Impact of dependence in river flow data on flood frequency analysis based on regression in quantile plots: Analysis and solutions

Quantile‐quantile plots (QQ plots) are often applied to investigate tail behavior in extreme value analysis. When used for flood frequency analysis, based on river flow data, dependence in these data affects the extreme value distribution's tail behavior in the QQ plot. This problem is investigated on the basis of both synthetic and observed river flow series. The synthetic series are generated on the basis of a stochastic simulation procedure, which allows the real statistical flow properties to be known. Through simulation study, we demonstrate that serial dependence causes bending behavior in the QQ plot in the region of higher quantiles. This leads to the estimating error when the slope of the QQ plot is used as an estimator in the extreme value analysis. A correction method is proposed by modifying the plotting position using the extremal index. Key Points Establishing the effect of dependence in qq‐plots A solution on the impact of dependence on qq‐plots Simulation of river flow with known marginal distribution