*4.4. Final Ranking: Results of the Detailed Assessment*

The results from the detailed assessment provided information to generate four prioritization rankings relevant for stakeholders (Tables 9 and 10), three of them contained monetary criteria—avoided damage, net benefits and costs, and one was in percentage terms, representing the high-risk area reduction.


**Table 9.** Prioritization results under the 3 monetary criteria for pluvial flooding in Barcelona.


**Table 9.** *Cont.*

**Table 10.** Prioritization results under high-risk area reduction criterion for pluvial flooding in Barcelona.


The aim was to provide as much information as possible to solve the concerns of decision makers regarding the different aspects of the policy making process, i.e., budgetary, welfare, and risks. The BAU scenario is omitted from the ranking as the objective of the city council is to act against floods. For the avoided damage and risk reduction criteria, the preferred scenario is to implement SUDS and structural measures in the entire city of Barcelona; whereas for the net benefit criteria, the scenario with SUDS and structural measures in zone 5 ranks first. In the case of cost criteria, the SUDS measures are the preferred option. The zone 5 scenario also ranks high for the rest of the criteria. This is expected to support stakeholders by facilitating the decision-making process of implementing adaptation measures. More detailed results of the risk assessment can be found in Appendix B.

The prioritization exercise for the CSO strategy (Table 11) was carried out using 3 monetary criteria (i.e., avoided damage, costs, and net benefits), using the outputs from the CBA that used the damages analysis results.

**Table 11.** Results of ranking of adaptation scenarios selected for CSO under the three selected criteria in Barcelona.


These results helped decision-makers to understand the most advantageous adaptation measures given their selected criteria, which might be subject to maximizing net welfare gains, or minimize costs or damages. If the avoided damage and net benefits criteria are considered, the scenario of combined SUDS and tanks was preferred, whereas if the criterion follows cost-efficiency, the SUDS scenario ranked first.

The results of the detailed assessment carried out in the Bristol case study provided a rank based on the total damage costs expected during a range of extreme flood events in the city for pluvial and tidal/fluvial flood scenarios (Tables 12 and 13).



**Table 13.** Estimated total flood damages resulting from extreme tidal/fluvial flood events to all building classes for different return periods (T*year*s) (£) in Bristol.


The analysis identified that the most effective intervention scenario was individually targeted property level protection to reduce the impact of both pluvial and fluvial flooding hazards. The results of the total damage assessment, of the previous CEA and co-benefits results were detailed enough for stakeholders, and therefore a complete CBA was considered not necessary for Bristol's decision-makers. Instead, stakeholders were more interested in understanding the changes pertaining to the traffic and energy sectors when the selected scenario was applied. Therefore, in the traffic sector, the effectiveness of the adaptation scenario was evaluated by comparing the reduction in recovery time, vehicular cost estimations with respect to their average speed, and PMx emissions, under flooded conditions compared to dry weather conditions [61]. The energy sector's detailed assessment compared the BAU scenario to the selected scenario under different levels of fragility curves of the electrical substations, to provide further information to decision makers on the potential impacts reduction generated by the measures proposed [49].

### **5. Discussion**

The present methodology is built upon existing knowledge of applied quantitative and qualitative methodologies related to urban climate change adaptation and resilience. The flexibility of the methodology was a key feature, and it has been achieved by introducing iterative stakeholder engagement in each stage. The fact that multidisciplinary research groups worked along with city councils and other stakeholders, gave the methodology a practical focus that included tools to face the most common barriers and opportunities met by most climate change adaptation working groups, such as lack of data sources. The methodology offers a modular system that is able to adapt to the realities of the different case studies, allowing to select the required steps for each case. Another

advantage is the use of existing and proved methodologies, which are common to stakeholders, with known strengths and weaknesses.

The potential to combine technical, economic, social, and environmental results is a powerful policy instrument, as their decision-making process must consider all those aspects that affect the present and future of their citizens' welfare [2]. It is particularly relevant for those cases where there are many measures that need to be screened and not enough time or capital resources to do so with the necessary detail to support policy decision-making. In that sense, co-benefits assessment in climate adaptation projects can contribute substantially to policy decision-making [62]. First, it is suggested that most co-benefits display positive welfare outcomes in the short term—for example, air pollution improvement, which is the concern of policy makers; whereas direct climate change policy benefits—such as heavy flood damage reduction—may only be perceived in the long term. Second, the co-benefits are usually enjoyed at a local or regional scale and thus are closer to the citizens bearing the costs, they provide incentives for decision makers to act [62].

The methodology enabled the views and expertise of multiple stakeholders to be included through workshops. It has the benefit of fewer requirements from the CEA during the first stage, although the outcomes lack sound conclusions. The uncertainty of results decreases with the participatory process of multidisciplinary experts and further detailed assessment to the selected measures.

The involvement of policy-makers from the beginning of the analysis was regarded as positive, compared to traditional approach of just presenting final results through an assessment report. In addition, such an engagement captured local expertise, enabling intervention development to progress with the understanding of specific high-risk areas and ongoing organizational initiatives. The stakeholder engagement was also able to capture mixed priorities from different groups and integrate this understanding within the context of a wider RESCCUE analysis, drawing together a network of interconnected infrastructure, including the energy, transport, and waste-water sectors. If consultation is transparent and well-structured, it can give valuable insights of local knowledge [27].

Although the focus of the present work is on urban infrastructure and services, it does not neglect social-oriented policies. However, it recognizes that these "soft" policies, such as encouraging residents to change public behaviors [63], belong to a different field of study and policy-making process, out of the scope of this work. However, the final goal of both types of policies is similar: to increase wellbeing, either from a psychosocial perspective or by reducing physical risks and damages.

One of the main barriers for urban adaptation assessment is the general lack of standardized data and/or time resources. Adapting the approach to accommodate varying data availability was an additional challenge. Furthermore, researchers found difficult to align work across stakeholders and case studies, due to existing differences in policy approaches, priorities, and types of stakeholders and their involvement. Another drawback of the methodology is that the co-benefits are city-specific and subject to the expert criteria. Analyses based on experiences, data, and perspectives from stakeholders are based on historical hazard impacts, rather than providing a true representation of future risks. This potential bias can be minimized if robust climate change forecasting and risk and damage modeling is introduced in the assessment. Therefore, although the hydrological model (suggested in the methodology to assess the recovery time) increases the technical expertise demand in the preliminary stage, it is essential to secure informed decision-making throughout the process. In addition, it is an established technique, and the exercise is not as complex as the detailed damage and risk assessment proposed in the third stage, which is highly recommended for final decision-making.

A limitation of an approach grounded in stakeholder engagement is the need to manage conflicting priorities and adjust messages to an audience with varying levels of expertise. This is particularly relevant when managing organizational and community stakeholders, where costs and benefits of intervention actions may not be aligned. Unconscious bias, such as exposure to specific hazards or experience may also influence engagement, leading to a focus on specific issues at the expense of a broader analysis. These issues have been addressed in RESCCUE through engaging a diverse group of technical stakeholders who shared their expertise and results to multidisciplinary audiences.

Similarly, highly spatial hazards such as pluvial flooding can be very dependent on unknown or unpredictable factors which may not have occurred during past events; for example, aging infrastructure may block previously functioning drainage features and significantly alter the response of urban catchments rainfall. These issues cannot be fully mitigated, and for that reason, it was crucial that the methodology recognized those limits by including historic and experiential data. In fact, the consequences of a changing climate and the continuing paving of urban areas (increased permeability) lessen the validity of decision based on historical facts.

Future recommendations to expand the replicability potential is to create a web-based assessment tool to facilitate the implementation in other urban areas.
