Protection by hard defence structures or relocation of assets exposed to coastal risks: Contributions and drawbacks of cost-benefit analysis for long-term adaptation choices to climate change

Adapting to sea-level rise due to climate change involves new public policies that aim to relocate those assets most at risk from coastline erosion or flooding. It is no longer solely a question of studying the merits of a defence infrastructure project designed to prevent risks but of looking instead into a broader and longer-term project implying a whole new logic of land-use management for the areas concerned. In this context, the aim of the present article is to compare different adaptation scenarios and to show the need for evolving economic assessment and decision-making tools to include multidimensional and long-term aspects of adaptation policies. It is important to show the limitations of traditional Cost-Benefit Analysis (CBA) by integrating economic impact and non-market factors which are currently only assessed in multi-criteria approaches. Such assessments enable comparison of the Net Present Value (NPV) of a protection scenario using hard defence structures with various relocation scenarios, depending on whether the CBA includes only the direct damages avoided (classic CBA) or integrates the long-term tourist economy and environmental impacts (enhanced CBA). As costs of property purchasing are high, CBA may initially favour the protection scenario over relocations despite unfavourable tourist and environmental consequences. However, if one takes into consideration innovative land-purchase mechanisms which enable reduced investment costs in relocation scenarios, the latter measures may have a positive NPV. We therefore conclude that, in the long term, taking into account the local tourist economy and environmental benefits, the likely fall in prices of real estate at risk and the implementation of anticipatory schemes could enable relocation policies to become economically viable.