Study On Dynamic Early Warning Model Of Flash Floods Based On Rainfall Numerical Forecast

The forecast of flash floods are constantly developing in the direction of refinement,and higher requirements are put forward for the accuracy of the forecast.Disasters often have the characteristics of short duration,which limits the application of rainfall numerical forecast products in the forecast of flash floods.In order to apply rainfall numerical forecast products to the early warning and forecast of flash floods,this paper proposes a method of correcting rainfall forecast based on meteorological elements and a method of decreasing time scale based on probabilistic rain patterns.The numerical correction and decreasing time scale of rainfall numerical forecast products.In addition,this paper uses the HEC-HMS model to establish a flood forecast ensemble,and considers the damage depth(D)and the probability of the flood process(P),and uses the theory of information entropy to establish a flash floods early warning model.They were tested in the Tengzhou watershed,Xinxian watershed and Luofubao watershed.The main research contents and results are as follows:(1)Research on the adaptability of rainfall numerical forecast products in typical small watersheds through TS scores and forecast deviations.The maximum value of the European Center for Medium-Term Weather Forecast(ECMWF)ensemble forecast has the ability to forecast rainstorms and above.Stronger,so it is more suitable for early warning and forecasting of flash floods in small watersheds.At the same time,a correction method of rainfall numerical forecast based on meteorological elements is proposed.The average relative error of the correction value of this method in a typical small watershed is less than 20%.(2)The Copula function is used to combine total rainfall and peak rainfall to establish a probabilistic rain pattern,and to reduce the time scale of the rainfall correction value of the rainfall numerical forecast product.The results obtained by the down-time scale method conform to certain statistical laws,so the down-time scale method is reasonable to a certain extent,and can provide technical support for the application of rainfall numerical forecast products to flash floods in small watersheds.(3)Based on the theory of information entropy,FFAI early warning indicators were proposed,and the early warning model of flash floods was established.The flood forecast ensemble was established through the HEC-HMS model,and the warning model was tested by selecting typical disaster prevention sections and flood events in three different watersheds.The results show that the early warning model of flash floods has good applicability in small mountainous watersheds,and provides new ideas for early warning and forecast of flash floods.