Generic adaptation pathways for coastal archetypes under uncertain sea-level rise

Abstract

Adaptation to coastal flood risk is hampered by high uncertainty in the rate and magnitude of sea-level rise. Subsequently, adaptation decisions carry strong risks of under-or over-investment, and could lead to costly retrofitting or unnecessary high margins. To better allocate resources timely and effectively, and achieve long-term sustainability, planners could utilise adaptation pathways, revealing the path-dependencies of adaptation options. This helps to identify low-regret short-term decisions that preserve options in an uncertain future, while monitoring to detect signals to adapt. A major barrier to the application of adaptation pathways is limited experience. To facilitate this, here we generalize this pathways approach for six common coastal archetypes, resulting in generic pathways suitable to be adjusted to local conditions. This provides a much richer analysis of coastal adaptation than provided by any previous analysis, by assessing the solution space and options over time for a variety of coastal regions. Based on this analysis, we find that the number of adaptation options declines while sea-level rises. For some archetypes, it becomes clear that long-term thinking is needed now, about if, how and when to move to transformative options, such as planned retreat, which may presently not be considered or acceptable. Our analysis further shows that coastal adaptation needs to start earlier than anticipated, especially given time required for local debate and choice and to implement measures.

Usable Science for Managing the Risks of Sea‐Level Rise

“…These efforts have concentrated on understanding the nature of uncertain hazards, exposure, and vulnerability—which together constitute risk in the sense used by the Intergovernmental Panel on Climate Change (Lavell et al, )—as well as the translation of research into practice (Bhave et al, ; Dessai et al, ; Hallegatte, ). Decision frameworks fall into two major categories: traditional “prediction‐first” economic perspectives, such as benefit‐cost analysis, cost‐effective analysis, and multi‐criteria analysis; and more policy‐driven approaches, such as robust decision making and Dynamic Adaptive Policy Pathways (Dittrich et al, ; Gorddard et al, ; Haasnoot et al, , ; Lempert et al, ; Lempert, ; Wise et al, ).…”

“…Unlike traditional approaches, where the emphasis is on converging towards an optimal solution, robustness is defined by the identification of mechanisms that can show satisfactory performances under different initial conditions, assumptions about prior probability distributions, and models of the system (Lempert et al, ; Lempert & Collins, ). Implemented through computational simulations assisted by scenario‐based planning and adaptive management, the RDM process allows decision makers to work with stakeholders in the identification of vulnerabilities, opportunities, and trade‐offs among possible adaptation responses (Haasnoot et al, , ; Lempert, ).…”

“…This paper provides an overview of the sea‐level science relevant to decision makers and communities developing forward‐looking coastal adaptation strategies. Ultimately, such strategies must identify ways to combine the four basic approaches to coastal adaptation (e.g., Haasnoot et al, ; Sengupta et al, ): (1) accommodation of more frequent flooding through social (e.g., improved emergency response), economic (e.g., flood insurance), and engineering changes ; (2) defense against flooding; (3) advance (i.e., the reclamation of land from the ocean); and (4) relocation (e.g., through autonomous or planned migration). Determining how to combine these approaches requires consideration of the physical hazards associated with sea‐level change and the autonomous responses of individuals to their changing environment, as well as the decision science approaches that can help construct strategies that are robust to uncertainty and the political and sociological barriers to their effective use.…”

Framework for High‐End Estimates of Sea Level Rise for Stakeholder Applications

“…Among these users, those requiring high-end scenarios are primarily those recognizing that their management decisions may lead to maladaptation traps (Magnan et al, 2016) above a certain amount of sea level rise or sea level rise rates. Here, high-end scenarios can be useful to estimate if and when the resilience capacity of each community could be exceeded and what choices this raises in terms of adaptation (advance, protect, accommodate, and retreat; Nicholls, 2018;Haasnoot, Brown, et al, 2019). This includes the iterative approach to risk management promoted by the IPCC (Jones et al, 2014) that acknowledges the climate is changing and we need to consider not just changing hazard but also changing exposure and vulnerability through a risk management lens (Figure 1).…”

“…Without adaptation, sea level rise increases flood frequency and reduces time for recovery, challenging to local capacities to maintain acceptable safety standards and appropriate expectations of economic damages. Here, high-end scenarios can be useful to estimate if and when the resilience capacity of each community could be exceeded and what choices this raises in terms of adaptation (advance, protect, accommodate, and retreat; Nicholls, 2018;Haasnoot, Brown, et al, 2019).…”