The European Copernicus Coastal Flood Awareness System (ECFAS) project will contribute to the evolution of the Copernicus Emergency Management Service (https://emergency.copernicus.eu/) by demonstrating the technical and operational feasibility of a European Coastal Flood Awareness System. Specifically, ECFAS will provide a much-needed solution to bolster coastal resilience to climate risk and reduce population and infrastructure exposure by monitoring and supporting disaster preparedness, two factors that are fundamental to damage prevention and recovery if a storm hits. The ECFAS Proof-of-Concept development will run from January 2021-December 2022. The ECFAS project is a collaboration between Scuola Universitaria Superiore IUSS di Pavia (Italy, ECFAS Coordinator), Mercator Ocean International (France), Planetek Hellas (Greece), Collecte Localisation Satellites (France), Consorzio Futuro in Ricerca (Italy), Universitat Politecnica de Valencia (Spain), University of the Aegean (Greece), and EurOcean (Portugal), and is funded by the European Commission H2020 Framework Programme within the call LC-SPACE-18-EO-2020 - Copernicus evolution: research activities in support of the evolution of the Copernicus services. This project has received funding from the European Union’s Horizon 2020 programme The deliverables will have restricted access at least until the end of ECFAS Description of the containing files. The present work aimed to identify the required level of complexity in numerical models for a more accurate representation of coastal water-levels used as marine forcing in coastal flood warning applications such as ECFAS. The level of complexity is evaluated in terms of added physical processes as well as by analyzing different configurations of the models. To this aim, the model systems used in ECFAS to produce hindcasts -ANYEU-SSL (2D) for the European region - and forecasts -CMEMS (3D) for the northeastern Atlantic region (Iberia Biscay Ireland, IBI)- were tested (ECFAS D4.1 - Report on the calibration and validation of hindcasts and forecasts of TWL). Two physical processes were considered: the surge and tide non-linear interaction and the wave and surge non-linear interaction. The models show moderate to strong sensitivity to both processes, in particular during extreme events, highlighting the potential importance of these processes for accurate numerical predictions of extreme coastal total water-levels. The derived limitations and future recommendations are presented, in the context of the possible future roadmap of integration of the ECFAS system into the Copernicus Emergency Management Service. Disclaimer: ECFAS partners provide the data "as is" and "as available" without warranty of any kind. The ECFAS partners shall not be held liable resulting from the use of the information and data provided. This project has received funding from the Horizon 2020 research and innovation programme under grant agreement No. 101004211