Cascading model uncertainty from medium range weather forecasts (10 days) through a rainfall-runoff model to flood inundation predictions within the European Flood Forecasting System (EFFS)

TLDR

Political pressure to provide medium‑to‑long‑term flood forecasts has risen after recent European flooding events. The study aims to understand cascaded uncertainties to deliver robust predictions. We feed 10‑day rainfall forecasts (deterministic, control, 50 ensemble) into LisFlood with six GLUE‑derived parameter sets, then propagate the 52×6 runoff realizations through LisFlood‑FP using ten GLUE‑derived roughness coefficient sets to generate uncertain flow hydrographs and inundation maps. The analysis shows that full uncertainty analysis is mainly limited by computational power and the representativeness of rainfall predictions, but the proposed approach is computationally feasible and can be improved in the future. Abstract.

Abstract

Abstract. The political pressure on the scientific community to provide medium to long term flood forecasts has increased in the light of recent flooding events in Europe. Such demands can be met by a system consisting of three different model components (weather forecast, rainfall-runoff forecast and flood inundation forecast) which are all liable to considerable uncertainty in the input, output and model parameters. Thus, an understanding of cascaded uncertainties is a necessary requirement to provide robust predictions. In this paper, 10-day ahead rainfall forecasts, consisting of one deterministic, one control and 50 ensemble forecasts, are fed into a rainfall-runoff model (LisFlood) for which parameter uncertainty is represented by six different parameter sets identified through a Generalised Likelihood Uncertainty Estimation (GLUE) analysis and functional hydrograph classification. The runoff of these 52 * 6 realisations form the input to a flood inundation model (LisFlood-FP) which acknowledges uncertainty by utilising ten different sets of roughness coefficients identified using the same GLUE methodology. Likelihood measures for each parameter set computed on historical data are used to give uncertain predictions of flow hydrographs as well as spatial inundation extent. This analysis demonstrates that a full uncertainty analysis of such an integrated system is limited mainly by computer power as well as by how well the rainfall predictions represent potential future conditions. However, these restrictions may be overcome or lessened in the future and this paper establishes a computationally feasible methodological approach to the uncertainty cascade problem.