STEVE INSKEEP, HOST:
Now let's get some symptoms of the health of the planet. The floods that hit Louisiana last month were caused by rainfall unlike anything seen there in centuries. A half a year's worth of rain fell in southern Louisiana in a few days, and a lot of the flooding was in unexpected places. As NPR's Christopher Joyce reports, scientists suspect a changing climate could make that more common.
CHRISTOPHER JOYCE, BYLINE: When nature throws a haymaker, you can depend on the Weather Channel to provide a vivid analysis.
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UNIDENTIFIED REPORTER: Wrap your head around this 30-inch rainfall totals, 30-inch rainfall totals. Louisiana hasn't gotten punched in the gut.
JOYCE: Thirty inches in just three days, the kind of cataclysm that some might call an act of God.
NICHOLAS PINTER: Our experience is that these kind of - call them acts-of-God explanations are served up just a little too easily.
JOYCE: Nicholas Pinter is a geologist at the University of California, Davis and a flood expert. He says while there have always been super downpours, they're not so rare anymore.
PINTER: Hundred-year floods, other large events are occurring bigger and more frequently than the published probabilities predict.
JOYCE: And they're inundating places that usually haven't flooded. In Louisiana, for example, satellite photos show that about a third of the flooding was outside the flood plain. The flood plain is the area that historically gets inundated by big floods, once-in-a-century floods. Pinter says he needs more hard evidence to prove it, but it appears that these kinds of floods are on the rise.
PINTER: Maybe we're seeing a different character of flood event beginning to appear, more like a climate-driven flash flood event affecting these big river systems which might be a new and different phenomenon that we need to throw into the statistics, maybe.
JOYCE: A heavy rain, for example, that flashes down onto urban areas and just overwhelms sewers and drains. Paul Osman agrees. Osman is the floodplain manager for the state of Illinois. He calls these sudden deluges drainage events. They aren't necessarily caused by rivers rising over their banks.
PAUL OSMAN: We found that 90 percent of our damages in Illinois are not traditional overland flow damages, but rather heavy rainfall events that cause basements to backfill with water.
JOYCE: Osman says between 2007 and 2014, almost all the flood damage in urban Illinois occurred outside of traditional floodplains.
OSMAN: There's no doubt all the scientific evidence points at those rainfalls - are changing. We're having a lot more of these kind of intense short-duration storms that happen in relatively small geographic areas like Louisiana.
JOYCE: That's consistent with what climate scientists have been predicting. A warmer atmosphere holds more water vapor and can create bigger, more intense storms. And the federal government's latest Climate Assessment notes that extreme downpours are rising in parts of the U.S. Osman says many drainage systems just can't handle these intense storms.
OSMAN: Most of those storm sewer designs were built on, you know, historic records and historic rainfall events that are no longer the case.
JOYCE: If historic rainfall data no longer hold true, that's a problem for the Federal Emergency Management Agency. FEMA draws up maps that show where floodplains are. People with federally-backed mortgages in the highest-risk areas have to get flood insurance. People outside those areas don't. Kathleen Schaefer spent 10 years drawing flood maps at FEMA. She says FEMA only looked back at historical rainfall data, not forward at what a changing climate may bring.
KATHLEEN SCHAEFER: You had to ignore climate change. All of the mapping had to be based on the existing conditions.
JOYCE: Schaefer says local flood managers have begun to suspect that existing conditions have changed and that FEMA's flood maps may be out of date. But if they come to Washington, D.C., looking for help, they have to mince their words.
SCHAEFER: They can't even use the word climate change. They call it a slow-moving disaster which is sort of a code word for climate change.
JOYCE: Recently, though, FEMA has begun to consider climate change in its flood analyses. But the agency only updates its flood insurance maps every five years, and the weather may be changing faster than that. Christopher Joyce, NPR News.
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