Faleolo International Airport will need extra drainage to deal with heavy rainfall as a result of climate change, a Japanese study has found.

The refurbished airport, which opened in 2016, faced severe flooding in late 2020, and research published this month warns there may be many more similar floods in the future.

The study from the Department of Civil Engineering at the University of Tokyo studied parts of the airport at such high risk of severe flooding that three hours of serious rain could inundate the runway and send water towards the sea in just three hours. 

After six hours of heavy rain, the study suggests, two water collection areas could still be inundated with water.

A separate drainage network must be constructed for each of those three catchment areas, the report, published in the Journal of Disaster Research, says.

“The combination of sea-level rise and the sea level anomaly induced by stormy waves on the fringing reef could have non-negligible impacts on the drainage system,” the paper said.

The paper was a case study into how Faleolo International Airport can teach not only Samoa but other island countries how to manage the potential risks of flooding, which grow each year because of climate change.

“A cost-effective drainage strategy is necessary to protect flood-prone areas because the financial budget is usually limited in these island countries.

“As a case study, this paper aims to investigate the flooding hazard in Faleolo International Airport (FIA), Samoa, and to explore the efficient drainage strategy under future rainfall scenarios. 

Based on its calculations of how much rainfall would cause different levels of flooding to the airport, the researchers recommend the airport needs a drainage upgrade.

They calculate that if upgraded in the way their paper describes, new pipes would certainly reduce the depth of the flooding waters.

They also factor in potential sea-level rises, stormy waves, and sea surges, which should be factored into how the new drainage system is designed, they say.

“Little difference was observed in the drainage performance if the sea level difference was within the range of astronomical tide. 

“Non-negligible influence, however, was observed if the water level was raised to 3 m, which could likely occur under the scenario of sea-level rise and sea level anomaly due to stormy waves.”

The new system will need multiple pipes, not one or two, to deal with the potential water levels of a flood.

“Multiple drainage pipes, therefore, may have a better effect on efficient drainage for flood prevention,” the paper states.

“Besides width, increases in the number of pipes also showed a clear effect of reducing inundation. The location of the drainage pipes plays an important role in effectively reducing the flooding risk.

“Using a larger number of drainage pipes is not always the optimum strategy for flooding mitigation. Torrential rainfall with significantly high intensity introduces much uncertainty and raises difficulties for the development of drainage strategy.”

The research was supported by Japan’s Ministry of Environment, which undertook research into the impact of climate change on coastal hazards in the South Pacific Islands.