Adaptation pathways highlight urgent economic need to reduce flood risks in Europe

Given the commitment to sea level rise, massive and costly coastal adaptation is essential to reduce flood risks. Yet, the economically optimal timing of adaptation and adaptation tipping points remain unexplored on global and continental scale in coastal impact assessments. In this study, we model efficient adaptation pathways for 41,327 individual coastal floodplains along Europe's coastline through 2150. We consider three disaster risk reduction measures as potential adaptation options: protection, retreat and accommodation. Our assessment identifies the economically optimal timing for implementing these options, as well as the associated adaptation tipping points.

Using the state-of-the-art COASTPROS-EU dataset to model current coastal protection levels, we estimate that expected annual flood damages currently total USD 182 billion (2024 value). Immediate adaptation investments could drastically reduce these damages to USD 4 billion. For 95% of coastal floodplains requiring (additional) adaptation, the optimal timing for initial adaptation investments is now. We attribute this urgency to the vulnerability and exposure of coastal floodplains, which are already locked-in into existing conditions and are economically under-protected.

Adaptation tipping points, i.e. critical thresholds that require a shift from one adaptation option to another, are most prevalent along the Mediterranean coastline. In these regions, accommodation eventually becomes insufficient, requiring a switch to either protection or retreat to maintain efficient flood risk mitigation. These adaptation tipping points are driven by committed sea level rise due to past emissions, with their timing influenced by the rate of future climate change. On average, tipping points occur 29 years earlier under higher climate change scenarios (SSP5-8.5) compared to lower ones (SSP1-2.6).