Climate change made Harvey's 51 inches of rain 3 times more likely, scientists say

A burned out house is shown in an area flooded by Tropical Storm Harvey on Tuesday, Aug. 29, 2017, in Spring. A burned out house is shown in an area flooded by Tropical Storm Harvey on Tuesday, Aug. 29, 2017, in Spring. Photo: Brett Coomer, Houston Chronicle Photo: Brett Coomer, Houston Chronicle Image 1 of / 191 Caption Close Climate change made Harvey's 51 inches of rain 3 times more likely, scientists say 1 / 191 Back to Gallery

Global warming made Hurricane Harvey's 51 inches of rain three times more likely to occur when comparing today's climate to that of the 1880s, scientists say.

And if climate change continues unchecked, these extreme rain events will continue to occur, according to a paper presented Wednesday at the annual American Geophysical Union in New Orleans.

That's why policy makers "need to consider climate change in our design of infrastructure," said Antonia Sebastian, Rice University post doctoral researcher who is a coauthor on the paper.

The research presented Wednesday began soon after Harvey dumped feet of rain on the Houston area. World Weather Attribution -- an international effort to analyze the potential influence of climate change on extreme weather events -- decided to look at how greenhouse gases might have contributed to that extreme rainfall.

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Studies have consistently shown that greenhouse gas-induced warming should increase the amount of rain that falls during a tropical cyclone, according to the paper.

"In general, the maximum moisture content of air increases with 6% to 8.5% per degree warming," the paper states. "If relative humidity stays the same, which is the norm near oceans, the actual amount of water vapour in the air increases by the same amount."

To examine this idea, scientists used multiple climate models to analyze the amount of rain that fell over a three day period (Aug. 26-28) in Baytown, compared to other three-day rain events dating back to 1880.

For the purposes of the paper, they focused on extreme rainfall as the main cause of the flooding and did not take into account the impact of other factors such as Galveston Bay's sea level rise or the effect of Houston's urban development on flood plains.

Those models showed that global warming over the past century has increased the severity of three-day rain events on the Gulf Coast, according to the paper.

The intensity of rainfall increased 15 percent during that time, the paper states, while the likelihood that this much rain would fall was increased three fold.

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Scientists added that extreme rain events will only continue to happen as global warming gets more intense, which is why they say Houston needs to take this fact into account when making decisions about infrastructure.

They can do this, Sebastian said, by modeling for future climates and thinking about safety factors before construction, which can "have an impact on future resilience for the city of Houston."

Alex Stuckey is a science and environment reporter for the Houston Chronicle. You can reach her at alex.stuckey@chron.com or Twitter.com/alexdstuckey

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DEVELOPING STORM: Hurricane Harvey was the most destructive storm in Houston's history. The late-August storm dumped up to 60 inches of rain on southeast Texas, but the resulting damage was multiplied by actions taken ¬– and not taken – during the past 50 years. Our seven-part series explains why the storm's damage was both a natural and man-made disaster.

Part 1: Nature ruled, man reacted. Hurricane Harvey was Houston's reckoning

Part 2: Build, flood, rebuild: flood insurance's expensive cycle

Part 3: What's in Houston's worst flood zones? Development worth $13.5 billion

Click here to read all of our Harvey coverage.

GET ENGAGED:

— Where do we go from here? Seven Houston-area leaders discussed flooding causes and solutions at a Greater Houston After Harvey forum hosted by the Houston Chronicle in early December. Watch Wednesday night's keynote address by Jim Blackburn, co-director of Rice University's Severe Storm Prediction, Education and Evacuation from Disasters (SSPEED) Center. Read his thoughts on living around water.

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