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Global drought may have changed less than thought

Simple models have overestimated drying over past 60 years

4:47pm, November 14, 2012

Droughts shrivel crops, threaten communities, and wither ecosystems. Studies claim global warming is increasing drought worldwide, and may already have done so. But the standard method of assessing drought has exaggerated drying trends over the past 60 years, scientists report in the Nov. 14 Nature.

The 2007 report of the Intergovernmental Panel on Climate Change concluded that “more intense and longer droughts have been observed over wider areas since the 1970s.” Its findings were largely based on a widely used model known as the Palmer Drought Severity Index, which uses temperature and rainfall to determine dryness. Originally developed in the 1960s to help apportion aid to drought-stricken farmers, the index may skew drought trends in the presence of climate change.

“It’s quite obvious that the Palmer model has been overestimating changes in drought,” says study coauthor Justin Sheffield, a hydroclimatologist at Princeton U

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