According to a new study, even a minor increase in sea level rise could cause a higher risk of tsunami damage worldwide.
Researchers from Virginia Tech University, as well as others, found that even a one-foot increase in sea level would likely increase flooding further inland from tsunamis following earthquakes in coastal communities.
“Our research shows that sea-level rise can significantly increase the tsunami hazard, which means that smaller tsunamis in the future can have the same adverse impacts as big tsunamis would today,” Robert Weiss, an associate professor in the Department of Geosciences at Virginia Tech, said in a statement.
According to Weiss, smaller tsunamis generated by earthquakes with smaller magnitudes occur frequently and regularly around the world.
The researchers mapped out computer-simulated tsunamis at both current sea level conditions, as well as at increases of 1.5 feet and three feet for Macau, a low-lying territory in South China on the northern coast of the South China Sea. Macau is considered the most densely populated region in the world, with a population of 650,900 in just 11.8 square miles. However, it also is considered relatively safe from current tsunami risks.
Current projections have sea levels in Macau rising by 1.5 feet by 2060 and three feet by 2100.
The researchers developed probabilistic tsunami inundation maps based on a 100,000-year synthetic earthquake catalog at the Manila megathrust. They used the Cornell Multi-grid Coupled Tsunami Model (COMCOT) to simulate the tsunami inundation process for all tsunamigenic earthquake events with a moment magnitude greater than or equal to 8.0 in the synthetic catalog.
“We produced a series of tsunami inundation maps for Macau using more than 5,000 tsunami simulations generated from synthetic earthquakes prepared for the Manila Trench,” Adam Switzer, an associate professor at the Earth Observatory of Singapore, said in a statement.
The researchers found that at current levels, an earthquake would need to tip past an 8.8 magnitude to cause widespread tsunami inundation in Macau. However, the region saw a dramatic hazard increase with an increase in sea level rise.
“We found that the increased inundation frequency was contributed by earthquakes of smaller magnitudes, which posed no threat at current sea level, but could cause significant inundation at higher sea-level conditions,” Lin Lin Li, a senior research fellow, said in a statement.
When the researchers forecasted a 1.5 foot increase the tsunami-induced flooding rose 1.2 to 2.4 times current levels, and when they plugged in a three foot sea level rise, that increased the flooding by 1.5 to 4.7 times.
The hazard of large tsunamis in the South China Sea region primarily comes from the Manila Trench, a megathrust system that stretches from offshore Luzon in the Philippines to southern Taiwan.
While the Manila Trench megathrust has not seen an earthquake with a magnitude larger than 7.8 since the 1560s, the researchers believe the region shares several similarities to other areas hit recently by earthquakes including the 2004 Sumatra-Andaman earthquake and the 2011 earthquake in northern Japan.
“The South China Sea is an excellent starting point for such a study because it is an ocean with rapid sea-level rise and also the location of many mega cities with significant worldwide consequences if impacted,” Weiss said. “The study is the first if its kind on the level of detail and many will follow our example.
“Sea-level rise needs to be taken into account for planning purposes, for example for reclamation efforts but also for designing protective measures, such as seawalls or green infrastructure,” he added. “What we assumed to be the absolute worst case a few years ago now appears to be modest for what is predicted in some locations. We need to study local sea-level change more comprehensively in order to create better predictive models that help to make investments in infrastructure that are or near sustainable.”
The study was published in Environmental Studies.