|July 28, 2015|
Climate change 'triple threat' increases severe flooding risk in biggest cities
|America's biggest cities are at far greater risk of serious flooding in the coming decades than was previously thought, because of a "triple threat" produced under climate change, researchers said on Monday.|
A combination of sea-level rise, storm surge and heavy rainfall -- all functions of climate change -- exposes New York, Los Angeles, Houston, San Francisco, San Diego and Boston to a much greater degree, research published on Monday in the journal Nature Climate Change found.
"Call it a triple threat," said Steven Meyers, a scientist at the University of South Florida and one of the authors. "What this shows is that there is an increasing risk of compound flooding, from storm surge and rainfall at the same time."
About 40% of the US population lives in coastal cities -- where flooding in the wake of storms is already proving increasingly costly in built-up areas, swamping subway lines and electricity stations.
But the Nature study was among the first to explore the combined risks under climate change of sea-level rise, heavy rainfall and storm surges over broad stretches of the US coast.
In the case of New York City, the risks of flooding -- because of that combination of factors -- has doubled over the past 60 years, the researchers found. A 4ft storm surge, combined with 5in of rainfall, could be heading New York City's way once every 42 years, compared to about once in a century in the 1940s.
The increased risk was due to the combination of storm surge, rainfall and flooding.
"They are all somehow interconnected," said Thomas Wahl, the University of South Florida researcher who led the study. "If sea levels continued to rise, this would certainly have an effect on storm surges, and storm surges have an effect on compound flooding."
What that means is that it would not necessarily take a huge amount of rainfall to put New York or other cities underwater -- a storm surge could do that on its own, Wahl said.
However, the exact nature of the connections between sea-level rise, storm surge and heavy rainfall were still not fully understood, he said. It was too early to say whether the heightened risks were due entirely to climate change.
The researchers drew on weather records and tide gauges to estimate the risks of future flooding.
Many of the cities along the east coast were also at high risk of storm surges and heavy rain, while the west coast cities were expected to get off relatively lightly.
But the researchers said they were in the early days of establishing which cities were most at risk from the combination of sea-level rise and extreme weather.
The United Nations science panel has projected a global sea-level rise of about 4ft -- but many scientists believe that is an underestimate because it does not take into account the melting of ice sheets in western Antarctica.