Climate-induced sea-level rise to worsen tsunami impacts

In the wake of the latest tsunami to hit the Indonesian coast, research shows how even slight sea-level rises linked to climate change could significantly increase the devastating effects of tidal waves.

Following the extreme, earthquake-triggered tsunamis unleashed in the Indian Ocean in 2004 and Japan in 2011, a spate of disaster films like The Impossible have depicted doomsday tidal wave scenarios.

Nature and Environment | 02.10.2018

Such fear of "big water," in US President Donald Trump's parlance, was revived this week in the wake of the tsunami that has so far killed around 1,350 people in Indonesia.

Yet just weeks before this latest disaster, a group of scientists predicted that tsunami impacts will indeed worsen due to sea-level rises related to climate change. 

"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, associate professor in the Department of Geosciences at Virginia Tech told DW.

Read moreIndonesia quake: 'Tsunami warning system needs improvement'

Weiss was one of several authors of a study published in Science Advances last month that, somewhat presciently, looked at tsunami impacts in a world of rising seas.

Titled "A modest 0.5-meter (1.5-foot) rise in sea-level will double the tsunami hazard in Macau," the study was also co-authored by Adam Switzer, associate professor at Singapore's Earth Observatory.

"The tsunami like the one that occurred in Palu on Friday — that event in 50 years time may have been worse because sea levels are rising in that part of the world, and it's a very low-lying plain and it's likely to have started to experience increased flooding," Switzer told DW.

Indonesia tsunami and earthquake devastate Sulawesi island

A bridge washed away

On Friday, September 28, a massive tidal wave unleashed by a 7.5-magnitude quake slammed into the Indonesian city of Palu located on Sulawesi island. The impact washed away Palu's 300-meter (328 yard) double-arched bridge, plunging cars into the water.

Indonesia tsunami and earthquake devastate Sulawesi island

A deadly geophysical coincidence

This satellite image from October 1 shows how Palu is built on lowlands at the end of a narrow bay. Scientists say the shape of the bay amplified the size and power of the waves by forcing the water into a narrow and shallow channel. The earthquake's epicenter was also located close to shore, making the waves more powerful and leaving little time for warning.

Indonesia tsunami and earthquake devastate Sulawesi island

A flooded mosque

The wave hit Palu, a city with a population of 380,000, on Friday evening as Muslim worshippers were gathering for evening prayers in local mosques. Authorities said that many others were caught on the beach while preparing a festival which was set to start later in the day.

Indonesia tsunami and earthquake devastate Sulawesi island

Hospitals overwhelmed

With local hospitals crowded by hundreds of wounded, doctors were forced to treat the injured outside. Komang Adi Sujendra, director of a Palu hospital, urged assistance. "We need all the help we can get," he said. "We need field hospitals, medical workers, medicines and blankets."

Indonesia tsunami and earthquake devastate Sulawesi island

Burying the dead

On October 2, the official death toll of the tsunami and quake reached over 1,200. Authorities expect that number to rise as more people remain trapped. On October 1, the national disaster agency told AP that over 150 bodies were buried in a mass grave, with the burial operations ongoing. Indonesia is a majority-Muslim nation, and religious custom calls for burial soon after death.

Indonesia tsunami and earthquake devastate Sulawesi island

Trapped below the rubble

The tsunami carried sand, mud and debris inland. Roads were blocked and communications disrupted with other cities. Rescue efforts in remote areas around Palu was hampered by the extent of damage to infrastructure. More heavy equipment was also needed.

Indonesia tsunami and earthquake devastate Sulawesi island

'Liquified' earth

The heavy earthquake caused sand and silt saturated by water to take on liquid characteristics in a process known as liquefaction. The national rescue agency said that over 1,700 houses in the Palu area were wiped out by liquefied soil.

Indonesia tsunami and earthquake devastate Sulawesi island

President Widodo pledges to rebuild

Authorities managed to open the local airport a day after the tsunami, allowing the Indonesian mlitary to start delivering aid. The country's President Joko Widodo (r) visited the island and pledged to rebuild the city. The Associated Press reported that Widodo has authorized international help. The EU and 10 countries including the US, Australia and China have offered assistance.

Indonesia tsunami and earthquake devastate Sulawesi island

Looters risk life and limb

Indonesian media showed images of survivors entering the heavily damaged malls and supermarkets to loot supplies, despite the risk of building collapse. Some Palu residents started returning to their homes to salvage usable items. German news agency dpa reported on October 2 that police arrested 45 people in Palu for looting.

