A satellite image of 2017’s Hurricane Harvey as it approached Texas. Photo credit: European Space Agency, via Wikimedia Commons

A study last week predicts that massive, often-devastating “hundred-year storms” may occur three times as often and be 20% more severe in the U.S. due to climate change.

The researchers, in a paper published in the American Geophysical Union journal Earth’s Future, found that if greenhouse gas emissions continue to increase at a rapid rate, the continental U.S. would likely see such mega-storms every 33 years.

The occurrence of historic rainfall events, like the ones that caused Hurricane Harvey in 2017 and California’s Great Flood of 1862, are likely to increase faster than lower-magnitude events, which already happen about every decade, according to UCLA climate scientist Daniel Swain.

Swain also serves as a fellow with the global organization The Nature Conservancy.

“The five-year flood, the 10-year flood – those aren’t the ones that cause huge amounts of damage and societal disruption,” he said. “That comes when you get 50- or 100-year floods, the low-probability, but high-consequence kinds of events.”

The researchers found that some areas, particularly the West Coast and the hurricane-prone Southeast, will likely see larger relative increases than other areas of the U.S.

The team’s combination of climate, water physics and population models predict that if extreme precipitation alone increases, an additional 12 million people would be at risk from destruction caused by catastrophic flooding.

When researchers combined projections on climate change with those for population growth, they found the number of people at risk of hundred-year floods could be about 50 million in the continental U.S.

The factors even could create changes in areas that are currently sparsely populated and outside of flood zones. With climate change and population growth, those areas will likely have higher population density and leaving them vulnerable to flooding.

UCLA researchers used models not just for predictions, but also to glean information from the past. That increased the amount of data by 40 times what was available the historical record alone, which is limited, according to UCLA.

“We don’t just have one 100-year event we can pull from the historical record. We have lots of really severe, rare events we can pull out to give us a better sense of how they’re likely to change,” said Swain.

People in the continental U.S. should expect a significant increase in flooding over the next 30 years, even if global warming is moderate.

A temperature increase of about 2.7 to 4.5 degrees Fahrenheit globally would expose over 30 million additional people to a 100-year flood within the next 30 years, the researchers projected.

Global temperatures have already increased over two degrees Fahrenheit, and UCLA researchers say the term “100-year flood’ is “fast becoming outdated.”

The changes in precipitation that the researchers predict have already begun, according to James Done, co-author of the paper and a climate scientist at the National Center for Atmospheric Research.

He said the nation’s infrastructure – including flood control channels – is not designed for the scenarios researchers say are likely to occur.

– City News Service

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