3.4.3. Design Storms

Climatic variables' projections unto 2100 are forecasting within project RESCCUE. This study embraces these rainfall projections to create design storms (using alternating blocks method, according to recommendations produced near the study area [64]). After running the hydrodynamic model for the future expected conditions, including climate change influence, hence obtaining the pluvial floods to assess expected future impacts.

Extreme events analysis is considering return periods of one, five, 10, and 20 years as possible adaptation frameworks. The same rain intensity is distributed over the whole area for these synthetic events, with the rain gauges used for rainfall data acquisition process, and the cumulative rainfall (mm) for an event. These synthetic rains are conceived with a five-minute temporal resolution to reach a high-level accuracy, duration up to 2 h 30 min, and a maximum rainfall intensity as Figure 12 illustrates for each one of the return periods.

**Figure 12.** Synthetic rainfall events characteristics. Five-minute rainfall intensity hyetographs for events under current rainfall conditions: (**a**) A 1-in-1 year event; (**b**) a 1-in-5 year event; (**c**) a 1-in-10 year event; (**d**) a 1-in-20 year event. Five-minute rainfall intensity hyetographs for events under future rainfall conditions: (**e**) A 1-in-1 year event; (**f**) a 1-in-5 year event; (**g**) a 1-in-10 year event; (**h**) a 1-in-20 year event.

### **4. Results**

Section four highlights the research findings, focusing on the three key themes: The calibration and validation results obtained through hydrodynamic modelling of two historical flood events, from which there are real data to carry out the required corroboration; and the outcomes of the simulations under current and future rainfall conditions. This section outlines the modelling process results achieved via the application of the proposed methodology, their interpretation as well as the conclusions that can be drawn for three points: The calibration and validation phase. Besides, it shows the hydraulic modelling outputs from the application of the synthetic rainfall conditions driven by the impact of climate change into the drainage model.

With the results of the projected water depth for the conditions of the historical event used for the calibration of the model and the projected water depth for future flooding events, one of the two fundamental criteria is obtained. Along with the ridership flow to obtain the hazard and vulnerability assessment, the flood risk assessment results for Line 3 Metro stations are obtained, following the methodology introduced in Section 3.

### *4.1. Calibration and Validation Processes*

The first set of analyses examined the real events' pluvial flooding impact; one of them (2018-09-06) caused both surface flooding, along with two stations flooding on Metro Line 3, as indicated in Figure 13. The other flood event (2018-08-07) was merely superficial, comparable to the first event, but it did not generate flooding on Metro stations.

**Figure 13.** Calibration process summary output, for flooding event 2018-09-06: (**a**) Water depth modelling outcome in access 323\_1 that serves the Paral·lel Metro station; (**b**) photograph of the flood event in the Metro access surroundings, corroborating the water depth obtained in the modelling; (**c**) water depth modelling outcome in Paral·lel Metro station tunnel; (**d**) photograph of the flood event in the Paral·lel Metro tunnel, corroborating the water depth obtained in the modelling.

This real-life hydraulic behavior replication in the hydrodynamic modelling output is successful in obtaining similar water depths at the surface level, through the calibration process applying this model for the Barcelona master drainage plan and the executed process for this study. Moreover, for the first event, the model identified water entries to Line 3 surrounding Paral·lel and Drassanes Metro stations areas, including water in their tunnels, as can be seen from the table (below). Then, water depth results in the 2D hydraulic element surrounding the ventilation grates and Metro stations' accesses are summarized, in addition to the water level in the cited Metro stations, are consistent with the flood event records.
