The current drought in the U.S. certainly feels like it's one for the history books. But it's likely not the worst North America has seen in the last millennium. A new study from NASA shows that a drought in 1934 was by far the worst to strike the continent in 1000 years.

Scientists from NASA and the Lamont-Doherty Earth Observatory have been looking at tree-ring data from 1000 to 2005, as well as contemporary weather records, to examine several exceptional drought events. They've determined that the drought of 1934 was off-the-charts bad, with extremely dry conditions spreading over 71.6 percent of North America. The second-worst drought was back in 1580. (There aren't final figures for 2014 yet.)

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"It was the worst by a large margin, falling pretty far outside the normal range of variability that we see in the record," said NASA's Ben Cook of the 1934 event.

The 1934 drought, showing how dry conditions covered almost 3/4 of the continent.

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The 1934 drought was actually one of four drought events that happened one after another over an entire decade, without normal weather patterns in between for the country to recover. The droughts of 1930-31, 1934, 1936, and 1939-40 would collectively be named the Dust Bowl for the way they transformed large swaths of the Midwest and Western U.S. into swirling black walls of dirt.

The most frightening thing about the 1934 drought was that it was exacerbated by human intervention. Although a high-pressure weather system over the Western U.S. suppressed normal rainfall patterns (similar to what happened last winter, and what might happen this winter again), it was the poor land management practices by farmers which ended up causing the deadly dust storms that spring.

A dust storm in South Dakota. Photo via National Archives FDR Library Public Domain Photographs.

The dust storms acted as a kind of solar shield, preventing natural sunlight from reaching crops, but they also blocked the evaporation process that would normally generate rain clouds. As spring turned into summer, it was dust storms, not rain storms, which were pushed eastward by that high-pressure system. This cycle repeated across the U.S. for several years, until finally, above-average rainfall ended the decade of dryness.

The good news is that more efficient farming techniques pretty much guarantee that we won't see Dust Bowl-level storms in the U.S. again. However, due to other variables in weather events which are brought on by climate change, we may find ourselves just as vulnerable to a megadrought that lasts a decade—or longer. [NASA]

Top photo: Cimarron County, Oklahoma, by Arthur Rothstein, Farm Security Administration


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