Climate change is increasing the amount of rain that hurricanes produce, and as warming picks up storms will become increasingly wetter and windier, according to new research. The findings are based on extensive modelling that involved millions of computing hours on a supercomputer, and they show that climate change is already affecting the intensity of storms.
"Climate change so far - from preindustrial to present - has contributed to increases in total storm rainfall from Hurricanes Katrina, Irma and Maria of about 5-10 percent," said the study's lead author Christina Patricola. "Our simulations also strongly indicate that we can expect to see even greater increases in rainfall and stronger winds by the end of the century," she told AFP. Patricola and co-author Michael Wehner, both researchers at the US Department of Energy's Lawrence Berkeley National Laboratory, started by analysing three major hurricanes: Katrina, Irma and Maria.
They used what Wehner refers to as a "hindcast attribution method" simulating first the scenario in which the storm occurred, and then a "counterfactual" storm in a world where climate change did not occur. By comparing the difference between the two models, the researchers were able to determine which elements resulted from climate change.
They found climate change at the time of Katrina, which devastated parts of the United States in 2005, had increased the storm's rainfall by 4-9 percent. It increased the rain from Irma, an immensely costly storm that hit in 2017, by six percent, and upped the rainfall from Maria, which devastated Puerto Rico the same year, by nine percent. The models suggested climate had not so far affected wind speed, but rainfall can be more devastating than high winds, causing deadly flooding and enormous damage.
Wetter, windier storms "We think that climate change has increased rainfall because the ocean and atmosphere have already started warming, which means the atmosphere can hold more moisture," said Patricola, while cautioning that other factors including changing storm dynamics could be at play.
The researchers then expanded their study and analysed a total of 15 tropical cyclones - storms that include Atlantic hurricanes, Pacific typhoons and cyclones around Australia. In addition to comparing the actual storms to pre-industrial conditions, they looked at how the storms would unfold under various theoretical climate change scenarios involving different temperature rises.
They found rainfall could increase between 15 and 35 percent in the future, with wind speeds increasing by as much as 25 knots. The study, published on Thursday in the journal Nature, comes after an active storm season that saw powerful hurricanes and devastating typhoons.
And it was published at the same time as another study in Nature that found urbanisation in the US city of Houston directly contributed to the rainfall and flooding in 2017's Hurricane Harvey. The research found urban growth ate up land that could have absorbed rainfall, but also led to Harvey producing more rain for reasons including the way buildings affect air flow.
Patricola and Wehner cautioned that their work uses one climate model, and further study will be needed to see if their results can be replicated. They also plan to study further the way climate change affects wind intensity and what other factors play a role in the impact of major storms. "More work is needed to interpret these changes to potentially improve resilience to extreme weather events," Patricola said.
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