“They’re so large and even though the core of the precipitation might be more concentrated in a smaller area, the broader impacts can be more expansive.”Īnd deadly floods from torrential rainfall devastated Eastern Kentucky and Missouri in late July last year, leaving $1.5 billion in damage in their wake. Hurricanes are producing more rainfall as they move inland after landfall and dissipate, for example.Ĭalifornia was hit with more than 10 so-called “atmospheric rivers” this past winter, bringing destruction as well as relief to the drought-stricken state.Īs the name suggests, atmospheric rivers are “a river in the sky,” said Northern Illinois University professor Allison Michaelis, an expert on the phenomenon. While major flooding is often considered a coastal phenomenon driven by hurricanes, intense rainfall also can produce disastrous inland flooding.
“The fact they’re not correcting for climate change means that their definition of a 100-year event is occurring much more frequently,” said Jeremy Porter, head of climate implications for First Street.Īlarmingly, in 20 of the most populous counties in the US, where a combined 1.3 million Americans live – largely in mid-Atlantic states including Pennsylvania, New Jersey and New York – these major events are forecast to happen around once every decade, First Street reported Monday.įirst Street found in much of the Northeast, the Ohio River Basin, Northwestern California, the Texas Gulf Coast and the Mountain West, the rainfall depths for a 1-in-100-year event could happen far more frequently, which First Street estimates could occur at least every 5 to 10 years. The problem: The federal rainfall analysis, which is managed by the National Oceanic and Atmospheric Administration, is updated infrequently and has not kept up with the climate crisis, which is intensifying precipitation events. It found half the American population lives in a county where a 1-in-100-year flood is at least twice as likely now as it had been in the past, coming once every 50 years, on average, rather than 100.
Intense rain events, like atmospheric rivers and torrential, training thunderstorms, are quickly making the idea of a “1-in-100-year flood event” obsolete, according to the report from First Street Foundation, a non-profit focused on weather risk research. A critical federal analysis of extreme rainfall is vastly underestimating the chances of flood events, with grave implications for everything from new roads and bridges to the rising cost of flood insurance, according to a new analysis.
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