Indonesia tsunami and earthquake devastate Sulawesi island

Queuing for fuel

The earthquake and tsunami knocked out power to the island and left many residents without access to clean water and medical supplies. Some of them descended on gas stations to pump out fuel by hand for their generators.

Indonesia tsunami and earthquake devastate Sulawesi island

Foreign aid

President Widodo has opened the door to foreign aid organizations as 200,000 people remain in desperate need of food, water and medicine. International Search and Rescue (ISAR) Germany has sent personnel to assist authorities.

Indonesia tsunami and earthquake devastate Sulawesi island

Search called off

On October 11, authorities called off the search for missing people, leaving the whereabouts of around 5,000 people a mystery. Experts believe that many of the missing are buried underground after entire villages were swallowed by "liquid earth." To commemorate the missing, parks and monuments are planned for Balaroa, Petobo and Jono Oge, considered the worst-hit areas of the island.

Climate connection

Scientists long assumed that tsunamis and rising sea levels were completely separate phenomena. Despite monitoring how rising sea levels will cause coastal communities to be inundated in storm surge conditions — especially in low-lying island nations like the Solomon Islands — few have tried to understand how this climate change symptom could exacerbate extreme weather and natural disasters.

"We really want to look at the extremes," said Switzer, "at the worse case scenarios." Using cutting-edge computer modeling which, according to Weiss, wasn't available five years ago, this latest research looks at tsunami impacts at extreme high and king tides.

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In this vein, coastal cities like Macau in China that are currently regarded as "tsunami safe," won't be in the future if sea-level rise predictions hold.

"Areas that are considered tsunami-safe and require a 2- to 3-meter tsunami for flooding, will only require a 1.5- to 2-meter tsunami," Switzer said.

Read more: Will extreme weather become even deadlier?

Worst-case scenario

The problem will be further exacerbated since sea-level rises are now predicted to be much higher than previously expected. "What we thought was the absolute worst case five or 10 years ago, is just a medium prediction today," Weiss said. 

Greater sea-level rises mean small tsunamis, which happen more frequently, will also be more destructive.

According to Weiss, smaller earthquake and tsunamis are much more frequent than the kind of massive event that caused the 2011 Tohoku tsunami in Japan. Thus, the tsunami triggered by that 9.1-magnitude quake could be created by smaller tremors in a world of rising seas.

Read moreJapan marks 7th anniversary of tsunami and Fukushima nuclear disaster

An area affected by 'liquefaction' of the earth following the tsunami in Palu, Indonesia, which caused all structures to collapse. Authorities fear hundreds of people are still buried here

Today, it would take an 8.6-magnitude quake to flood Macau, but in 50 years time, climate-induced sea-level rises mean an 8.2 quake, which is six times less powerful, would inundate the city.

Like the typical disaster wave film scenario, where massive walls of water wipe out high-rise coastal cities, Macau is the kind of Asian megacity built on reclaimed lowland that will be most vulnerable in a warmer world.   

Read moreMother Nature fights back: Natural disasters in cinema 

US and Europe also vulnerable

With rising sea levels, coastal cities could be increasingly vulnerable to tsunamis originating in distant climes. This is partly because tsunamis can travel over large areas. The 2011 Tohoku mega-tsunami traveled from Japan to California in just 10 hours, at a speed of 700 kilometers (435 miles) per hour, according to Weiss. 

The Virginia Tech-based researcher, who hails from Germany, is also employing his computer modeling to look at how a future tsunami could impact California following an earthquake in Alaska, for example; or how the Atlantic coast could be inundated due to huge tsunamis unleashed by the Greenland tectonic plate. 

Tidal waves of eight to 10 meters could also hit the French coast in the latter scenario, according to Weiss. 

Read moreGreenland iceberg could cause tsunami, authorities warn Innaarsuit Island

The 'tide of the century' hits the French coast in 2015. The intensity of these tides will also increase as sea levels rise

Mitigating tsunami impacts

Much of this research will contribute to building appropriate coastal defense systems to better protect cities and communities from cyclones and major flooding. But such measures will have little effect if sea-level rises double, triple or even quadruple the frequency and impact of tsunamis.

As such, the ultimate defense against this doomsday scenario will be climate change mitigation.

"Sea-level rise is primarily driven by our use of fossil fuels and our continuous production of carbon dioxide," said Switzer. "You can't decouple these things, they're all linked."