has certain ups and downs and the risk is second highest.The Feidong County,the central part of Shucheng County and most of Feixi County are low hills.The average elevation of the area is about 50m.The terrain is obviously undulating and the risk is moderate.The southwest of Shucheng County that is located in Dabie Mountains and some mountainous areas in Chaohu City and Hanshan County have an average elevation of over 400m.The terrain changes greatly and the terrain risk is relatively low.(2)The local area precipitation history usually exhibits a quasi-periodic law and also has a certain sustained stability.In this study,the cloud model theory is introduced into the precipitation simulation prediction research.The maximum entropy spectrum analysis method is used to obtain the precipitation quasi-period,and the cloud model method is used to generate the historical cloud and the trend cloud and establish a regular cloud precipitation prediction model to obtain a better prediction effect.It also provides a new research method to the precipitation indicator prediction of disaster risk.The research shows that,except for some errors of Feixi,Wuwei and Hanshan simulation values,the precipitation simulation values generated by other cities and counties according to the regular cloud are consistent with the actual precipitation.The simulation errors are all around 10%,and the average error is 14.43%.It is better than the results in BP neural network.From the distribution of regular cloud generation results,the expected precipitation values of Lujiang,Wuwei and Hexian in the south and southeast of the basin are higher,indicating that their precipitation may be higher than others in the future.At the same time,the cloud entropy of Wuwei,Chaohu and Feixi counties is higher,indicating that the precipitation in these areas is more uncertain,and the possibility of large precipitation in the flood season is relatively high.(3)Analytic Hierarchy Process is the main method for establishing the weight of indicators in flood disaster risk assessment models,but it cannot reflect the ambiguity and randomness of the objective world.Based on the analytic hierarchy process,this paper constructs a cloud-model improved flood risk assessment index system(Cloud-AHP),replaces the original digital scale with cloud scale,and establishes a cloud judgment matrix for analysis.It not only contains the uncertainty of the objective world reasonably,but also can quickly and effectively aggregate the decision-making judgments of many experts,making the determination of the weight of the flood disaster risk indicator system more objective and accurate.Under the framework of the flood disaster risk index model,nearly 50 risk assessment indicators in the flood risk assessment literature at home and abroad are summarized.Using the Delphi method and combining the actual situation of the Chaohu Basin,21 assessment indicators for precipitation,topography,water system,economy,population and land from hazard,exposure and vulnerability categories were seleted.The cloud judgment matrix and importance cloud vector of each level were calculated respectively by using Cloud-AHP method.After passing the consistency test and obtaining the weight of each indicator,the modeling of the flood disaster risk system is completed.Using GIS spatial analysis tools to analyze and overlay all the indicator maps of flood disasters in Chaohu Basin,the flood risk distribution map of Chaohu Basin is obtained.In general,the high-risk areas show a left-half enveloping situation,which is roughly in the shape of the capital letter "C",that is,the risk in the northern,western and southern parts of the basin surrounding the lake is relatively high,while the area east of Chaohu Lake and the Dabie Mountains region in the southwest of the basin are less risky.Specifically,the central and southern parts of Wuwei County,and the southern part of Lujiang County which are adjacent to the Yangtze River,are the areas with the highest risk in the whole river basin;the southern part of Feixi County in the north of the basin and the Baohe District in Hefei City have higher exposure and vulnerability,and also belong to higher risk areas;the central and northern parts of Shucheng County,the northern part of Lujiang County,the western part of Feidong County,and most of Feixi County are at medium-risk levels;the southwest of Shucheng County and the mountainou areas of Chaohu City and Hanshan County have a relatively low-risk level.Finally,according to the results of flood risk assessment in Chaohu Basin,12 counties in the basin are divided into high,medium and low risk levels,and management strategies are proposed based on the risk level and actual situation.For the high-risk areas of Wuwei County,Lujiang County along the Yangtze River,Feixi County,Baohe District of Hefei City in the north,it is recommended to play the role of disaster risk zoning,strengthen the remediation and management of small and medium-sized rivers,promote the compliance of large and medium-sized reservoirs and exert their ability to regulate floods,establish disaster monitoring and alert service systems to strengthen flood forecasting and warning work.For the middle-risk areas such as Shucheng County,Feidong County,Chaohu City,Shushan District and Hexian County,it is recommended to focus on strengthening emergency response capability,improve the flood emergency management system,and increase the publicity and education of flood disasters.For low-risk areas such as Yuyang District and Yaohai District of Hefei City and Hefei City,it is necessary to focus on improving the town's ability to prevent infighting,paying attention to the protection of ecological environment while constructing flood control facilities,and strengthening the comprehensive monitoring of flood disasters,secondary and derivative.The occurrence of disasters.For the low-risk areas such as the Hanshan County,the Luyang District and the Yaohai District of Hefei County,it is necessary to focus on improving the town's ability to prevent waterlogging,paying attention to the protection of the ecological environment while constructing flood control facilities,and strengthening the comprehensive monitoring of flood disasters to avoid secondary and derivative disasters.