EVANSVILLE – If a “once in every 100 years" rainstorm hits Vanderburgh County, it could be heavier than in decades past. And it could happen a lot more frequently than once every 100 years.
That's part of the findings of a massive study from First Street Foundation: a nonprofit that delved into National Oceanic and Atmospheric Administration data and found that crippling rainfall is becoming more common – and more powerful – across large swaths of the U.S.
In fact, the study says two of the top-five hardest-hit areas in the country could be a pair of Southern Indiana counties: Floyd, which “led” the study in how often it could absorb historic storms, and Clark, which ranked fourth.
According to the study, which the Washington Post parsed into a searchable data table, Floyd County could get a 100-year storm – or an event that has a 1 percent chance of happening each year – about once every 7 years.
Almost five inches of rain could fall there in an hour – about two inches more than NOAA’s estimate. Clark, meanwhile, would get such a storm around once every eight years.
The study used a peer-reviewed model to analyze NOAA’s Atlas 14: a “precipitation frequency data server” that estimates how much rain would fall in certain areas, in certain increments of time, in the event of heavy storms.
First Street found that in some parts of the country, climate change has rendered the NOAA’s figures woefully inadequate. A warming planet could supercharge already heavy storms, leaving behind devastating floods.
That was certainly the case in Switzerland County, Indiana last year.
The Post opened its story with Kim Schultz, who watched a creek near her home outside Madison swell into frothing rapids that swept away cattle and cars, damaged roads and bridges, and killed a 61-year-old woman after the water ripped her house from its foundation.
The story also singles out the horrific flooding that raged across Eastern Kentucky last July.
“I’ve never seen anything like it,” Schultz told the Post. “You just don’t realize the power of water until you see it for yourself.”
How could rainfall in Vanderburgh County change?
The 25-page study says that NOAA has especially underestimated the likelihood of historic rains in five disparate parts of the country.
“In much of the Northeast, the Ohio River Basin, Northwestern California, the Texas Gulf Coast, and the Mountain West, the depths corresponding to a 1-in-100 year event … are actually modeled to occur at least every 5 to 10 years,” it reads.
Vanderburgh County doesn’t fall within that range, but it’s not far off. According to the Post’s table, we could see a 100-year event about every 21 years. It could happen in Warrick County every 19 years, Posey every 25, and Henderson County, Kentucky about every 31.
Other parts of the country, though, could see fewer heavy rain storms than NOAA data suggest. Riverside County, California, for instance, is slated to get a 100-year storm every 357 years, the study found.
“Infrastructure (in such areas) is therefore being built to a level far above what would be sufficient to protect from the area’s actual precipitation risk, using extra resources that could be better spent elsewhere,” it reads.