Natural causes, not human activity, behind last summer's drought

(CNN) -- Extreme natural events, not man-made climate change, led to last summer's historic drought in the Great Plains, a new federal study said Friday.

Drought occurred in six Plains states between last May and August because moist Gulf of Mexico air "failed to stream northward in late spring," and summer storms were few and stingy with rainfall, said a report by the National Oceanic and Atmospheric Administration.

"Neither ocean states nor human-induced climate change, factors that can provide long-lead predictability, appeared to play significant roles in causing severe rainfall deficits over the major corn producing regions of central Great Plains," the report summary said.

The drought in Wyoming, Colorado, Kansas, Nebraska, South Dakota and North Dakota was the worst since record keeping began in 1895, even eclipsing the notorious Dust Bowl droughts of 1934 and 1936, said study leader Martin Hoerling, a NOAA meteorologist.

"The event was rare, and we estimated maybe a once in a couple of hundred years event," Hoerling said. "But for as extreme as it was, it didn't have any strong indications for early warning.

"It's highly unlikely that this upcoming May to August will be as dry as last year's," he added, referring to the six states.