A UCLA study released Tuesday predicts that massive, often-devastating storms — nicknamed “hundred-year storms” — may occur three times as often and be 20% more severe in the U.S. by 2079 due to climate change.
The UCLA researchers, in a paper published Tuesday 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 megastorms 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, who is also a fellow with the global conservation 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,” Swain 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 of damage and destruction caused by catastrophic flooding, 29.5% more than Tuesday.
When researchers combined projected climate change with projected population growth, they found the number of people at risk of the hundred-year floods could be about 50 million in the continental U.S.
The factors could create changes in areas that are currently sparsely populated and outside of flood zones, but with climate change and population growth, those areas will likely have higher population density and be likely to flood.
UCLA researchers used models to create plausible pasts and futures to increase the amount of available data by 40 times what was available from history alone. Previous projections of extreme precipitation relied on limited historical records, UCLA said.
“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, UCLA 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 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.