Methodological Challenges and Strategies to Incorporate Climate Change into Flood Risk Analysis of Spanish Coastal Cities

Flooding of coastal cities may arise from a combination of coastal and inland flooding, which requires understanding complex correlations and dependencies between multiple drivers (precipitation, surge, tide...), and conducting joint analysis of future changes due to climate change. Mean sea level rise alone will already increase the probability of coastal inundation relative to fixed elevations from a combination of such drivers. Vulnerability of coastal cities is aggravated by the concentration of population and economic activity, with a continued upward trend in projection.

The above flood risk drivers pose an inevitable challenge to coastal cities, which must adapt to future flood risk conditions. Progress in this regard is being hampered, in the first place, by the lack of reliable methods for the evaluation of future risks. In this work we discuss the practical challenges encountered and the strategies and methods adopted to incorporate climate change into flood risk analysis of Spanish coastal cities (Bermúdez, 2017). We focus on the following aspects:

(1) The characterization of the joint behavior of the atmospheric and marine agents at the coast, and the evaluation of their hydrodynamic interactions. A continuous long term simulation method (Sopelana et al., 2018), in which historical time series of the flood drivers are simulated in a high resolution 2D flood inundation model, is applied to understand the interaction between the different sources of flooding and to provide detailed estimates of flood hazard.

(2) The derivation of local-scale projections of the required surface variables from the output of global climate models (GCM). Statistical downscaling techniques are applied to address the scale mismatch between the GCMs and the small-scale required for impact analysis, as well as to derive variables that are not available from GCMs.

(3) The evaluation of the uncertainties in the simulated climate change impacts. Flood risk maps are subject to uncertainties arising from the selection of climate models or the downscaling methods considered. A multi-model and multi-method ensemble approach is used to obtain an indication of the output plausibility.

References

Bermúdez, 2017. Research proposal "Flood risk analysis under global warming for long-term coastal cities planning". Athenea3i MSCA-COFUND Programme, University of Granada.

Sopelana, J., Cea, L., Ruano, S. 2018. A continuous simulation approach for the estimation of extreme flood (...). Natural Hazards 93(3), 1337-1358.