A Flood Damage Allowance Framework for Coastal Protection With Deep Uncertainty in Sea Level Rise

Abstract

Deep uncertainty describes situations when there is either ignorance or disagreement over (1) models used to describe key system processes and (2) probability distributions used to characterize the uncertainty of key variables and parameters. Future projections of Antarctic ice sheet (AIS) mass loss remain characterized by deep uncertainty. This complicates decisions on long‐lived coastal protection projects when determining what margin of safety to implement. If the chosen margin of safety does not properly account for uncertainties in sea level rise, the effectiveness of flood protection could decrease over time, potentially putting lives and properties at a greater risk. To address this issue, we develop a flood damage allowance framework for calculating the height of a flood protection strategy needed to ensure that a given level of financial risk is maintained. The damage allowance framework considers decision maker preferences such as planning horizons, protection strategies, and subjective views of AIS stability. We use Manhattan—with the population and built environment fixed in time—to illustrate how our framework could be used to calculate a range of damage allowances based on multiple plausible scenarios of AIS melt. Under high greenhouse gas emissions, we find that results are sensitive to the selection of the upper limit of AIS contributions to sea level rise. Design metrics that specify financial risk targets, such as expected flood damage, allow for the calculation of avoided flood damages (i.e., benefits) that can be combined with estimates of construction cost and then integrated into existing financial decision‐making approaches (e.g., benefit‐cost analysis).

The Political Complexity of Coastal Flood Risk Reduction: Lessons for Climate Adaptation Public Works in the U.S.

“…For these reasons, knowing why projects fail is also useful not only for proponents but also for those who wish for a particular project to fail. Rather than thinking of protection strategies that focus on a single, critical threshold (e.g., the 100‐year flood; Rasmussen et al., 2020), a more diverse suite could be used, such as those that are redundant, “safe‐to‐fail” (Kim et al., 2017), more affordable, combine natural and built infrastructure (Sutton‐Grier et al., 2015), and more modular/flexible. These characteristics are the foundation of “resilience”‐based approaches (Linkov et al., 2014; National Research Council, 2012; Park et al., 2013; Woods, 2015).…”

Could the Last Interglacial Constrain Projections of Future Antarctic Ice Mass Loss and Sea‐Level Rise?

“…Ice-sheet models are computationally expensive to run at high resolutions necessary for sufficient accuracy. The number of simulations computationally tractable over a model's parameter space is therefore limited, making it difficult to construct an ensemble large enough to perform comprehensive statistical analyses (which are necessary for robust probabilistic projections of sea-level rise and coastal risk, e.g., Kopp, DeConto, et al, 2017;D. J. Rasmussen et al, 2020).…”

“…Ice‐sheet models are computationally expensive to run at high resolutions necessary for sufficient accuracy. The number of simulations computationally tractable over a model's parameter space is therefore limited, making it difficult to construct an ensemble large enough to perform comprehensive statistical analyses (which are necessary for robust probabilistic projections of sea‐level rise and coastal risk, e.g., Kopp, DeConto, et al, 2017; D. J. Rasmussen et al, 2020). In this study we develop a statistical “emulator” designed to mimic the behavior of the ice‐sheet model (the “simulator”) to fill intermediate solutions that have not been simulated over the ice‐sheet model parameter space (Bastos & O'Hagan, 2009; Kennedy & O'Hagan, 2001; C. E. Rasmussen & Williams, 2006).…”

The political complexity of coastal flood risk reduction: lessons for climate adaptation public works in the U.S.

“…For these reasons, knowing why projects fail is also useful not only for proponents but also for those who wish for a particular project to fail. Rather than thinking of protection strategies that focus on a single, critical threshold (e.g., the 100-year flood; Rasmussen et al, 2020), a more diverse suite could be used, such as those that are redundant, "safe-to-fail" (Kim et al, 2017), more affordable, combine natural and built infrastructure (Sutton-Grier et al, 2015), and more modular/flexible. These characteristics are the foundation of "resilience"-based approaches (Linkov et al, 2014;National Research Council, 2012;Park et al, 2013;Woods, 2015).…”