A tsunami threat is facing major cities along or near the Mediterranean Sea, the UN has warned.

There is an almost 100 percent chance that a wave over 1-meter tall will reach these cities in the next 30 years, said the UN Educational, Scientific and Cultural Organization.

It added that the risk is rising in line with sea levels, and that while countries in the Pacific and Indian Ocean are conscious of the threat, Mediterranean coastal regions are not. 

A 2018 study found that rising sea levels added to tsunami risk as they allow waves to travel farther. 

UNESCO said five at-risk Mediterranean communities, including Alexandria in Egypt and Turkey’s largest city Istanbul, will join a 40-strong “tsunami-ready” list of towns and cities.

The “tsunami-ready” program, which covers 21 countries, is part of the UN’s efforts to ensure that threatened communities are prepared.

“The tsunamis of 2004 and 2011 were a wake-up call,” said Bernardo Aliaga, lead tsunami expert at UNESCO, referring to the Indian Ocean and Japanese tsunamis that killed 230,000 and 13,000 people, respectively.

“We have come a long way since 2004. We are safer today. But there are gaps in preparedness and we need to improve; we need to make sure warnings are understood by visitors and communities.”

Since 2004, the UN’s Pacific Tsunami Warning Centre has reacted to some 125 tsunami events. It has established 12 new warning centers, including one in Turkey.

“The risk of tsunami is underestimated in most areas, including the Mediterranean,” Aliaga said. “Events are not very frequent and the risk does not translate from one generation to another.”

He added: “We need to get the message out. In the Mediterranean, there is no question about it: it is not if, it’s when.”

But while these centers go a long way to prepare communities, Aliaga told The Guardian: “The warning is not the full story, the second part is community preparedness — how people behave and react. That has a way to go.”

Authorities in Alexandria, Istanbul and other Mediterranean cities have been preparing “tsunami-ready” policies that include new evacuation signage and techniques.

As many of these cities are popular tourism destinations, education is also vital, said Aliaga. “We want 100% of communities, where there is a proven hazard, to be ready to respond by 2030,” he said.

“They will have evacuation maps, they will have carried out exercises and they will already have in place 24-hour alerts,” he added.

“If it’s a local tsunami, you have 20 minutes maximum before the first wave hits. The second wave is larger and comes 40 minutes after the first one. You still have the possibility of escape.”