Joint Probability Analysis Of Event-based Rainfall And Its Application In Urban Flood Risk Assessment

Urban waterlogging will appear when the system can not afford the flow caused by heavy rainfall or continuous precipitation. Recently, with the rapid development of urbanization and the change of global climate, urban rainstorm flooding occurs more often than before, which has become the major natural disaster affecting the urban safety and development. Based on the previous researches of rainfall characteristics and flood risk, Taking into account the factor of peak intensity for flood risk, threshold analysis combined with the hydrodynamic simulations of drainage system is applied to probabilistic distribution of event-based rain storms, and an alternative probability method to urban flood risk assessment is proposed in this paper. The main research contents are as follows:(1) The method of urban flood risk assessment is applied and verified in Chengzhong catchment of a city in Zhejiang.30-year rainfall records of the city are reviewed. Individual rainfall events are identified with a suitable intervent time definition and then appropriate thresholds are used to select rainfall events that are most likely to cause flooding. The established hydraulic model are applied to simulate the performance of the drainage system under different rainfall situations. According to the analyses, a variate i is defined as the urban flooding index and sensitivity analyses are conducted between rainfall characteristics and i. The results show that peak intensity has an significant influence on urban waterlogging and average intensity and peak intensity are determined as the parameters characterized rainfall events.(2) Based on the determination of marginal distributions and dependence structure of rainfall variables, Frank Copula is utilized to describe the bivariate joint probability distribution of average intensity and peak intensity, which provides the theoretical basis for the analysis of the rainfall uncertainty. According to the scenario simulations of waterlogging, it is available to estimate the probability of flood risk in urban areas.(3) Considering the effect of the location of peak intensity on buffered drainage system, the trivariate joint probability distribution of average intensity, paek intensity and the ratio of precipitation before peak intensity is constructed. At the same time, a synethtic hyetograph in a double-rectangle shape is proposed to describe the inhomogeneity of temporal distributions of rainfalls. It is meaningful to the probabilistic description of event-based rain storms.