E-Learning Module: Thresholds of Total Water Levels (TWL) for Triggering Coastal Flooding

The identification of local threshold of TWL for triggering coastal flooding aims to identify local thresholds that will trigger coastal flood mapping activity. It was necessary to identify both a total water level triggering threshold, used as a local reference to trigger the system in case of forecasted TWL exceedance, and a duration threshold, used to set the storm duration. In order to compute both thresholds, an Extreme Value Analysis (EVA) and a Duration Analysis (DA) were performed on the ECFAS combined hindcast. As the local TWL thresholds (triggering and duration) were identified using the ECFAS combined hindcast, and the system will instead be operative with the input of CMEMS forecast, a methodology was developed to establish a correction to be applied before integrating the thresholds into the warning system. The document also describes some limitations and possible future improvements of the employed methodology.

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Study a Little

Now that you understand a little about thresholds of total water levels and how they can trigger coastal flooding, you can read a little further via the following resources:

1. Harley, M., 2017. Coastal Storm Definition. In Coastal Storms (eds P. Ciavola and G. Coco), pp. 1-21, John Wiley & Sons, Chichester, UK.
2. Mentaschi, L., Vousdoukas, M., Voukouvalas, E., Sartini, L., Feyen, L., Besio, G., Alfieri, L. (2016). The transformed-stationary approach: a generic and simplified methodology for non-stationary extreme value analysis. Hydrology and Earth System Sciences, 20(9), 3527-3547, https://doi.org/10.5194/hess-20-3527-2016
3. Fernández-Montblanc, T., Vousdoukas, M.I., Ciavola, P., Voukouvalas, E., Mentaschi, L., Breyiannis, G., Feyen, L., Salamon, P., 2019. Towards robust pan-European storm surge forecasting. Ocean Model. 133,129-144, https://doi.org/10.1016/j.ocemod.2018.12.001
4. Vousdoukas, M. I., Mentaschi, L., Voukouvalas, E., Verlaan, M., Feyen, L., 2017. Extreme sea levels on the rise along Europe’s coasts. Earth’s Future, 5(3), 304-323, http://dx.doi.org/10.1002/2016EF000505

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For more information on coastal flood triggering in ECFAS see: https://www.ecfas.eu/public-deliverables/hindcasts-and-forecasts-of-coastal-flooding-triggers/