A new study by Dutch researchers has found that the amount of land covered by the first 2m of sea-level rise is likely to be more than twice as much as older elevation models predicted.
Current models of sea-level rise suggest the most widespread impacts will occur after the sea level has risen by several meters. But a new study finds the biggest increases in inundation will occur after the first 2m of sea-level rise.
The study used high-resolution measurements of land elevation from NASA’s ICESat-2 lidar satellite, launched in 2018, to improve models of sea-level rise and inundation. Previous assessments typically relied on radar-based data, which are less precise.
Ronald Vernimmen, a researcher at Data for Sustainability, said, “Radar is unable to fully penetrate vegetation and therefore overestimates surface elevation. Many coastal areas are lower than scientists thought they were.”
The underestimates of land elevation mean coastal communities have less time to prepare for sea-level rise than expected, with the biggest impacts of rising seas occurring earlier than previously thought. After those first few meters of sea-level rise, the rate at which land area falls below mean sea level decreases.
Vernimmen, who works on flood protection and spatial planning advisory projects, started using these more accurate measurements of land elevation when he realized that existing land elevation estimates were not suitable for quantifying coastal flooding risk.
Using the new measurements of land elevation, Vernimmen and co-author Aljosja Hooijer found coastal areas lie much lower than older radar data suggested. Analyses of the new lidar-based elevation model revealed that 2m of sea-level rise would cover up to 2.4 times the land area as observed by radar-based elevation models.
For example, the lidar data suggests that a 2m increase in sea level could put most of Bangkok and its 10,000,000 residents below sea level, while older data suggested that Bangkok would still be largely above mean sea level under that same amount of sea-level rise. In total, after 2m of sea-level rise, Vernimmen and Hooijer estimate that 240,000,000 more people will live below mean sea level. After 3m and 4m of sea-level rise, that number increases by 140,000,000 and by another 116,000,000, respectively.
Cities below future sea level may not necessarily be submerged because levees, dikes and pumping stations can protect some areas from rising seas; Amsterdam and New Orleans are modern examples of this. However, such protection measures can be expensive and take decades to implement. If vulnerable communities want to mitigate the most damage, they need to act before the sea rises those first few meters, according to Vernimmen.
To view the complete study published in the AGU journal Earth’s Future, click here.