Abstract
Flash floods cause great harm to people’s lives and property safety. Rainfall is one of the main causes of flash floods in small watersheds. The uncertainty of rainfall events results in inconsistency between the traditional single rainfall pattern and the actual rainfall process, which poses a great challenge for the early warning and forecasting of flash floods. To carry out the effective flash flood early warning and forecasting, this paper proposes a novel rainfall pattern by coupling total rainfall and peak rainfall intensity based on copula functions, i.e., the rainfall pattern of risk probability combination (RPRPC). On this basis, the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) hydrological model is used to simulate the rainfall-runoff process, the trial algorithm is used to calculate the critical rainfall (CR), and the optimistic-general-pessimistic (O–G-P) early warning mode considering the decision maker's risk preference is proposed. The small watershed of Xinxian in Henan province, China, is taken as a case study for calculation. The results show that the RPRPC is feasible and closer to the actual rainfall process than the traditional rainfall pattern, Frank copula function is the best for determining the joint distribution function of total rainfall and peak rainfall intensity, and the HEC-HMS model can be applied to small watersheds in hilly areas. Additionally, both RPRPC and antecedent soil moisture condition (ASMC) have influence on CR, and the variation of RPRPC will change the influence of ASMC on CR. Finally, the effectiveness of O–G-P early warning mode is verified.
Highlights
Flash floods refer to a sudden rise of the water level together with a significant peak discharge which are caused by heavy rainfall (Braud et al 2014)
Statistical induction based on data-driven methods, and the hydrology and hydraulics method (HHM), which is based on hydrology theory, are commonly used methods to calculate critical rainfall (CR) (Liu 2019)
A novel and practical rainfall pattern design method, which considers the uncertainty of rainfall pattern based on copula function, is presented through the risk probability combination of total rainfall and rainfall peak intensity
Summary
Flash floods refer to a sudden rise of the water level (within a few hours or less) together with a significant peak discharge which are caused by heavy rainfall (Braud et al 2014). Douinot et al (2016) assessed the applicability of the FFG method on French Mediterranean catchments using the MARINE hydrological model These hydrological models take into account the hydrometeorological and watershed characteristics of the study area, which can well simulate the hydrological process when flash floods occur. The uncertainty of rainfall pattern in small watersheds must be considered in the early warning and forecasting of flash floods. In view of the mentioned operational hydrology problems with the early warning and forecasting of flash floods, a novel design method for the rainfall pattern of risk probability combination (RPRPC) is proposed in this paper. (2) Based on the RPRPC, the HEC-HMS model is used to simulate the rainfall-runoff process in a small watershed, and the trial algorithm is used to calculate the CR threshold space in a multiscenario mode.
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