Climate change, cities magnify torrential storms, studies say

By on December 6, 2018

Flooding from Hurricane Matthew. (Voice)

Lori Wynn
Coastal Review Online

If it seems like hurricanes in recent years are dumping more rain and causing more flooding when they make landfall, it’s because they are.

According to two papers recently published in the science journal Nature, the deluges are the result of climate change and human activity.

In some cases, cities themselves may be contributing to extreme rainfall.

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The first paper simulated how 15 historically destructive hurricanes across the globe would have developed in different scenarios: pre-industrial, modern and three potential late-21st century climates.

It found that climate change increased the rainfall from hurricanes Katrina, Irma and Maria by 4 to 9 percent and could cause up to 30 percent more storm-derived rain in the future.

This comes as many parts of Eastern North Carolina are still recovering from Hurricane Florence, a storm that dumped a reported 9 trillion gallons of rain across the state and raised the bar for flooding in North Carolina.

While Florence arrived too late to be included in this research, it’s conceivable to draw lines between the two.

Charles Konrad, director of the Southeast Regional Climate Center and a professor in the geography department at the University of North Carolina Chapel Hill, agreed. He explained that Florence’s size and slow forward momentum were big factors in the amount of rain that fell.

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“There needs to be proper research done, but there’s the suggestion that the sea surface temperatures are warmer in that part of the Atlantic (where Florence traveled), and so we can certainly hypothesize that the rainfall rates were a bit greater with Florence — at least slightly greater — because with the ocean being warmer, there’s more evaporation and water vapor going up into the atmosphere,” Konrad said.

“That’s something, if properly done, a climate attribution study might effectively show.”

The second paper used data from Houston during Hurricane Harvey in 2017 and compared it to models of that area if the city had never been built. The conclusion was that “urbanization exacerbated not only the flood response, but also the storm total rainfall” and the probability of extreme flooding events was increased around 21 times, according to the paper.

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Konrad explained that the tall buildings in Houston create a “surface roughness” that ends up putting more moisture into the air of a storm making landfall.

“When the winds carrying all this moisture hit these buildings, all of them together, you get more lifting and then that squeezes more rain out of the atmosphere,” he said. “It makes perfect sense.”

Sankar Arumugam, a professor and university faculty scholar at N.C. State’s Department of Civil, Construction and Environmental Engineering, has researched similar trends for the Southeast.

He said that while a slow-moving hurricane will almost always come with drenching rains, combining that with an urban setting that tends to trap air and moisture can help increase precipitation.

“We clearly see a trend in the tropical storm contribution in the precipitation,” he said.

To see if some of that moisture is going back into the air, rather than into nearby streams or creeks and rivers, or streamflow, he compared the records of rainfall amounts with that of streamflow measurements.

“What we find is that they do exhibit the trend in terms of increasing amounts of tropical storm contribution … but we don’t see a similar trend on the streamflow,” Arumugam said.

“The point is that perhaps – and this is not a conclusion – but perhaps the rural watersheds dampen that (rain) signal better as opposed to urban watersheds.”

Konrad said that as hurricanes or tropical storms make landfall, there’s always some additional “uplift” as onshore winds hit the land surface and any trees or buildings that may be on it.

“So it’s really a scale thing, right? Houston is a very large city and there’s been a tremendous amount of development and there are quite a few tall buildings,” Konrad said.

“But it’s intriguing to think that, yeah, with a lot of tall buildings – take Myrtle Beach, for example, where there’s just miles and miles of tall buildings – perhaps is increasing the rates of rainfall there locally when tropical systems are making landfall.”

These papers could not show a link between climate change and its effect on the intensity of hurricanes, but the scientific community has agreed for decades that the trending impact of human activity on the climate will result in more frequent extreme weather events.

“We know meteorologically that as the world warms, there’s greater potential for higher rainfall rates,” Konrad said. “There’s also been work, too, that shows a really marked slowing down of hurricanes – not every single hurricane … but you’re getting more situations where they move really slow or stall out like we saw with Hurricane Florence. That’s something that connects with climate change.”

More severe extreme weather events are something we need to get used to, he said.

“We need to really understand that this is basically a new normal that’s developing here,” Konrad said.

“We’re seeing extreme precipitation and flooding occurring at a higher frequency than we’ve seen in the past inland … We need to really rethink what the 100-year flood is. We need to think about these events that, in the past, we would consider to happen once every thousand years — these are occurring more frequently. And we need to really think hard about how to get more people out of harm’s way.”

Comments

  • Michael

    Florence was a slow mover bc of steering currents. Actually weakened a lot before landfall. Before 2017 it was over a decade since the USA even experienced a major hurricane. We need to stop erasing the past to prove theories. Look at the 1930s weather. Hurricanes in the 50s ect. We can’t ignore the past. We definitely need to help ones in harms way. Just don’t erase history to prove and unproven fact. The Atlantic this year stretching to Africa during the summer was wayyyyy below average.

    Thursday, Dec 6 @ 1:27 pm
  • J

    Michael, climate change and urbanization in America are proven facts. We are being shortsighted if we ignore science and human impact on our planet in an effort to bolster the economic well-being of a few special interest groups, such as the fossil fuel industry. Both papers described in this article focus on historical comparisons. “The first paper simulated how 15 historically destructive hurricanes across the globe would have developed in different scenarios: pre-industrial, modern and three potential late-21st century climates.” “The second paper used data from Houston during Hurricane Harvey in 2017 and compared it to models of that area if the city had never been built.” You are correct that “we can’t ignore the past”. The historical view of these studies confirms what has been reported by scientists all over the world: the impacts of severe weather events like hurricanes are worsening due to climate change and urban development.

    Friday, Dec 7 @ 5:39 pm
  • Really

    Then why would you be part of the problem @J? Fact: Filling up your vehicle this week you helped “bolster the economic well-being of a few special interest groups, such as the fossil fuel industry” The house you’re living in is part of the urbanization creating the intensified storms. I suggest from now on you walk everywhere you go and you must live in a grass hut constructed of dead marsh grass. Come on @J, walk the walk , do your part, be part of the solution not the problem! Lol!

    Saturday, Dec 8 @ 10:00 am
  • Runnerguy

    Climate change is real life here on the Outer Banks.

    Sunday, Dec 9 @ 3:06 pm
  • dave

    Hey Michael. Just like all the science that goes into making cars, Mars rovers, putting man on the moon, I phones, etc is phony too. Yeah, 98.7% of all the worlds top climatologists have it wrong huh?

    Monday, Dec 10 @ 8:42 am
  • dave

    Really….you really (no pun intended) have a hard time seeing the big picture don’t you? And whats with your obsession on filling up cars with gas? I “really” wonder if you have the intellectual resources and/or the educational background to actually grasp this.

    Monday, Dec 10 @ 10:20 am

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