Coastal flooding caused by global warming could cost the global economy $1 trillion a year in coming decades and Vancouver is one of the cities most at risk for losses, says a new study.

The article, published Tuesday in the journal Nature Climate Change, is part of an ongoing project by the Organization for Economic Co-operation.

"This work shows that flood risk is rising in coastal cities globally due to a range of factors, including sea-level rise," Robert Nicholls, a professor of coastal engineering at the University of Southampton in the United Kingdom and co-author of the study, said in a news release.

"Hence, there is a pressing need to start planning how to manage flood risk now."

Nicholls told CBC News that Vancouver is on the list of vulnerable cities because of its large population living along the coastal flood plain.

"Historically your city has grown on a delta, and those areas tend to be naturally flood-prone," says Nicholls.

"Our study raises the flag that it would be wise for Vancouver to look carefully at this issue if it hasn't been looked at already and to start thinking about appropriateness of current responses and whether you need to do more."

Vancouver at risk

The University of Southampton team looked at population, flood protection infrastructure and elevation of storms. They looked 136 of the largest coastal cities in the world, and found that losses from flooding could hit $63 billion US a year by 2050.

The authors based their prediction on an increase in sea levels of between 0.2 and 0.4 metres by 2050 caused by melting continental ice sheets and warming seas.

The list of 20 cities most at risk of a 20 cm rise in sea level if no adaptation is undertaken, based on average annual losses due to floods, is topped by Guangzhou, Miami, New York, New Orleans, Mumbai, Nagoya, Tampa-St. Petersburg, Boston, Shenzen, Osaka-Kobe and Vancouver.

Without efforts to adapt, total annual losses could eventually top $1 trillion, the article said. By comparison, average global flood losses in 2005 were estimated to be approximately $6 billion US.

Flood defences in coastal cities have been designed for past conditions, and officials need to improve flood management and infrastructure, the study urged.

Those improvements will cost about $50 billion a year for the 136 cities the study considered.

Inaction is not an option, the team said.

However, the authors note that when defence measures are taken into account, Vancouver would fare significantly better than cities in developing countries with fewer resources to guard against flooding.

Still, Nicholls says strategies need to be monitored and adaptable.

"A key message of this is that flood risk is increasing all the time," said Nicholls.

Vancouver's adaption strategy

Last year, Vancouver became the first Canadian city to adopt a climate change adaptation strategy, which includes a coastal flood risk assessment and flood-proofing policies.

"I think it's another strong message about why that work is so urgent, but I don't think there's any stronger message than the floods that we saw in Calgary this past year, and in Toronto," said Coun. Andrea Reimer.

"You might be able to argue with a report. It's very hard to argue with the weather, and the observed impacts of extreme weather."

Climate change will bring heavier precipitation, higher daily temperatures, and more extreme weather events, she said.

The sea level in the city rose by almost 20 centimetres over the past century, and that rate is increasing rapidly, said Vancouver's report.

Vancouver's plan calls for the city to improve infrastructure to deal with flooding and extreme heat and storms.

Stephane Hallegatte, a senior economist with the World Bank and lead author of Nature paper, said policy makers should be considering early warning systems and evacuation planning.

"There is a limit to what can be achieved with hard protection: populations and assets will remain vulnerable to defence failure or to exceptional events that exceed the protection design," he said.