Studies Reveal Underestimated Sea Levels and Faster Coastal Subsidence

Recent studies have highlighted discrepancies in sea level measurements and land subsidence rates, affecting coastal vulnerability assessments. A study by geographers at Wageningen University & Research in the Netherlands analyzed tidal gauge data from 385 locations. The research found that actual sea levels are on average nearly 1 foot higher than estimates based on global models.

These models often assume calm seas and overlook factors like ocean currents and winds. In many cases, previous sea level estimates were 3 feet or more too low. As a result, approximately 80 million people live in coastal areas below current sea levels, nearly double prior estimates.

This increases the number of individuals at risk from accelerating sea level rise in the coming decades.

Subsidence in River

Deltas Another study examined subsidence in 40 major river deltas using satellite radar data.

The research, conducted by an Earth system scientist at the University of California, Irvine, produced 3D maps showing subsidence in more than half of these deltas. In 18 deltas, subsidence rates exceed those of sea level rise, effectively doubling or multiplying the local relative sea level increase.

Affected areas include the deltas of the Nile in Egypt, the Mekong in Vietnam, the Mahanadi in India, and the Yellow River in China.

If current subsidence rates continue, these regions could flood sooner than previously forecasted. The study provides consistent, high-resolution data on subsidence, improving on earlier inconsistent estimates.

Implications for Research and Policy Both

studies indicate that past research has underestimated coastal risks due to faulty methodologies in sea level modeling.

More than 90 percent of local studies rely on mathematical models of the Earth's shape that do not account for real-world variations. Researchers stated that forecasts for flooding in low-lying areas may be off by decades, urging more urgent planning. Additional investigations are needed for other coastal regions not covered in these studies.

K. Met Office’s Hadley Centre for Climate Science said the impacts of sea level rise under climate change have been systematically underestimated. An oceanographer at the University of Cape Town stated that the studies together present a more concerning picture of coastal vulnerability.