*4.2. Main Results for Processing of Flooding Historical Records and Comparison with CS Simulation Results*

The results of the processing of historical records for the three return periods compared with the results of the model (1) simulations for current situation (CS as baseline) (Figure 3, for T=100 years) allow cross validating the results. Overall, the simulation results match with historical records for flood prone areas, especially for those near the river Tagus or areas where floods are more severe. As is evident from Figure 3, simulation results using a simplified network with only primary sewers do not provide full spatial coverage, with some areas with historical records likely to be associated with secondary sewers or rainwater inlets insufficiency. Additional model limitations such as simplified hydraulics, and the eventual occurrence of sedimentation and blockages not represented in the model, explain the apparent spare flow capacity in areas where flooding occurs regularly.

Historical records provide valuable information since the areas for each class of flood frequencies incorporate several records associated with each event and an extensive number of observations, and represent a proxy of the area for each flood frequency.





**Figure 3.** Use of sewer capacity at primary sewers (current situation (CS)-T100) and flood hazards based on historic observations.
