**6. Conclusions**

This study presents a novel integrated model to simulate flooding in the underground Metro system of Barcelona. This model assumes that the Metro flooding only occurs from surface flooding that can drain into the underground Metro infrastructure through Metro staircases, ventilation grids, and elevators. The new model integrates a conventional 1D/2D urban flood model with a Metro model that is simulated as a system of pipes and links just as if it was a drainage network. The integrated model can simulate the spatial and temporal variability of Metro flood water depth and velocity. Simulated maximum flood depth is used as input for the flood risk assessment presented.

This research analyzes the current flooding of the Barcelona Metro Line 3 infrastructure, considering the climate change influence on future rainfall intensities, for flood risk assessment. This research proposed a framework for flood simulation of underground Metro systems, showing that Metro infrastructure can be simulated as a "drainage system" for risk assessment purposes of Metro systems. Notwithstanding the relatively limited data sample analyzing one of 12 Metro lines, this work offers valuable insights into developing targeted interventions aimed at reducing Metro service disruptions frequency and impact. This piece of research includes strategies to enhance flood risk management as a reasonable approach to tackle this issue, not only for Barcelona Metro but for Metro systems worldwide. This study provides a baseline for assessing potential flood outcomes in Metro systems, notwithstanding, any proposed adaptations are not studied in detail. However, the model can be used to evaluate adaptation measures' effectiveness. To estimate the adaptation costs under various climate change and socioeconomic development situations, compatible adaptation measures with the urban planning recommended by the Barcelona City Council are necessary.

One might thus conclude that decreasing Metro service flood hazard by heightening this infrastructure is further up the list of priorities, after ensuring pedestrian mobility at the ground level and easy access to Metro stations. Still, there are significant benefits from improving the flood hazard of flooding-exposed Metro infrastructure performing some adaptation measures, either increasing accesses' heights or achieving other structural measures such as hydraulic barriers by demand.

**Author Contributions:** Conceptualization, E.F.-O. and E.M.-G.; methodology, E.F.-O., E.M.-G. and B.R.; software, E.F.-O. and L.L.; validation, E.M.-G., L.L. and B.R.; formal analysis, E.F.-O. and E.M.-G.; investigation, E.F.-O., M.C.P. and L.L.; resources, E.M.-G., and M.C.P.; data curation, E.F.-O. and M.C.P.; writing—original draft preparation, E.F.-O.; writing—review and editing, E.F.-O., E.M.-G. and L.L.; visualization, E.F.-O. and L.L.; supervision, E.M.-G.; project administration, E.F.-O. and E.M.-G.; funding acquisition, E.M.-G. and B.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the RESCCUE project, which is sponsored by the European Union's Horizon 2020 research and innovation program under grant agreement No. 700174, whose support is gratefully recognized.

**Acknowledgments:** The contents of this research are a part of the findings of the project RESCCUE, which has obtained funding from the EU H2020 (grant agreement n. 700174). Part of the content is also presented in this article with the explicit consent of Transports Metropolitans de Barcelona (TMB). Re-use of the knowledge enclosed in this paper for commercial and/or non-commercial purposes is allowed and free of charge, on the requirements of compliance by the re-user of the research, not distortion of the original meaning or information of this research and the non-liability of the RESCCUE project partners and/or TMB for any consequence stemming from the re-use. The RESCCUE project partners and TMB do not accept any liability for the errors, consequences, or omissions herein contained.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
