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Calamitous flooding likely to continue


The number of catastrophic floods of the kind that have historically occurred every 50 to 200 years is likely to increase as a result of climate change, according to a UCLA-led study released this week.

Scientists project that the number of severe floods, the sort that happen every 10 or 20 years, won’t change much for the remainder of the century—the incidence could even decrease in some places—but the number of the most catastrophic floods will likely increase.

Daniel Swain, a UCLA climate scientist and co-author of the study, said the reason for the discrepancy is a logical one: Warming due to climate change can also cause land to dry out—the current drought conditions across western North America are an example—and drier land can absorb more water. But the new research reveals that the phenomenon only goes so far.

“If you have drier watersheds, they have more capacity to absorb the increasing extreme rain,’’ Swain said. “But above a certain threshold, when you get to the most extreme events, that logic may no longer hold. At a certain point, the precipitation is going to saturate the soil anyway—even the driest soil—and completely overwhelm the watershed.’’

The research by scientists at UCLA, the University of Freiburg in Germany and other institutions was published in the journal Communications Earth & Environment.

Because catastrophic floods occur so infrequently, there aren’t many recent examples to observe, and many climate records date back 50 years or less. However, previous research led by UCLA projected that such floods are likely to increase in both frequency and magnitude due to climate change.

In California, for example, the likelihood of what used to be considered a once-in-a-lifetime event, one that could cause up to $1 trillion in damage and force the evacuation of millions of people, has increased by 300 percent to 400 percent.