A new paper in Nature says that it seems that, globally, drought has not increased much, contrary to previous studies saying it has. The problem is to do with how you assess drought. The matter appears to remain controversial:
Sheffield and colleagues calculated global drought trends from 1950 to 2008 using both equations on multiple datasets. Notably, they found a much smaller change in drought using the Penman-Monteith equation. The estimated yearly drought increase was only half as severe as that derived from the Thornthwaite equation. The weather records invariably contain some errors, but Sheffield says those errors don’t alter the conclusion that the simpler model overestimates rises in global drying.
The finding comes in stark opposition to the results of several recent studies. “It presented a somewhat different view of the drying trend for the last 60 years,” says Aiguo Dai, an atmospheric scientist at the State University of New York at Albany, whose own research suggests that the two equations yield very little difference in drought estimates. Dai says the new study fails to consider trends in soil moisture and other variables. He also claims that the new study relies on outdated weather records and questionable radiation data. However, Sheffield and colleagues attribute the disagreement to inconsistencies in the weather data used by Dai and others.
“I think the jury’s still out on why those groups looking at similar metrics come to different conclusions,” says paleoclimatologist Kevin Anchukaitis of the Woods Hole Oceanographic Institution in Massachusetts, who was not involved in either study.
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