Widely used index may have overestimated drought

[OKIsItJustMe]

http://www.earthmagazine.org/article/widely-used-index-may-have-overestimated-drought

[font face=Serif][font size=5]Widely used index may have overestimated drought[/font]

[font size=3]The severity and frequency of drought are expected to increase worldwide as climate change leads to a warmer atmosphere and regional changes in precipitation, and some research has shown that drought is already increasing. But a new study concludes that the increase in drought claimed by previous studies has been overestimated and that there has actually been little increase over the last 60 years.

A team of researchers from Princeton University and Australian National University suggests that a widely used tool for assessing drought — the Palmer Drought Severity Index (PDSI) — isn’t up to the task of large-scale drought assessment.

The PDSI was developed in the 1960s by Wayne Palmer, a meteorologist for the U.S. Weather Bureau, as a way to convert multiyear temperature and precipitation data into a single number representing relative wetness for each region of the United States. Zero, for example, represents average wetness whereas negative 3.4 would indicate severe drought and positive 2.8 would mean an area was moderately moist.

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Aiguo Dai, a climate scientist at the University of Albany, State University of New York, says he is skeptical about the new conclusions. “I think it’s premature to conclude that the drying trend is [less than what has been reported over] the last 50, 60 years,” Dai says. In particular, Dai takes issue with the precipitation data Sheffield’s team used, as well as the time period used to calibrate the model. “Essentially, they enlarged the standard deviation of the PDSI,” he says.

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