The method of predicting heavy tail of flood combined with regional envelope curve

The heavy-tailed behavior of floods indicates that the occurrence probability of extreme floods is greater than that predicted by the commonly used distributions with exponential asymptotic behavior, But in practical engineering applications, the heavy tail of floods in a basin may be caused by overestimating the frequency of extreme floods in that basin. The difficulty in predicting the degree of heavy tail leads to relatively large errors in the general empirical flood frequency curves. On the other hand, regional envelope curves are widely used to characterize the flood potential of various regions worldwide. We have developed a new method that combines regional flood envelope curves to predict and correct the appropriate flood magnitudes in similar regions, including dividing regions based on hydrological information and estimating the appropriate range of predicted floods through quantile regression. Flows exceeding this range are considered extreme and overestimated, while those below this range are considered to neglect the heavy tail and underestimated. In this study, we used flood data from at least 2,000 stations across China. Although the heavy tail of floods affects the flood frequency curve, the new method that combines regional flood envelope curves can better estimate the empirical frequency curve of the basin.