The influence of antecedent catchment conditions on seasonal flood risk

Abstract
A model is proposed which estimates the probability of the flow in a river exceeding a given discharge during a period of 1 month conditional on the catchment wetness at the start of the month. The model is fitted to data selected on the basis of a rainfall threshold. It assumes a Weibull distribution of flows conditional on rainfall and catchment wetness. The model is applied to the River Browney and the River Aire in the north of England. Base flow in the river is used as a measure of catchment wetness. Extreme value distributions are fitted to the rainfall and base flow data independently, and a Poisson distribution is assumed for the number of exceedances above the rainfall threshold in each month. The results from these catchments show that the antecedent catchment conditions significantly affect the flood risk.

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