Towards a global regionally varying allowance for sea-level rise

Allowances have been developed for future rise of relative sea-level (i.e. sea level relative to the land) based on the projections of regional sea-level rise, its uncertainty, and the statistics of tides and storm surges (storm tides). An ‘allowance’ is, in this case, the vertical distance that an asset needs to be raised under a rising sea level, so that the present likelihood of flooding does not increase. This continues the work of Hunter (2012), which presented allowances based on global-average sea level and local storm tides. The inclusion of regional variations of sea-level rise (and its uncertainty) significantly increases the global spread of allowances. For the period 1990–2100 and the A1FI emission scenario (which the world is broadly following at present), these range from negative allowances caused by land uplift (in the northern regions of North America and Europe) to the upper 5-percentile which is greater than about 1 m (e.g. on the eastern coastline of North America).