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This combination of flash flood hazard level with exposure gives impact levels for the river network cells. For each of the 4 lead time aggregation windows (0-6h, 7-24h, 25-48h, 49-120h), the cells show the maximum impact level forecasted throughout the window. To create this catchment level summary, the catchments are shaded according to the 90th percentile of the impact level of all cells forecasted within it. Use of the 90th percentile of impact (instead of the maximum) is to avoid communicating potentially misleadingly high forecast information to users based on single cell values.
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