Determination of the distribution of flood forecasting error

Flood forecasting plays an essential role in enhancing the safety of residents downstream and preventing or reducing economic losses. One critical issue in flood risk assessment is the determination of the probability distribution of forecast errors. Several investigations, which have been carried out to analyze the influence of the uncertainty in real-time operation or water resources management, assumed that the relative forecast error was approximately normally distributed. This study investigates whether the flood forecast error follows the normal distribution. Several distributions were fitted to the flood error series, and their performances were analyzed using the data from Three Gorges Reservoir (TGR) and Muma River. Then, the most appropriate distribution was selected. Results show that the assumption of normal distribution is not justified for the flood forecast error series of TGR and Muma River. The use of normal distribution for estimating flood risk may lead to incorrect results.