Study: Hurricanes are slowing down as climate warms, increasing flood threats

Hurricanes are slowing down worldwide, a new study reports. While this sounds like good news, it isn’t: It’s not that hurricanes’ wind speeds are diminishing, but instead how fast the entire storm moves, a new study reports.

As storms move slower, they can unload more heavy rain and pound coastal areas longer, increasing damage potential. 

"The slower a storm goes, the more rain it's going to dump in any particular area," said study author James Kossin, a climate scientist from NOAA. "Hurricane Harvey last year was a great example of what a slow storm can do."

Harvey stalled out over Texas last August, dropping Biblical rainfall that caused catastrophic flooding in the Houston area. As a result of Harvey, 89 people died and some 200,000 homes and businesses were destroyed, costing over $126 billion in economic losses.

More:‘Clear-sky’ flooding worsens across U.S. as sea levels rise, report says

Overall, the study looked at tropical cyclones, which is an umbrella term that includes tropical storms, hurricanes and typhoons. Kossin found that tropical cyclones' forward speed slowed by 10% between 1949 and 2016. 

For Atlantic hurricanes, the slowdown was 6%. But when Atlantic storms hit land — like Harvey did in 2017 — the study said the slowdown is a significant 20%.

This trend is "almost certainly increasing local rainfall totals and freshwater flooding,
which is associated with very high mortality risk,” Kossin said.

The cause? Most likely, changing wind patterns due to global warming. "The atmospheric circulation that drives tropical cyclone movement ... is expected to
weaken," NOAA said. 

Global warming is also projected to increase the severity of the strongest tropical cyclones.

Some outside scientists were skeptical of the new study. That's mostly because data before the 1970s is not reliable so it is hard to make such conclusions, according to University of Miami hurricane researcher Brian McNoldy.

Texas state climatologist John Nielsen-Gammon said "I just need more convincing that there actually has been a 10% motion change."

The study was published Wednesday in the peer-reviewed British journal Nature.

Contributing: The Associated Press