29 November 2016

Allowances for Evolving Coastal Flood Risk under Uncertain Local Sea-Level Rise

Science

In this study we exploit the availability of probabilistic local SLR projections to improve coastal flood risk management through the provision of several different metrics related to the risk of floods. In a non-stationary climate leading to sea level rise the traditional approach of using a fixed estimate of — for example — the 100-year event does not account for the constantly moving baseline from which the storm surge develops, underestimating future risk significantly over the lifetime of assets. What we produce is actionable flood hazard information that can be used by stakeholders to inform flood risk management despite ambiguity in SLR projections. Our calculations of average annual design-life flood levels, instantaneous allowances and design-life allowances can be used in relation to asset-specific time frames even in the presence of deep uncertainty in SLR projections to satisfy project design standards and risk preferences. Because of the evolution of flood levels in a non-stationary climate, failing to do so can compromise standards of protection, even from short project delays or extended durations. The main concept developed in the paper is that of SLR allowances, and relates to the need of accounting for a vertical buffer to maintain the annual expected probability of occurrence (AEP) to a desired level (for example 1%) over the life time of an asset of interest in the presence of rising sea levels. We use computations of storm surge characteristics from observed records, and fully probabilistic SLR projections, accounting for the uncertainty in both components of the problem.

Impact

In this study we exploit the availability of probabilistic local SLR projections to improve coastal flood risk management through the provision of several different metrics related to the risk of floods. In a non-stationary climate leading to sea level rise the traditional approach of using a fixed estimate of — for example — the 100-year event does not account for the constantly moving baseline from which the storm surge develops, underestimating future risk significantly over the lifetime of assets. What we produce is actionable flood hazard information that can be used by stakeholders to inform flood risk management despite ambiguity in SLR projections. Our calculations of average annual design-life flood levels, instantaneous allowances and design-life allowances can be used in relation to asset-specific time frames even in the presence of deep uncertainty in SLR projections to satisfy project design standards and risk preferences. Because of the evolution of flood levels in a non-stationary climate, failing to do so can compromise standards of protection, even from short project delays or extended durations. The main concept developed in the paper is that of SLR allowances, and relates to the need of accounting for a vertical buffer to maintain the annual expected probability of occurrence (AEP) to a desired level (for example 1%) over the life time of an asset of interest in the presence of rising sea levels. We use computations of storm surge characteristics from observed records, and fully probabilistic SLR projections, accounting for the uncertainty in both components of the problem.

Summary

In this study we exploit the availability of probabilistic local SLR projections to improve coastal flood risk management through the provision of several different metrics related to the risk of floods. In a non-stationary climate leading to sea level rise the traditional approach of using a fixed estimate of — for example — the 100-year event does not account for the constantly moving baseline from which the storm surge develops, underestimating future risk significantly over the lifetime of assets. What we produce is actionable flood hazard information that can be used by stakeholders to inform flood risk management despite ambiguity in SLR projections. Our calculations of average annual design-life flood levels, instantaneous allowances and design-life allowances can be used in relation to asset-specific time frames even in the presence of deep uncertainty in SLR projections to satisfy project design standards and risk preferences. Because of the evolution of flood levels in a non-stationary climate, failing to do so can compromise standards of protection, even from short project delays or extended durations. The main concept developed in the paper is that of SLR allowances, and relates to the need of accounting for a vertical buffer to maintain the annual expected probability of occurrence (AEP) to a desired level (for example 1%) over the life time of an asset of interest in the presence of rising sea levels. We use computations of storm surge characteristics from observed records, and fully probabilistic SLR projections, accounting for the uncertainty in both components of the problem.

Contact
Claudia Tebaldi
National Center for Atmospheric Research (NCAR)
Publications
Buchanan, MK, RE Kopp, M Oppenheimer, and C Tebaldi.  2016.  "Allowances for Evolving Coastal Flood Risk under Uncertain Local Sea-Level Rise."  Climatic Change, doi:10.1007/s10584-016-1664-7..