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Climate change probably played a major role in Louisiana floods: NOAA

Human-caused climate warming increased the chances of the torrential rains that unleashed devastating floods in south Louisiana in mid-August by at least 40 percent, according to a team of NOAA and partner scientists with World Weather Attribution (WWA) who conducted a rapid assessment of the role of climate on the historic heavy rain event.

“We found human-caused, heat-trapping greenhouse gases can play a measurable role in events such as the August rains that resulted in such devastating floods, affecting so many people,” said Karin van der Wiel, a research associate at NOAA’s Geophysical Fluid Dynamics Laboratory and the lead author. “While we concluded that 40 percent is the minimum increase in the chances of such rains, we found that the mostly likely impact of climate change is a near doubling of the odds of such a storm.”

Extreme rain risk rising

Models indicate that the return period for extreme rain events of the magnitude of the mid-August downpour in Louisiana has decreased from an average of 50 years to 30 years. A typical 30-year event in 1900 would have had 10 percent less rain than a similar event today, for example, 23 inches instead of 25.

For the assessment, scientists conducted a statistical analysis of rainfall observations and used two of NOAA’s high-resolution climate models to understand how the odds have changed for such three-day events between the early 20th century and the early 21st century. The results were consistent using observational data and climate models.

The research focused on the central US Gulf Coast, and investigated events as strong as that observed at the height of the storm (August 12-14) to provide a regional context and a broader assessment of risk. The climate model experiments involved altering the climate based on levels of greenhouse gases in the atmosphere, aerosols such as soot and dust, ozone and natural changes in the sun’s radiation and from volcanic eruptions for various periods of time to assess how extreme rainfall events respond to climate changes.

www.noaa.gov



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