*3.1. Methodology Main Steps*

The overall methodology proposed to undertake the spatial characterization of the flood related hazards has the following main steps:


The methodology adopted for hazards identification takes the data obtainable for the investigation and available tools into consideration to diagnose and evaluate the effect of climate change scenarios in terms of flood related hazards as a route to ascertain resilience of urban services to these events. Both data and models have inherent limitations and uncertainties and research design is grounded on the use of complementary methods, in a triangulation-based approach [25], using multiple methods to study the research problem [26]. Methodological triangulation allows adding reliability and validity to the results and cross checking of results [27], taking advantage of overlapping and intersecting layers of geographic information. For the study case of Lisbon, the set of methods, available for the triangulation to support flood risk identification, are identified. The structure adopted in this study is given in Figure 1.

**Figure 1.** Methods triangulation for characterization and mapping of flooding related hazards.

Assumptions in this study include the focus on the water cycle and flood related hazards, while the risk sources analysed are rainfall and coastal overtopping [10]. The emphasis here is on the mobility and waste management sectors, but the methodology is applicable to other urban sectors.

#### *3.2. Tools and Data to Support Risk Identification*

The first step is to identify the data and tools available for the study case to support the methodology refinement; the methodology takes into account current and future situations while considering climate change.

In terms of tools, two types of hydraulic mathematical models are available for the city of Lisbon [28,29]: (1) the City wide 1D GIS model; (2) the Downtown catchments JL using 1D/2D combined model (SWMM and Basement) [30,31]. These models have a number of limitations in the data for model building and confirmation, but the two models do represent a balance between spatial scope, level of detail and data availability. The former (1) covers the city as a whole but adopts a simplified hydraulic model and sewer network; the later (2) uses a more robust hydraulic formulation and includes network as well as overland flow simulation.

For the study case of Lisbon, the set of methods available to support description and mapping of flood related hazards are indicated in Figure 2, together with main outputs and hazard characteristics.

The approach adopted in method 1, a qualitative method, allows for collaborative crosscheck, where groups or individuals with different points of view investigate common issues involving interrelated systems and services, increasing the validation and consolidation of the aspects

evaluated [32]. With this approach, identification of flood related hazards and risk factors for strategic urban services was developed in a collaborative process involving representatives of the Lisbon city services included in the study. Stakeholders with direct involvement are listed in Table 2. Following the consultation sessions with stakeholders, the analysis of results for the study case resulted in an interdependencies matrix. The structure and aims of the study and focus on issues related to flooding in this specific city has determined the level of involvement of the stakeholders.

**Figure 2.** Methods for characterization and mapping of flood related hazards and outputs.


**Table 2.** Main stakeholders involved in the Lisbon city study case.

\* Includes a range of urban services, e.g., civil protection, wastes, public lighting, urban planning, mobility and environment.

For method 2, data from a historical events register, currently updated by the civil protection services, was used to assess citywide flood frequency.

In method 3, the citywide model approach (1) the hydraulic modelling simplified study of the drainage system (1D GIS model), was based on a conceptual model due to the complexity of Lisbon's drainage system and data limitations. This simulation tool uses GIS routines and was implemented on ArcMap ™ software. This model was built with the primary sewer network, to enable modelling of major physical and hydrodynamic properties of the system. This model includes 421 sub-catchments, 797 junctions and 753 sewers, which make up a total of 173 km, around 12% of the whole sewer network length. From the 797 junctions, 218 are head junctions and 48 are final junctions, which discharge to a main trunk system (primary sewer conveying wastewater to the treatment plant), the Tagus River (receiving water body) or to neighbouring councils' sewers. Secondary sewers (cross-sections smaller than 800 mm) are not included.

In method 4, for the Lisbon Downtown catchments J-L, the 1D/2D SWMM and BASEMENT combined model was set to allow for estimating the flooded areas and its water levels at the surface. These catchments were selected because they are two of the most flood prone catchments in Lisbon, encompassing historical and touristic downtown areas with relevant infrastructure and services. The

model for this area includes 32 sub-catchments, 331 sewers and 318 nodes, from which six corresponded to outfalls [28,29].
