Infrastructure in low-lying coastal areas faces challenges from climate change, sea level rise, and the impact of compound hazards. Dynamic adaptive pathways planning (DAPP) is increasingly being applied as a way of planning under deep uncertainty. Stress testing for robustness is an integral part of DAPP which provides decision-makers with confidence. We outline a seven-step approach—combining scoping workshops, systems mapping, DAPP, exploratory modelling, robust decision-making, real options analysis and validation workshops—to support decision-making for infrastructure in low-lying coastal areas. We apply the seven steps to two wastewater treatment plant (WWTP) case studies in New Zealand to quantify indicators, signals, triggers and adaptation thresholds within DAPP plans and to identify adaptation pathways that are robust against future uncertainty. Case study one focuses on the implementation of an existing DAPP at Helensville WWTP. Our modelling enabled the challenge of quantifying indicators for adaptation thresholds and triggers to be overcome. We show that an adaptation threshold occurs at 31 cm of RSLR, the trigger point is sufficient lead time to enable relocation, and the indicator is the rate of observed RSLR. Case study one demonstrates in a quantitative way how an existing DAPP can be functionally implemented by a water management agency. Modelling for case study two, the Seaview WWTP, showed that 26 cm and 56 cm of RSLR are key thresholds. Nuisance flooding may occur after 26 cm of RSLR, which could happen as early as 2040 under a high emissions scenario. Inundation of plant assets may occur after 56 cm of RSLR, which could occur as early as 2060. Modelling showed that implementing changes to plant layout would allow the plant to remain on site for its design life (until 2080). Five adaptation archetypes were developed—sequences of adaptive actions that achieve the performance objective of continuing levels of service and avoid inundation of WWTPs. The seven-step approach is a way to stress-test a DAPP, to quantify signals, triggers and adaptation thresholds and to simulate implementation of a DAPP under a range of scenarios. This can facilitate more robust decision-making for wastewater infrastructure assets under future uncertainty.

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Adaptive pathways planning is an approach that maps the solution space over time to inform decision making under uncertainty. Since its first applications to climate change adaptation in the ’10s several studies and practical applications have used and extended the approach and discussed its benefits, limits, and complexity. What have we learned from a decade of adaptive pathways studies? This paper elaborates lessons learned on the use, value and weaknesses of adaptive pathways approaches for decision making using a set of guiding questions related to the decision context, the methods used, and contributions to decision making. Based on our experience and literature review, we find that: a) adaptive pathways analyses have been applied widely and are moving from theory to practice; b) an adaptive pathways analysis can be tailored and typically follows a staged approach; c) methods include narratives, impact models, and stakeholder participation tools; d) the complexity of adaptive pathways as a result of multiple actors, values, hazards, and actions at various scales for different purposes is a challenge, and this is increasingly considered through various extensions and combinations with other approaches. Ways forward to address weaknesses and current challenges include: accounting for coevolution between multiple actors across different scales (e.g., through interactive and multilevel pathways) and combining an adaptive pathways analysis with visioning and backcasting approaches for transformative adaptation and operationalizing climate resilient development pathways. To enable further applications in practice, it is important that experiences are shared and governance issues (e.g. long-term planning and funding) addressed.@en