Kansai International Airport sits on its own island in Osaka Bay, almost 5 km off the coast of Japan, a gateway for millions of international tourists who go on pilgrimage to the historic sites of Kyoto and Nara.

Serving 80,000 passengers a day, the airport was built on land reclaimed from the sea to minimize noise pollution and protests over land rights, and designed to withstand storm surges sending seawater 2.7 metres high.

But when Typhoon Jebi hit in September, high waves swept over the walls protecting the airport from the sea, flooding a runway and Terminal 1. Adding to the chaos, some 3,000 passengers were stranded overnight when a tanker crashed into the only bridge that links the airport to the mainland.

 Kansai International Airport was flooded when Typhoon Jebi crashed ashore.
Image: Kyodo/via REUTERS

Kansai is not the only airport to have flooded this year. Flooding is becoming a worrying trend.

Some of the world’s busiest airports were built close to sea level - and to the sea - without climate change in mind, and are now vulnerable.

What’s the scale of the problem?

Twenty-five percent of the world’s 100 busiest airports are less than 10 metres above sea level, according to data from the Airports Council International and OpenFlights. This puts them at serious risk of flooding during storms, caused in part by a rise in sea level.

As global warming causes the polar ice sheets to melt, the sea level rises, which in turn leads to more frequent and intense storm surges, according to The Royal Society, the UK’s fellowship of scientists. Since 1901, global sea level has risen by 20 cm, and according to The Royal Society, if carbon dioxide and other greenhouse gases continue to be emitted at their current rate, it may rise by a further 0.5 to 1 metres by 2100.

 Global sea level has risen by 20 cm since the late 19th century.
Image: Shum and Kuo (2011)/Royal Society

Vulnerable airports

Cochin International Airport in Kerala, India, closed for almost two weeks in August due to flooding, after the Periyar River burst its banks in the heaviest rain to hit the state since the 1920s. The floods submerged a runway and damaged 2.6 km of perimeter wall.

Ironically, in July, the country’s seventh busiest airport was awarded the UN’s highest environmental honour, the Champion of the Earth Prize, for being the world’s first airport to function entirely on solar power.

Also in August, Hurricane Lane brought record heavy rain to Hawaii. Hilo International Airport reported its wettest four-day period ever, with over 93 cm of rain between August 22 and 25. Video footage showed sandbags and roped off sections in the terminal building.

New York was crippled for days in 2012 when Hurricane Sandy caused flooding of all three of the city’s airports - LaGuardia, Newark and JFK.

“We know that there are going to be impacts. And we expect those impacts to become serious,” Michael Rossell, deputy director-general at Airports Council International, told the New York Times. “Recognizing the problem is the first step, and recognizing the severity is the second. The third is: What can we do about it?”

 New York’s LaGuardia Airport after Hurricane Sandy in 2012.
Image: REUTERS/U.S. Coast Guard/Handout

Adapting to rising seas

Engineers are beginning to restructure airports so that they can withstand flooding, and future airports will need to be built on higher land.

In the US, New York’s LaGuardia Airport received a $28 million grant in 2015 to build a flood wall, pumps to remove rainwater and improved drainage for the runways. Meanwhile Minnesota’s St Paul Downtown Airport now has a 2.4-metre removable wall to protect runways from being flooded by the Mississippi.

Norway is planning to build all airports in future at least 7 metres above sea level and Hong Kong International’s third runway will include 13.4 km of seawall to protect it from storm surges and flooding.