Summary/Abstract
The latest projections indicate that sea-level rise (SLR) is certain to exceed 2 m in coming centuries, and a rise by 4 m is considered possible. Radar-based land elevation models applied to date suggest that the increase of area below mean sea level, that is potentially exposed to permanent flooding, will accelerate as SLR proceeds, being relatively limited initially. However, applying new and more accurate satellite LiDAR elevation data the authors find the opposite pattern, with the fastest increase in the area of exposed land occurring in the early stages of SLR. In one-third of countries most of this increase will be caused by the first meter of SLR and in nearly all within the first 2 m. We conclude that in many regions the time available to prepare for increased exposure to flooding may be considerably less than assumed to date, and that better elevation data will support timely preparations. The global LiDAR lowland DTM (GLL_DTM_v2) elevation data set developed for this assessment is available in the public domain.