Study On Determination Model Of Rainfall Threshold For Different Durations Of Flash Flood In Small Watershed

Flash floods have brought huge losses to the people's lives and socio-economic conditions.The prediction and prevention of flash floods has become the focus of flood control and disaster reduction in our country.In recent years,under the condition of drastic global climate change,the short diachronic strong precipition is prone to occur frequently and the randomness and uncertainty of long-term rainfall process are more complicated leading to increasingly severe flash floods.So In this paper,according to the characteristics of different durations of rainfall,the short diachronic strong precipition are incorporated into the Rainfall threshold system of flash floods,Meanwhile,the Copula function is used to describe the randomness and uncertainty of the long durations of rainfall process,and establishes the determination mode of different durations of Rainfall threshold of flash floods.The main contents and research results of the paper are as follows:(1)Uncertainty analysis of influencing factors of Rainfall threshold in flash flood.In the process of determining the Rainfall threshold of flash flood,the two characteristic factors that the rainfall amount in the early stage and rain pattern are selected,and the independent factor disturbance method is used to analyze the influence degree of the two factors on the Rainfall threshold.Among them,the degree of influence of rainfall pattern and the rainfall amount in the early stage on Rainfall threshold is between 19%-47.2% and 5%-20%,which indicates that in the process of determining the Rainfall threshold,the degree of influence of rain pattern is greater than that of the rainfall amount in the early stage.(2)Short duration Rainfall threshold determination model of flash floods based on extreme precipitation.According to the characteristics of flash floods caused by short duration extreme precipitation,based on the analysis of the response relationship between short duration extreme precipitation and flash floods,and the Rainfall threshold amount for short duration was determined through the "extreme rainfall fitting module" and "disaster prevention capacity determination module",which can determine the short duration Rainfall threshold quickly and accurately,thus prolonging the early warning period of flash floods.(3)Long duration Rainfall threshold determination model of flash floods based on probabilistic rain patterns.Aiming at the long duration rainfall uncertainty,randomness and the characteristics of flash floods,the Copula function is used to construct the multi-parameter joint distribution function of total rainfall and rainfall at various periods,and further determine the probability rain pattern.At the same time,the trial algorithm was used to determine the Long duration Rainfall threshold based on the construction of a basin HEC-HMS model.(4)Rationality Analysis of Rainfall threshold in Flash Floods.According to the actual disaster-induced rainfall data in the study area,the time-interval characteristic rainfall assessment method and early warning model chart are used to analyze the reasonableness of the Rainfall threshold to improve the reliability of the model.