Urban Flood Risk And Resilience Assessment Under Flood Scenarios

With the urbanization process,population and economic activities continue to gather in cities,increasing the vulnerability of urban systems to the impact of natural disasters,and under the dual influence of accelerating urbanization and global climate change,extreme rainfall occurs frequently,and the problem of urban flooding is becoming more and more serious,which has become an urgent problem for major cities to solve.This paper is based on disaster risk theory,resilient city theory,and the concept of resilient city.In this paper,based on disaster risk theory and resilient city theory,we use MIKE Urban coupled with MIKE 21 2D Overland model to build a 1D-2D coupled urban rainfall model and make full use of meteorological,geographic,hydrological,urban construction,social,economic and other data to build an urban flooding disaster risk and resilience assessment method based on flooding scenario simulation and a combination of subjective and objective flooding risk and resilience assessment.The research ideas and technical system of risk and resilience assessment are based on the flood scenario simulation and the subjective and objective method of flood risk and resilience assessment,and the research case of Yingtan City,Jiangxi Province is used to evaluate the risk and resilience of urban storm water flooding under the rain and flood scenario:(1)Construction,rate determination and validation of the research area rainfall flood model.Based on the meteorological,topographic and pipe network data,a 1D-2D coupled urban rainfall model was constructed for the old urban area of Yingtan City using the MIKE model,and the key parameters of the model were rated with the measured check well water level data.The model can better reflect the flooding situation in the study area.(2)Assessment of the current drainage capacity of the study area: Based on the simulation results,we analyzed the overloading of the pipe network under different recurrence periods,and thus assessed the current drainage capacity of the study area.The results show that the load of pipes increases with the increase of rainfall return period,and the drainage capacity of the drainage network in the study area is relatively general,with the percentage of pipes meeting less than 1-year return period,1 to 2-year return period,2 to 3-year return period,3 to 5-year return period,and more than 5-year return period being 21.11%,5.96%,3.25%,3.15%,and66.54%,respectively.The spatial distribution map of drainage network with different recurrence periods is drawn,and the spatial distribution characteristics of drainage capacity of pipe network are analyzed,and it is found that the drainage capacity of drainage network in the central city of Yingtan City shows obvious correlation with the degree of urban development and construction,because the study area is mainly the old city of Yingtan City,the urban development and construction is more intensive,the degree of land development is higher,the area and proportion of impermeable hardened sub-bedding surface is larger,and the regional However,the drainage network in the area was constructed early,the drainage design standard of the pipe network is low,the catchment area of the pipe canal far exceeds the design requirements and some pipes have structural defects such as deformation and rupture,so the drainage capacity of the pipe network is limited.(3)Construction of flood risk assessment framework based on rainfall scenario simulation.Based on the disaster risk theory,a total of eight evaluation indexes characterizing the risk,exposure and vulnerability of internal flooding were selected from the risk of internal flooding and the characteristics of the disaster-bearing body and socio-economic aspects,including water accumulation time,water depth,elevation,slope,population density,GDP density,drainage network density and drainage network density,etc.,based on the simulation results of the rainfall model under the 20-year and 50-year scenarios,GDP density,drainage network density,distance to medical institutions,and the combination of fuzzy hierarchical analysis and GIS analysis technology were used to calculate and analyze the spatial distribution of each influencing factor and comprehensive risk of internal flooding,and to draw a risk map of internal flooding in the study area.The results show that under the 20-year and 50-year rainfall scenarios,the overall spatial distribution of flooding risk in the study area is high in the central south and gradually decreases to the east and northwest,and the inundation area of medium and high risk areas is enlarged with the increase of rainfall intensity.The areas with higher risk and vulnerability to flooding are mainly concentrated in the traffic streets and riverside streets with high GDP density and population density in the central part of the study area,which are strongly correlated with the dense population and economic activities in the area by combining the spatial distribution characteristics of population density and GDP density,while the areas with lower risk to flooding are mainly concentrated in Siqing Street in the northwest of the study area.(4)Construct the evaluation model of urban rain and flood resilience in Yingtan under rain and flood scenarios.Based on the inherent logical fit between the resilience theory and TOPSIS model in terms of process and characteristics,this paper establishes an analytical framework based on TOPSIS model and the three main attributes of urban stormwater resilience,uses the fuzzy hierarchical evaluation method and entropy weighting method to determine the weights,and uses the Grey Relational Analysis(GRA)to identify and characterize the contribution and relevance of urban system’s stormwater resilience.The urban stormwater resilience evaluation model under the rainfall situation is constructed.The evaluation model is built from target layermedium layer-indicator layer,and a total of 17 indicators are selected from three layers of urban socio-economic resilience,ecological resilience,and infrastructure resilience to quantify the urban stormwater resilience level comprehensively,such as GDP per capita,land development intensity,and drainage network density,etc.The TOPSIS comprehensive evaluation results show that the overall urban stormwater resilience of Yingtan City from 2010 to 2021 The results of grey correlation analysis show that the contribution of urban infrastructure resilience evaluation indicators to urban resilience level is greater than that of socio-economic resilience and ecological resilience evaluation indicators.The urban infrastructure resilience evaluation indexes of land development intensity(C1),drainage pipe density in built-up areas(C6),and emergency drainage capacity(C7)have the largest contributions,the socioeconomic resilience indexes of GDP per capita(A1),population age structure index(A4),and population density(A6)have the largest contributions,and the ecological resilience has the largest contribution of green area per capita(B1).