Science News - October 30, 2019

Sea level rise this century could flood coastal areas that are now home to 340 million to 480 million people, researchers from Climate Central, a research and advocacy group, report. That’s roughly triple the number of people estimated to be at risk using previous coastal elevation data.

The new estimate, published October 29 in Nature Communications, comes from efforts to refine NASA satellite elevation data, and it illustrates the implications of elevation data having been overestimated in some places by up to 5 to 10 meters. The results are presented in terms of how many people, by today’s population numbers, could be affected, but don’t predict how many people will actually be living in those coastal areas in 2100.

“The global threat from sea level rise and coastal flooding is far greater than what we thought it was,” says Benjamin Strauss, who heads Climate Central in Princeton, N.J.

While the research highlights an increased threat to people currently living in coastal areas, it does not estimate how much more land area will fall below flood projection lines, and whether that area includes a handful of coastal megacities or mostly large swaths of less populated land. So it’s unclear how many people in future cities might be at risk of inundation, which could limit the usefulness of the findings to city managers. The researchers say those details fell outside the scope of this study.

Still, the new estimate attempts to correct a large margin of error found in previous estimates of global coastal elevations. Those estimates are based on NASA’s Shuttle Radar Topography Mission, or SRTM, which created a global topographic map from satellite images and radar data. SRTM measures elevation by bouncing radar signals off Earth’s surface — whether that’s a tree, a building or the land itself. So the method can overestimate elevation levels, especially in forests and cities.

“If we’re overestimating elevations [in coastal cities], we’re getting a very over-optimistic view of the impact of flooding,” says Ashton Shortridge, a geographer at Michigan State University in East Lansing who was not involved in the study. ...
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