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Homes are surrounded by water in the Azalea Lakes subdivision in Baton Rouge.

Climate change is significantly increasing the likelihood that intense, heavy rains of the type Louisiana saw in August will happen with greater frequency, researchers say in a report released Wednesday.

The torrential rain that caused widespread flooding in south Louisiana is, at minimum, 40 percent more likely to occur than it was in 1900 and will bring with it 10 percent more rainfall due to the effects of man-made climate change, according to researchers with the National Oceanic and Atmospheric Administration.

The new analysis of the heavy rain that hit Louisiana in August, done in cooperation with researchers at Princeton University, the Royal Netherlands Meteorological institute and the Red Cross Red Crescent Climate Center, found that it was significantly influenced by man-made climate change.

“What would have been a one in 100 storm (in 1900) would be a one in 70 year storm (now),” said Karin Van der Wiel, lead author of the paper and a research associate at NOAA’s Geophysical Fluid Dynamics Laboratory at Princeton University. “That’s quite an increase.”

The 40 percent greater chance of a similar storm occurring is at the lower range of what researchers found with the most likely scenario being that a similar storm is twice as likely to occur now than it was in pre-industrial 1900, she said.

“The unnamed storm  would eventually shower Louisiana with an estimated 7.1 trillion gallons of water – more rain than Hurricane Issac in 2012 and three times as much rain as Hurricane Katrina in 2005,” according to the researchers. This is just rainfall, explained Van der Wiel, and doesn’t reflect any flooding that might have occurred, pointing out that New Orleans flooding during Hurricane Katrina was storm surge, not rainfall.

The historic August flooding in south Louisiana led to the deaths of at least 13 people, damaged tens of thousands of homes and displaced tens of thousands of people.

“The Red Cross deemed the flooding in Louisiana the worst natural disaster in the United States since Superstorm Sandy slammed into the U.S. East Coast in 2012,” according to the report.

With such devastation, many people were asking what part, if any, climate change may have played in the weather event.

To find the answer, researchers used methods to help tease out climate influences from the normal variability of weather patterns.

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In simple terms for a very complicated process, the researchers took observed rainfall information over time and ran the information through two climate models.

“It tells you how extremes (of weather) have changed over time,” she said. “You can really pick things apart.”

The computer models help researchers look at changes and then allow them to look at potential causes for those changes to see what occurs when things like solar influence or greenhouse gases change.

“The central Gulf coast is a very complex region meteorologically,” said Gabriel Vecchi, with NOAA’s Geophysical Fluid Dynamics Laboratory.

However, the researchers were helped by practices already used at various rainfall events around the world, more advanced computer models and the partnerships researcher have developed to allow such analysis to be done,” Van der Wiel said.

The results match what the National Climate Assessment has been reporting with an expectation that more intense downpours in shorter periods of time would become more common leading to more flash flooding and damage.

The average amount of rain Louisiana gets each year has increased 20 to 30 percent in the last 100 years, according to the assessment.

According to the most recent NOAA report, Louisiana and other areas along the central Gulf Coast can expect more frequent occurrences of intense rain.

“The extreme rainfall in south Louisiana has longer-term implications for homeowners, local and federal governments, the humanitarian system and the insurance industry,” according to the report. “Knowing that this type of event is occurring more frequently today than in the past provides valuable insight into how governance and humanitarian institutions will need to evolve to be prepared in the future.”


Follow Amy Wold on Twitter, @awold10.