ARI SHAPIRO, HOST:
We're almost a week into hurricane season, and places like Houston, Texas, still have not recovered from last year's storms. Scientists say part of the reason last year's season was so devastating is that the hurricanes themselves are changing. NPR's Rebecca Hersher reports.
REBECCA HERSHER, BYLINE: Hurricane Harvey hit the Texas coast on August 25, 2017, and then, for nearly a week, it made its way real leisurely across the southeastern part of the state.
(SOUNDBITE OF NEWS MONTAGE)
SHAPIRO: The situation in Houston is getting more dire by the hour...
RACHEL MARTIN: Hurricane Harvey has brought unprecedented levels of flooding...
DAVID GREENE: Twenty inches of rain in some areas so far...
WADE GOODWYN: A trillion gallons, like three feet of rain. This is one of the greatest weather catastrophes in the nation's history.
HERSHER: In Houston, it was a new kind of hurricane disaster - a massive urban inland flood. James Kossin studies global hurricanes at the National Oceanic and Atmospheric Administration.
JAMES KOSSIN: Hurricane Harvey obviously was a real outlier in terms of the amount of rain it dropped. And the amount of rain it dropped was due almost entirely to the fact that it moved so slowly.
HERSHER: And Kossin says that's getting more common for tropical cyclones around the world.
KOSSIN: They seem to have slowed down just about everywhere.
HERSHER: The reason - climate change. As the poles get warmer, the big currents of wind between the poles and the tropics slow down. Storms ride on that wind, kind of like a boat in a stream.
KOSSIN: Yeah, the wind itself that carries the tropical cyclones within it is slowing down and therefore the tropical cyclones are slowing down.
HERSHER: In a study published today in the journal Nature, Kossin found storms all over the world have slowed down 10 percent in the last 70 years. Hurricanes moving over land in North America specifically have slowed down even more than that on average. Kossin says that's all really bad news.
KOSSIN: If you think of it, all of the things that come along with a tropical cyclone visiting your neighborhood - they're all bad. And you don't want them to last very long. If the wind's blowing really hard and it blows a few more hours than it would have, the likelihood of knocking that structure down increase, so you get more rainfall, you get more wind damage, you also get greater storm surge. Slower storms will have a tendency to push a larger wall of water in front of them. So it's kind of a triple threat.
HERSHER: He also says these storms could be more deadly because we're not used to having storms hang out over inland cities.
KOSSIN: People don't necessarily evacuate from inland locations, and so they get a lot of freshwater flooding. And then you also get these compound events of mudslides, and that's really where we get a really large loss of life.
HERSHER: He warns a lot of places need to reassess their hurricane risks. That will probably mean new evacuation plans, flood maps and emergency systems for a lot of cities. Rebecca Hersher, NPR News.
NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.