Climate change has intensified hurricane rainfall, and now we know how much

Climate change has intensified hurricane rainfall, and now we know how much

How humans are transforming the hurricanes of the future

Share Share How humans are transforming the hurricanes of the future share tweet Linkedin Reddit Pocket Flipboard Email Hurricane Harvey from the International Space Station, August 28th, 2017. Photo by Randy Bresnik/NASA Climate change is already making devastating hurricanes wetter — and similar storms are likely to unleash more rain and faster winds by the end of the century, new research says.

When Hurricanes Harvey, Irma, and Maria struck the US in rapid succession in the fall of 2017, the storms and their aftermaths killed thousands of people and caused an estimated $265 billion in damage. Harvey became the second costliest storm after Hurricane Katrina, which devastated New Orleans in 2005. Now, new research published today in the journal Nature suggests that climate change made Irma, Maria, and Katrina drop more rain than they would have in a pre-industrial world. The study also predicts that in a warmer future, these storms would be even wetter and windier. A second paper (also published today in Nature) took a closer look at Hurricane Harvey. It shows another way people may have made the storms rain and flooding more severe: by building cities.

Hurricanes should, theoretically, be more intense and wetter on a hotter planet. After all, warm ocean water fuels hurricanes, and warmer air holds more moisture — which means more rain. Recent studies back that up; analyses of Hurricane Harvey, for instance, reported that 15 percent or more of the rainfall could be attributed to global warming.

Todays paper provides yet more evidence about the ways in which climate change shapes extreme weather events, says Dim Coumou, an atmospheric scientist at the Potsdam Institute for Climate Impact Research who was not involved in the study. Its a very important confirmation of our understanding of how hurricanes change with global warming. Climate scientist Michael Mann says that some of the results make perfect sense. We expect greater rainfall and flooding from hurricanes as ocean surface temperatures and atmospheric moisture content increases in a warming world. But he cautions that the papers use a single climate model, so it is difficult to draw other general conclusions from these studies.

The study started because Christina Patricola, a climate scientist at Lawrence Berkeley National Laboratory, wanted to find out how exactly climate change fit into the recent spate of devastating storms. So she simulated more than a dozen hurricanes, including Hurricane Katrina. She and her co-author Michael Wehner plugged in ocean temperature, atmospheric conditions, and watched the simulated storms spin toward land.

WASHINGTON — Humans helped make recent devastating U.S. hurricanes wetter but in different ways, two new studies find.

Hurricane Harvey snagged on the skyscrapers of Houston, causing it to slow and dump more rain than it normally would, one study found. The citys massive amounts of paving had an even bigger impact by reducing drainage. Land development in the metro area, on average, increased the chances of extreme flooding by 21 times, study authors said.

A second study looked at last years major Hurricanes Maria and Irma and 2005s deadly Katrina and used computer simulations to see what would have happened if there had been no human-caused global warming. The study found that climate change significantly increased rainfall from those three storms, but did not boost their wind speed.

Houston was a literal drag on Harvey as it sloshed through, with the storm getting tripped up by the skyscrapers, said study co-author Gabriele Villarini, a civil and environmental engineering professor at the University of Iowa.

Co-author Gabe Vecchi, a climate scientist at Princeton University, said that forced the storm to move up higher, causing more concentrated rain over Houston and slowing, which also made more rain.

This effect is dwarfed, though, by the paving and building that dont allow water to sink into the ground, Vecchi said.

Harveys record rainfall reached 5 feet in one spot near Houston. The scientists used computer simulations to see the effects of urbanization. In parts of the Houston metro area, the effects of development ranged from a 10 percent higher risk of extreme flooding in the less developed northwest to nearly 92 times the risk in the northeast, they reported.

Thats on top of the unique weather patterns that made Harvey slow down and stall and climate change which brought more water into the storm, Vecchi said.

MIT hurricane and climate expert Kerry Emanuel, who wasnt part of the study, called the Harvey study “a real advance in our understanding of hurricane impacts on urban areas.”

But Texas state climatologist John Nielsen-Gammon wasnt convinced. He said the team used generic shapes instead of the actual Houston skyline. He said the storms wind speeds may have slowed, but thats different from the storms forward movement slowing.

The other study in Nature looked at a variety of historical damaging storms and tried to calculate past and future effects of climate change. In three cases, the scientists simulated the storms without the changes in the climate from greenhouse gases, showing that global warming increased rainfall 8.9 percent in Hurricane Maria , 6.3 percent in Hurricane Irma and 8.7 percent in Hurricane Katrina .

Maria hit Puerto and Rico and other parts of the Caribbean. Irma hit the Caribbean and Florida, while Katrina struck New Orleans and the Gulf Coast.

In Marias case, a warming climate concentrated heavier rain in the center of the storm and reduced it on the edges, said co-author Michael Wehner, a climate scientist at the Lawrence Berkeley National Laboratory.

For 15 storms, which included the devastating Typhoon Haiyan , the potent Gilbert and 1992s Hurricane Andrew , the scientists projected future warming and found future versions of the same storms would be significantly wetter and stronger.

“We are beginning to see a climate change influence emerge on tropical cyclones and thats coming out as rainfall,” said study lead author Christina Patricola, an atmospheric scientist at the national lab.

Although replicating a storm in a different climate is difficult and cant account for certain changes, this work bolsters science understanding of how climate change alters hurricanes, Emanuel said.


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