Spatially explicit climate adaptation pathways for coastal archetypes: A quantitative narrative approach

Worldwide, coastal communities are increasingly at risk due to ongoing and accelerating sea-level rise, and adaptation is urgently needed to mitigate the effects such as the declining performance of coastal infrastructure. This study explores the development of fully quantitative and spatially explicit adaptation pathways for different coastal archetypes, focusing on the impact of sea-level rise on a gravity-based urban drainage system. Introducing conceptual decision narratives, we quantify synergies and trade-offs within such a framework, revealing spatiotemporal dependencies and how they evolve over time. Using the service decline trajectories for RCP4.5 and RCP8.5, we initially create a large ensemble of future pathways to explore adaptation timing, synergies, and trade-offs between service levels and economic losses. Our results show a strong dependence on the emission scenario, stressing the need for adaptive strategies and monitoring to track changes in risk. Nature-based storage and repurposing interventions were explored through different narratives, illustrating how these interventions can influence trade-offs between service levels, economic benefits, and timing. These trade-offs may not align spatially or temporally but can be managed through area-specific responses. By evaluating spatially explicit pathways in each archetype, we identified complex adaptation options with long lead times, such as managed retreat, and pinpointed timing conflicts and dependencies tied to development choices. To maintain flexibility necessitates identification of the right time to implement certain actions based on evolving scenarios and past decisions to avoid lock-in effects. Visualizing decision points, based on coping levels, thresholds, and economic considerations, can help decision-makers identify conflicting timelines or prevent maladaptive actions that lead to costly outcomes in the future.