Hurricanes are slowing down, causing more damage in coastal communities

Mindy Sparks
June 8, 2018

"Long-duration or slower-moving storms, even when weaker, can have exacerbated impacts through prolonged wind exposure [in addition to] flooding", according to Colin Zarzycki, a project scientist with the National Center for Atmospheric Research who was not involved with the study.

Their forward speed has decreased globally by about 10 percent since 1949, the study said, making these storms more likely to drop heavier rain as they spend longer amounts of time over the affected areas, increasing the risk of flooding.

Kossin's work was based on details of nearly 70 years' worth of storms, but he made no attempt to determine what was causing the slowdown.

Worldwide cyclones have become sluggish, slowing down 10 per cent over the past 70 years.

But Kossin chose to investigate it, based on the expectation that climate change is already altering the general, large-scale circulation of the atmosphere, within which hurricanes are embedded and by which they are steered.

"The slower the storm gets, the more rain an area will get", said Jim Kossin.

And at the same time, a hotter atmosphere can hold more moisture.


But Kossin can't say whether Harvey's rains are a model for the future.

Although this study did not investigate directly what is causing the tropical cyclones to slow, it presents a hypothesis that was the basis for the research. "And that has effects on circulation - typically slows it down".

"Roughly 7 percent more water vapor per degree C of warming", Kossin said.

But Kossin, in his paper, writes that he wouldn't expect big changes in his results due to different means of measurement, since "estimates of tropical-cyclone position should be comparatively insensitive to such changes".

The reduced speed leads to heavier rainfall and an increased risk of flooding.

Dr Christina Patricola, from the Climate and Ecosystems Sciences Division at University California, Davis, says the findings raise several questions, especially regarding "stalled" tropical cyclones. "We'll need more formal attribution studies to disentangle these factors".

Other reports by Iphone Fresh

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