Global airport operators, faced with rising sea levels and more powerful storms as the climate changes, are starting to invest in measures including higher runways, seawalls and better drainage systems to future-proof immovable assets.

In early September, a seawall at Japan’s Kansai International Airport built on a reclaimed island near Osaka, was breached during Typhoon Jebi.

The runway was flooded and it took 17 days to fully restore airport operations, at a high cost to the region’s economy as well as the dozens of airlines that canceled flights.

Major airports in Hong Kong, mainland China and North Carolina were also closed due to tropical storms last month.

Such incidents highlight the disaster risks to investors and insurers exposed to a sector with an estimated $262 billion of projects under construction globally, according to Fitch Solutions.

“There is a kind of one-way direction with regards to the frequency and severity of climate change-related events,” said Fitch Solutions Head of Infrastructure Richard Marshall. “If people aren’t taking that seriously, that is a risk.”

Fifteen of the 50 most heavily trafficked airports globally are at an elevation of less than 30 feet above sea level, making them particularly vulnerable to a changing climate, including rising sea levels and associated higher storm surges.

“You see it at individual airports that are already seeing sea rise and are already dealing with water on their runway,” Airports Council International (ACI) Director General Angela Gittens said, citing examples in island nations including Vanuatu and the Maldives.

“But even in some of these mature economies they are having more storms, they are having to do more pumping. My old airport in Miami is in that scenario.”

A draft copy of an ACI policy paper reviewed by Reuters and due to be released this week warns of the rising risks to facilities from climate change. It encourages member airports to conduct risk assessments, develop mitigation measures and take it into account in future master plans.

The paper cites examples of forward-thinking airports that have taken climate change into account in planning, such as the $12 billion Istanbul Grand Airport on the Black Sea, set to become one of the world’s largest airports when it opens next month.

Investor Interest

Debt investors in particular have high exposure to airports, most of which are owned by governments or pension funds. Ratings agency Moody’s alone has $174 billion of airport bonds under coverage.

Earl Heffintrayer, the lead analyst covering U.S. airports at Moody’s, said the risk of climate change became apparent to investors after Superstorm Sandy closed major New York airports for days in 2012.

Sandy led to the cancellation of nearly 17,000 flights, costing airlines $500 million in revenues and disrupting operations around the world, according to a 2017 presentation by Eurocontrol on climate change risk.

Investors are increasingly asking about mitigation plans at low-lying airports like San Francisco and Boston as they look to invest in bonds with terms of up to 30 years, Heffintrayer said.

San Francisco International Airport, built on reclaimed land that is slowly sinking, has completed a feasibility study on a $383 million project to make the airport more resilient to sea level rises on its 8 miles (12.9 km) of bay front shoreline by 2025.

“We are seeing a lot more thought going into protection against flood damage, catastrophe, making sure that the storm drains around the airport are fit for purpose,” said Gary Moran, head of Asia aviation at insurance broker Aon. “There definitely is a lot more thought going into potential further worsening in weather conditions further down the line.”

Taking Action

Singapore’s Changi Airport, which has analyzed scenarios out to 2100, has resurfaced its runways to provide for better drainage and is building a new terminal at a higher 18 feet (5.5 meters) above sea level to protect against rising seas.

Moran said such steps were prudent and would provide comfort to insurers.

“If you were to look at Singapore, if something was to happen at Changi in terms of weather-related risk, Singapore would have a problem,” he said. “There isn’t really too much of an alternative.”

Singapore expects sea levels to rise by 2.5 feet (0.76 meter) by 2100. Changi Airport declined to comment on the cost of the extra protection.

ACI, Fitch, Moody’s and Standard & Poor’s were unable to provide Reuters with an estimate of the global cost of climate change protection at airports. The protective action is often folded into larger refurbishment and expansion projects, ratings agency analysts said.

In Australia, Brisbane Airport and located on reclaimed land on the coast at just 13 feet (4 meters) above sea level, is constructing a new runway 3.3 feet (1 meter) higher than it otherwise would have done, with a higher seawall and better drainage systems as sea levels rise.

Paul Coughlan, the director of Brisbane Airport’s new runway project, said the incremental cost of such moves was relatively low – for example the seawall cost around A$5 million ($3.6 million) more than without taking into account sea level rises – but the potential benefits were big.

“At the end of the day, whether you are a believer in climate change or a disbeliever, doing a design that accounts for elevated sea levels, more intense rainfall, flooding considerations, that is just prudent,” Coughlan said.

“If you build it into your design philosophy from day one, you don’t pay that much of a premium and you have bought a lot of safeguards.” ($1 = 1.3841 Australian dollars)