Coastal retreat as a serious option to adapt to sea-level rise

Published: 17 June 2021

Sea-level rise is expected to have severe consequences. To adapt to sea-level rise a range of options exists: protection, accommodation, coastal advance and retreat. So far, retreat has been mostly used post hoc, rather than preemptively. Researchers from Deltares, Utrecht University, New Zealand Climate Change Research Institute at Victoria University of Wellington, and Institute for Sustainable Development and International Relations demonstrate in the scientific journal Science how exploring pathways to managed retreat adds value in the context of the accelerating and long-term commitment to SLR. They argue that there is an urgent need to keep coastal retreat on the table as an option to adapt to sea-level rise.

Shrinking solution space

The effectiveness and feasibility of the adaptation options that are currently used is expected to decrease progressively with sustained and accelerating sea-level rise, compounded with other climate-related changes like intensification of extreme events and increased river flow along with increasing population pressures. That is not to say that retreat is easy for reasons of attachment to place, high sunk costs, lack of awareness and political resistance.

Alex Magnan (Institute for Sustainable Development and International Relations): “Retreat is inevitable in some places because sea-level rise and extreme sea levels are a growing and accelerating concern, and not all areas will have the capacity to respond. This is why staring now to progressively anticipate coastal retreat is key for the future.” Also, many decisions taken now have a long legacy into the future.

A dynamic pathways strategy

Exploring dynamic adaptive policy pathways can support the staging of retreat and help to break the retreat process into manageable steps over time. The long-term perspective of the approach puts a retreat strategy back on the table next to protection and accommodation measures. It can illuminate where and how retreat can have positive outcomes and avoid increasing investments that eventually become higher sunk costs. Lessons for pathways to coastal retreat include a) engaging early with affected communities to build understanding of their risk tolerance, vulnerabilities, and values; and b) avoiding developments in places recognized as risky and where existing urbanization trends can be reversed through no-build zones and prohibited land uses; c) considering whether buying time through temporary accommodation, protection, or nature-based measures will trigger greater risk exposure and therefore worsen the problem over time, or whether these approaches facilitate a transition to retreat.

Marjolijn Haasnoot (Deltares/Utrecht University): “Breaking adaptation into manageable steps and aligning it with other social goals such as infrastructure maintenance and environmental conservation, can help to highlight when to start retreat and to achieve positive outcomes of retreat. The adaptation pathways approach provides a structured way to adapt most effectively across this uncertainty.”

Practical pathways insights

Managed retreat is not a single action but follows a series of actions including community engagement, vulnerability assessment, land use planning, active retreat, compensation, and repurposing. Three generic stages can be identified: prepare, active retreat and clean-up. To determine when to start active retreat, one can assess under what conditions retreat is required because of limitations of other strategies, indicating the latest moment at which active retreat should commence. On the other hand, the retreat process could be realized when it becomes more beneficial than other strategies. If planned now and integrated with social, economic, and cultural goals, the anticipatory and dynamic pathways to retreat can be a positive approach to reduce coastal risks and minimize regret of investments and social inequities.

Judy Lawrence (New Zealand Climate Change Research Institute at Victoria University of Wellington): “ Retreat is a long term process and needs to start now through engagement with communities, increasing understanding that the risk levels are much higher than the past, designing funding and regulatory planning measures to avoid increasing the risk in currently exposed and vulnerable settlements and planning new developments in less risky areas while buying time through temporary adaptations such as protection and accommodation measures.“

Paper: M. Haasnoot, J. Lawrence, A. K. Magnan (2021) Pathways to coastal retreat. Science. 10.1126/science.abi6594