The four layers show the flash flood impact levels forecasted for the upcoming five days, summarised at the catchment level. This forecasted impact level is estimated by intersecting a flash flood hazard forecast with static exposure data on a risk matrix. Both the flash flood hazard and the exposure data are split into three categories to create the risk matrix (Fig. 1).
Methodology Overview
The low, medium, and high values for flash flood hazard on the y-axis of the impact matrix indicate where there is a 5%-50%, 50%-80%, and >80% probability of exceeding the 2-year return period threshold. This flash flood hazard is estimated by comparing blended forecasts of precipitation (from the OPERA radar mosaic and ECMWF NWP forecasts) accumulated on the river network, with the reference values derived from climatology. This climatology is from:
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By clicking on specific catchments, users are able to see a pop-out window showing where in the impact matrix the catchment lies (Fig. 1). There is also some additional information on the number of people, education, health and energy generation facilities forecasted to be affected.
Selecting Forecast Date
If one of the TAMIR Catchment Summary layers has been chosen and no other TAMIR layers are already loaded in the EFAS webviewer, then by default the data will be loaded for the date which matches the date in the top right above the legend window (Fig. 2). Different dates can be selected using the date selection box in the top right above the legend window, but please note that it will only be possible to select data produced at 00 and 12 UTC on each day.
To select data produced at a specified hour within the past 5 days:
- Firstly either the TAMIR - impact forecast or the TAMIR - total precipitation 80th percentile layer must be chosen from the Flash Flood layers tab.
- An animation slider will appear in the bottom left of the webviewer (Fig. 2). Immediately above the animation slider is a drop down menu from which the specified date and time can be selected
- Once a date and time has been selected, this is automatically applied to all the TAMIR layers displayed in the legend window, including the catchment summary layers
Figure 2. Example of the TAMIR flash flood products loaded into the EFAS webviewer. The functionalities to load and manipulate the products are highlighted in red.
Suggested Use of the Catchment Summary Layers
These catchment summary layers can be very useful for identifying the general areas and time periods where flash flood impacts are possible. It is recommended that these layers should be consulted first before looking at the animated TAMIR - impact forecasts layer which can be difficult to visualise when zoomed further out and if you don't know the specific timesteps when flash flooding is possible. After using the catchment summary layers to identify the catchments and time windows where flash flood impacts are possible, the animation from the TAMIR - impact forecasts layer can be used to identify the specific 1 km grid cells and timesteps where impacts are possible.
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