Probabilistic coastal flood risk assessment under climate change using holistic socio-economic-environmental indicators

Abstract:

Climate change and rising sea levels are increasing flood hazards for coastal communities. Flood risk assessments are essential as the basis of decisions to support flood risk reduction. However, most flood risk assessments target only economic damages, providing a single-sided picture of risk. Further, many flood risk assessments address a single catastrophic flood hazard scenario, instead of assessing risk across many likelihoods. In this research, we conducted a probabilistic flood risk assessment (i.e., with consideration of multiple likelihoods) for the District of Tofino, a coastal community on the West Coast of Vancouver Island, Canada. We assessed risk for the present and 3 future sea level rise (SLR) scenarios, for a wide range of holistic indicators, including social, economic, critical infrastructure, environmental and cultural aspects. The development of indicators and associated data proxies was supported by community stakeholder workshops, where we obtained information on local values, as well as local knowledge on exposure and consequences, and more traditional spatial exposure datasets. For each indicator, we developed exceedance probability curves. These visualized consequence thresholds with changing likelihoods and rising sea levels, and highlighted that typically, the effect of SLR was more pronounced than that of coastal storm intensities. We also calculated the average annual loss for each indicator, and developed gridded risk maps for the study area, which visualized risk (as the average annual loss) for each grid cell. Based on this holistic analysis, we were able to identify high flood risk areas, and provide detailed recommendations to local stakeholders, which did not only include monetary (tangible) aspects, but also more intangible aspects such as environmental contamination, or cultural impacts (e.g., to Indigenous cultural sites). Further, the probabilistic approach also allowed the capturing of both the consequences of catastrophic floods, and of small but frequent floods, where consequences add up cumulatively over the years. The novel approach presented in this research is applicable to other risk assessments, and can support the development of well-rounded flood risk reduction measures, as communities adapt to increasing flood risk under climate change.