A rash of flash floods has struck the US during this spring: Rhode Island, Tennessee, Arkansas, and most recently Oklahoma have all faced devastating floods that have resulted in the loss of property and in some cases tragic deaths. While flash floods have occurred throughout US history, the number of big floods this year appears abnormal at best, but not unexpected by researchers. Climatologists warned last year that an increase in floods and severe storms is very probable as the world warms.
A US report commissioned by the Bush Administration in 2007 and released in 2009 warned that the United States would see greater incidences of severe weather and heavier rainfall. The report, which looked at the US regionally, predicted that more precipitation in winter and spring in the Midwest would lead to increased flooding. In addition, the report predicted increases in flooding and severe weather for the Southeast.
The report stated that “the amount of rain falling in the heaviest downpours has increased approximately 20 percent on average in the past century, and this trend is very likely to continue, with the largest increases in the wettest places.”
At the time of the report’s release, Evan Mills, a Berkley scientist and contributor said: “This is the most thorough and up-to-date review ever assembled of climate-change impacts observed to date as well as those anticipated in the future across the United States.”
The science of climate change and increased flooding is straightforward: warmer temperatures cause increases water vapor in the air leading to heavier precipitation events. More water vapor also feeds severe storms, boosting their strength and severity.
Climate expert James Hansen told the Huffington Post that this would make abnormally large storms occur more frequently: “100-year floods will occur more often than one per century, 500-year storms will become more frequent, etc.”
The Tennessee flood—a true weather-aberration—was a one in a 1,000 year event; the Rhode Island floods and the flood this week in Oklahoma were a one in 100 year event; while the tragic flood in Arkansas last week was a one in a 10 year event. Despite this confluence of long-shot floods, last year also produced a string of record-breaking floods in North Dakota and Georgia.
The North Dakota floods prompted President Obama to speak in a rare moment about the impact of climate change on Americans.
“If you look at the flooding that’s going on right now in North Dakota and you say to yourself, ‘If you see an increase of 2 degrees, what does that do, in terms of the situation there?’ That indicates the degree to which we have to take this seriously,” the president stated in 2009.
In a recent interview with climate blogger Joe Romm, Dr. Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research, said that both the media and scientists were downplaying the well-established link between climate change and these floods.
“I find it systematically tends to get underplayed [by the media] and it often gets underplayed by my fellow scientists,” Trenberth says. “Because one of the opening statements, which I’m sure you’ve probably heard is ‘Well you can’t attribute a single event to climate change.’ But there is a systematic influence on all of these weather events now-a-days because of the fact that there is this extra water vapor lurking around in the atmosphere than there used to be say 30 years ago. It’s about a 4 percent extra amount, it invigorates the storms, it provides plenty of moisture for these storms and it’s unfortunate that the public is not associating these with the fact that this is one manifestation of climate change. And the prospects are that these kinds of things will only get bigger and worse in the future.”
For his part, Romm has recently suggested that the media—which has almost completely ignored the scientific connection between climate change and these floods—start referring to weather patterns clearly linked by data to climate change as ‘global-warming type events’.
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