The drought of 2012 was more about unusual weather patterns than global warming, says a study. But its authors acknowledge the record-smashing event likely will be a puzzle for years to come.
Dry corn in Nebraska in a file photo from August 16, 2012. Federal scientists say that there is no clear explanation for 2012's droughts.
Nati Harnik/AP/File
EnlargeLast summer's record-smashing drought in the US heartland was driven far more by natural variability in weather patterns than by global warming, according to a new analysis by a team of federal and university researchers.
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The study represents what its authors call a first cut at untangling the factors contributing to the drought ? particularly to the hardest hit region in the Central Plains. The analysis does not explicitly exclude global warming as a player.
Instead, the researchers say that any one effect was too small to contribute to the time, place, and intensity of the drought in any significant way.
"The peculiar severity of summer 2012 can only be explained by an additional heavy role for random weather variability," the team concludes in a paper submitted to the Bulletin of the American Meteorological Society. The team's analysis also was released on Thursday as a 50-page report under the aegis of a federal drought task force led by the National Oceanic and Atmospheric Administration (NOAA).
The study touches on an event that has become a touchstone in the political debates over global warming's effect on the US.
It follows a report on weather extremes produced by the UN-sponsored Intergovernmental Panel on Climate Change. The report noted that on average, droughts in central North America "have become less frequent, less intense, or shorter." But the report also noted that over the course of this century, global warming's influence is likely to intensify droughts in the region.
At its height, the 2012 drought covered not only the six states where the dry-out was most intense ? Colorado, Wyoming, Kansas, Nebraska, Iowa, and Missouri. More than 75 percent of the continental US was bathed in yellow, orange, and russets on drought maps denoting conditions ranging from abnormally dry to exceptional drought.
Crops shriveled; the corn yield was 26 percent below initial US Department of Agriculture projections ? representing a loss equivalent to the entire harvest in 1961, the research team calculates. Low water curtailed barge traffic on the Mississippi River. The economic losses are still being tallied, although by July 2012, the event had cost the US economy $12 billion.
In the six-state region the team analyzed, the May through August period was the driest in 117 years. Overall, the team put the recurrence rate for a drought of that severity at once every few hundred years.
The country, meanwhile, is heading into another warm season with a higher percentage of the continental US experiencing dry conditions than it did last year. Federal drought statistics released April 9 show that in each of four out of five severity categories, abnormal dryness or drought covers about 12 percent more of the continental US today than it did this time last year. The fifth category, exceptional drought, covers only 2 percent of the nation, but that's double the level for this time last year.
The current drought forecast, which covers April 4 to June 30, shows drought conditions easing from portions of northeast Texas through western Wisconsin and Minnesota. Forecasters expect modest improvement into the central and northern Plains. But from central and western Texas north through the Rocky Mountain states to California and eastern Oregon, drought is expected to continue or expand its reach.
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