New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding

TLDR

Most estimates of global mean sea‑level rise this century are below 2 m, comparable to the positive vertical bias of NASA’s SRTM digital elevation model used to assess population exposure to extreme coastal water levels. The study aims to estimate how many people currently occupy land less than 10 m above present high‑tide lines, including those below 1 m, to improve vulnerability assessments. CoastalDEM, a neural‑network‑based digital elevation model, reduces SRTM error to provide more accurate elevation data. Using CoastalDEM, the authors find that the number of people living on land below projected 2100 high‑tide lines more than triples SRTM estimates—about 190 M under low emissions (up from 110 M today), up to 630 M under.

Abstract

Most estimates of global mean sea-level rise this century fall below 2 m. This quantity is comparable to the positive vertical bias of the principle digital elevation model (DEM) used to assess global and national population exposures to extreme coastal water levels, NASA’s SRTM. CoastalDEM is a new DEM utilizing neural networks to reduce SRTM error. Here we show – employing CoastalDEM—that 190 M people (150–250 M, 90% CI) currently occupy global land below projected high tide lines for 2100 under low carbon emissions, up from 110 M today, for a median increase of 80 M. These figures triple SRTM-based values. Under high emissions, CoastalDEM indicates up to 630 M people live on land below projected annual flood levels for 2100, and up to 340 M for mid-century, versus roughly 250 M at present. We estimate one billion people now occupy land less than 10 m above current high tide lines, including 230 M below 1 m. Accurate estimates of global mean sea-level rise are important. Here the authors employ a new digital elevation model (DEM) utilizing neural networks and show that the new DEM more than triples the NASA SRTM-based estimates of current global population occupying land below projected sea levels in 2100, with more than 200 million people could be affected based on RCP4.5 and 2 degC of warming.