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More Harveys

Thanks, climate change.

The extreme rains that inundated the Houston area during Hurricane Harvey were made more likely by climate change, a new study suggests, adding that such extreme flooding events will only become more frequent as the globe continues to warm.

“I guess what I was hoping to achieve was a little bit of a public service,” said MIT hurricane expert Kerry Emanuel, who published the study in the Proceedings of the National Academy of Sciences on Monday. “There are folks down in Texas who are having to rebuild infrastructure, and I think they need to have some idea of what kind of event they’re building for.”

In the wake of Harvey, many researchers pointed out that a warmer atmosphere holds more water vapor and that, as a result, a warmer planet should see more extreme rains. But Emanuel’s study goes beyond this general statement to support the idea that the specific risk of such an extreme rain event is already rising because of how humans have changed the planet.

Via climate modeling, Emanuel generated 3,700 computerized storms for each of three separate models that situated the storms in the climates of the years from 1980 to 2016. All of the storms were in the vicinity of Houston or other Texas areas. He examined how often, in his models, there would be about 20 inches of rain in one of these events.

Harvey produced closer to 33 inches over Houston. But in the tests under the 1980 to 2016 conditions, getting 20 inches of rain was rare in the extreme.

“By the standards of the average climate during 1981-2000, Harvey’s rainfall in Houston was ‘biblical’ in the sense that it likely occurred around once since the Old Testament was written,” wrote Emanuel, adding that in the much larger area of Texas, such rains did occur once every 100 years.

Then Emanuel performed a similar analysis, this time in the projected climates of the years 2080 to 2100, assuming the climate changes in some of the more severe ways scientists suggest it could.

The odds, accordingly, shifted toward a much greater likelihood of such events by 2100. Harvey’s rains in Houston became a once-in-100-years event (rather than a once-in-2,000-years event), and for Texas as a whole, the odds increased from once in 100 years to once every 5½.

This also meant, Emanuel calculated, that Harvey was probably more likely in 2017 than in the era from 1981 to 2000. In 2017, Harvey would be a once-in-325-years event. For Texas as a whole, in 2017 it would be a once-in-16-years event.

You can see the study here. This is the first study of its kind, so more research is needed to better understand what this means, but this is the world we live in. We can take steps to try to mitigate the damage, or we can live with the consequences. The MIT press release is here, and Ars Technica, the Atlantic, and the Associated Press have more.

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