Abstract
Changes to mean sea level and/or sea level extremes (e.g., storm surges) will lead to changes in coastal impacts. These changes represent a changing exposure or risk to our society. Here, we present 21st century sea-level projections for Norway largely based on the Fifth Assessment Report from the Intergovernmental Panel for Climate Change (IPCC AR5). An important component of past and present sea-level change in Norway is glacial isostatic adjustment. We therefore pay special attention to vertical land motion, which is constrained using new geodetic observations with improved spatial coverage and accuracies, and modelling work. Projected ensemble mean 21st century relative sea-level changes for Norway are, depending on location, from −0.10 to 0.30 m for emission scenario RCP2.6; 0.00 to 0.35 m for RCP 4.5; and 0.15 to 0.55 m for RCP8.5. For all RCPs, the projected ensemble mean indicates that the vast majority of the Norwegian coast will experience a rise in sea level. Norway’s official return heights for extreme sea levels are estimated using the average conditional exceedance rate (ACER) method. We adapt an approach for calculating sea level allowances for use with the ACER method. All the allowances calculated give values above the projected ensemble mean Relative Sea Level (RSL) rise, i.e., to preserve the likelihood of flooding from extreme sea levels, a height increase above the most likely RSL rise should be used in planning. We also show that the likelihood of exceeding present-day return heights will dramatically increase with sea-level rise.
Highlights
In the global setting, Norway is commonly perceived as being at low risk from sea-level rise
By using the observed vertical land motion in our sea-level projections, we assume that the observed rates will persist unchanged over the 21st century. We argue that this is a reasonable assumption as GIA dominates present-day vertical land motion in Norway (e.g., [1,2,28,39,49]) and that the viscoelastic response time of the Earth is so long we would not expect any significant changes in the uplift rates over ~100 years
Our full GIA solution, as a contribution to Relative Sea Level (RSL) change, is the vertical land motion (VLM) field determined from least-squares collocation added to the modelled gravitational effects on sea level associated with GIA
Summary
Norway is commonly perceived as being at low risk from sea-level rise. It is well recognized that this uplift process will act to mitigate future sea-level rise (e.g., [3]) These factors suggest that, in comparison to other coastal countries, Norway has a generally low physical vulnerability to increasing sea levels [4]. Previous vulnerability assessments have helped identify the low-lying coastal areas of Norway that are at risk from sea-level rise owing to their important cultural and economic value [4,5]. These studies have shown that, in some specific areas where economic activities are concentrated close to the coast (e.g., oil, fishing and shipping industries), the impacts of sea-level rise could be significant
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