NASA Scientists Declare Drought of 1934 the Worst in 1,000 Years

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I guess it depends on what the definition of "worst" is. They used the criteria percentage of the US that had drought conditions, which was 72% in 1934. But you could also look at duration ( how many years ), or how dry it was (how low stream flow was based on tree ring studies). On the basis of those criteria, 1934 was the third or fourth worst drought in the past 1,000 years. Tree ring studies in California show a drought of 240 years duration that started in 850 AD, followed 50 years later by another drought of 180 years. I'd vote for that to be the worst drought.