Rising sea levels triggered by global warming are already a matter of concern in the worldwide climate change campaign, with flooding causing havoc for coastal populations.

Melting glaciers and warming oceans, both triggered by increasing global temperatures, are the primary factors that cause sea levels to rise. While the annual sea level rise (SLR) is currently happening at a rate of about 3.2mm, this could go up to even 2.44 metres by 2100.

Though radar-based land elevation models suggest that a rising SLR will only have limited impact on the areas below mean sea level during the initial stages, a new study reveals the opposite – that the greatest increase in coastal area below mean sea level will occur in the early stages of SLR.

Published in American Geophysical Union’s Earth’s Future, the study led by Dutch researcher Ronald Vernimmen applied new and more accurate satellite LiDAR elevation data to conclude that in a third of the countries, inundation will be caused by the first metre of SLR and in nearly all, within the first two metres. This also means that in many regions the time available for coastal communities to prepare for increased exposure to flooding may be considerably lesser than previously assumed. After the first few metres of sea level rise, the rate at which land area falls below mean sea level decreases, the study revealed.

The study used high-resolution measurements of land elevation from NASA’s ICESat-2 LiDAR satellite to improve upon models of sea level rise and inundation.

Recommending the use of LiDAR data in SLR impact assessments, the researchers noted that calculations using radar-based global elevation models available to date have generally underestimated the extent of lowest coastal areas that are most exposed to sea level rise (SLR).

“Radar is unable to fully penetrate vegetation and, therefore, overestimates surface elevation,” said Vernimmen, a researcher at the Dutch research firm Data for Sustainability, who works on flood protection and spatial planning advisory projects.

Analysing the new LiDAR-based elevation model, Vernimmen and co-author Aljosja Hooijer found that two metres of SLR would cover up to 2.4 times the land area observed by the older radar-based elevation models.

For example, the LiDAR data suggests that a 2-metre increase in sea level could put most of Bangkok and its 10 million residents below sea level; based on older data, Bangkok would still be largely above mean sea level under that same amount of sea level rise. Globally, such an increase would push 240 million more people to live below mean sea level. After 3 and 4 metres, that number increases by 140 million and 116 million, respectively.

While levees, dykes and pumping stations can protect some cities from submerging due to rising sea levels – as seen in Amsterdam and New Orleans – such protection measures can be expensive and take decades to implement, says Vernimmen.

“If vulnerable communities want to mitigate the most damage, they need to act before the sea rises those first few metres,” he added.

Source: American Geophysical Union (AGU)

Image credit: grumpylumixuser/Wikimedia Commons

Architecture & Design Team

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