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.
Last month, 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 and the dozens of airlines that cancelled flights.
Major airports in Hong Kong, mainland China and North Carolina in the United States 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 US$262 billion (S$359 billion) of projects under construction globally, according to Fitch Solutions. "There is a kind of one-way direction with regard 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 10m above sea level, making them particularly vulnerable to a changing climate, including rising sea levels and associated higher storm surges.
Singapore's Changi Airport, which has analysed scenarios out to 2100, has resurfaced its runways to provide for better drainage and is building a new terminal at a higher 5.5m above sea level to protect against rising seas.
"You see it at individual airports that are already seeing sea rise and are already dealing with water on their runways," Airports Council International (ACI) director-general Angela Gittens said, citing examples in island nations including Vanuatu and the Maldives.
A draft copy of an ACI policy paper 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 them into account in future masterplans.
The paper cites examples of forward-thinking airports that have taken climate change into account in planning, such as the US$12 billion Istanbul Grand Airport on the Black Sea, set to become one of the world's largest airports when it opens this month.
Debt investors in particular have high exposure to airports, most of which are owned by governments or pension funds. 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, said Mr Earl Heffintrayer, the lead analyst covering US airports at ratings agency Moody's.
San Francisco International Airport, built on reclaimed land that is slowly sinking, has completed a feasibility study on a US$383 million project to make it more resilient to sea-level rises on its 12.9km of bay-front shoreline by 2025.
Mr Gary Moran, head of Asia aviation at insurance broker Aon, said such steps were prudent.
"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 0.76m by 2100. Changi Airport declined to comment on the cost of the extra protection.