The Value of Precipitation Forecasts to Anticipate Floods
L'importance des prévisions de précipitations pour anticiper les inondations
Busker, Tim ; Hurk, Bart van den ; Moel, Hans de ; Aerts, Jeroen C. J. H.
Recent disasters have highlighted the severe local impacts of extreme precipitation, including flash floods, landslides, and urban inundation. Despite significant investments in early warning systems, these events often catch many people off guard, emphasizing the need for a better translation of warnings into early actions. In this study, we directly address this gap by translating precipitation forecasts from the ECMWF, specifically the extreme forecast index (EFI) and shift of tails (SOT), to concrete triggers for early action. Our analysis reveals that such actions, triggered with a 2-3-day lead time, have a high potential economic value (PEV) across large parts of Europe. The SOT forecasts generally have higher economic value than EFI, especially at longer lead times. However, the effectiveness of both disappears across most of Europe with a 5-day lead. These results are based on comparing forecasts to the E-OBS dataset for extreme rainfall (>5-yr return period) over 8?years. We apply the optimal warning thresholds found in this analysis to the rainfall event that triggered the July 2021 western Europe flood disaster. Our results indicate that the EFI and SOT forecasts provided accurate and timely warnings at least 2-3?days in advance, aligning with flood impacts recorded in the Emergency Events Database (EM-DAT) dataset. Notably, on a 1-day lead time, the SOT forecasts accurately pointed to the Ahr catchment in Germany with highly exceptional values, providing strong indications of the disaster that unfolded there. This study underscores the value of these rainfall indicators and calls for further testing on more high-impact events.</p>
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