This layer (Figure 1) shows locations plotted as inverted triangles where flash flooding is forecast to occur over the next 5 days. Reporting points are plotted where the upstream drainage area is >=150 km2 and <=1000 km2.
The reporting points are produced using forecasts of precipitation and 2 metre temperature from the 7 km spatial resolution 20 member COSMO-LEPS ensemble numerical weather prediction model (NWP) and soil moisture forecasts from the EFAS hydrological system at 6 hourly temporal resolution. These inputs are re-sampled to 1 km spatial resolution and are used to calculate 6, 12 and 24 hourly accumulations of surface runoff on a 1 arc minute (~1.4 km) channel network.
The accumulations are compared against return period thresholds derived from an NWP reforecast climatology. This allows for the exceedance probabilities of the 2, 5 and 20 year return period thresholds to be calculated. Next the maximum exceedance probability for each return period across the 5 day forecast period is calculated. These maximum exceedance probabilities are compared against the classes shown in the third column of Table 1. At locations where one of the probability classes is satisfied, the corresponding inverted triangle is plotted at that location. The values next to each triangle correspond to the maximum exceedance probability of either the 2, 5 or 20 year return period threshold.
Figure 1: ERIC reporting points shown as inverted triangles. The blue lines show administration region boundaries. |
*RPxx = return period threshold level, e.g. RP5 is the 5 year return period. Table 1. The exceedance probability rules used to shade the reporting point triangles |
It should be noted that some of the reporting point triangles are plotted in a larger size. These triangles represent locations where the criteria for issuing an EFAS flash flood notification are satisfied.
- Probability of the flash flood return period (shown by the ERIC reporting points layer) exceeding the 5 year threshold is >= 30%
- Lead time to the event is <= 48 hours
- Catchment area >= 150 km2 and <= 1000 km2
The flash flood notifications are derived from the ERIC Reporting Points layer on EFAS which is under the Flash Flood layers heading. If an ERIC reporting point satisfies the criteria above, it is displayed as an enlarged triangle (Fig 1). However, only one enlarged triangle is shown within each administration region, if multiple points satisfy the flash flood notification criteria then the following checks are made:
- Identify the point with the earliest lead time
- If multiple points have the same lead time, select the point with the great exceedance probability of the 5 year flash flood return period threshold
Figure 1. Triangles show the ERIC reporting points, large triangles show locations where flash flood notifications would be issued. Dark blue lines show the administration region boundaries.
Reporting Point Pop-up Window
When one of the above reporting point triangles is clicked, the following information appears in a pop-up window.
1.Reporting point metadata
At the top of the pop-up window are two tables. The first is point information which shows the following:
- Country = name of the country where the reporting point is located
- CoA Status = Yes/No depending on whether the reporting point is located within an EFAS partner region
- Region = the name of the administration region
- River = the name of the river
- Upstream Area = the size of the catchment upstream of the reporting point
- Persistence = the number of consecutive previous forecasts in which a reporting point which satisfies the EFAS flash flood notification criteria has been present within the same administration region
The second table shows information about the landslide susceptibility:
- Very high = the total area upstream of the reporting point which has a landslide susceptibility classification of 'very high'
- High = the total area upstream of the reporting point which has a landslide susceptibility classification of 'high'
- Moderate = the total area upstream of the reporting point which has a landslide susceptibility classification of 'moderate'
Figure 2. Metadata about the flash flood reporting point shown in the pop-up window
2. Reporting point hydrograph
This shows the return period of the accumulated surface runoff return period for all ensemble members for all 6 hourly timesteps of the 5 day forecast period (Figure 3). The solid black line ('LEPS mean in the legend of Figure 3) represents the return period of the ensemble mean accumulated runoff. The dashed black lines show the accumulated surface runoff return period of the 30th (lower line) and 70th (upper line) percentiles from the ensemble. When the 30th percentile line exceeds the 5 year accumulated surface runoff return period (i.e. when the line enters the red box), this satisfies the flash flood notification criterion of a 30% exceedance probability of the 5 year accumulated surface runoff return period. The vertical dashed line represents the lead time of 48 hours, which is the maximum lead time at which flash flood notifications can be issued. The blue shading shows the ensemble spread of the accumulated surface runoff between the 10th to the 90th percentiles, darker blue shadings are shown closer to the 50th percentile.
The yellow, red and purple background shades represent the 2, 5 and 20 year accumulated surface runoff return period thresholds respectively. The values P(T>x)= show the maximum exceedance probabilities of the 2, 5 and 20 year accumulated surface runoff return period thresholds across the 5 day forecast period.
