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Link between warming and past droughts questioned

January 7, 2013

A series of recent droughts from Australia to the United States has led some scientists to warn that global warming has already begun to increase worldwide drought. But new research from Princeton and the Australian National University in Canberra has found that this might not be the case.

The theory that increased temperature would lead to more rapid evaporation and increase the frequency and severity of droughts seems logical. As the Intergovernmental Panel on Climate Change (IPCC) reported in 2007, “more intense and longer droughts have been observed over wider areas since the 1970s.”

But the new research indicates that the development of drought is much more complex than previously thought and that the reports of increasing drought were caused by weaknesses in the mathematical model used to simulate drought rather than any real drying trend.

“The overall view has been that as temperature increases drought is going to increase,” said Justin Sheffield, a research scholar in Princeton’s Department of Civil and Environmental Engineering. “But it is not that simple.”

A new analysis of drought conditions over the past 50 years has yielded a nuanced view of global trends. Red areas have experienced increasing levels of drought while blue areas have become less prone to dry conditions. Overall, there has been less of a trend toward drought globally than previously thought, Princeton researchers have found. (Image courtesy of Justin Sheffield)

In an article published in November in the scientific journal Nature, the researchers reported that errors resulting from a model commonly used to assess drought, the Palmer Drought Severity Index, had led to overestimates of the severity of drought worldwide. Besides Sheffield, the paper’s authors were Eric Wood, the Susan Dod Brown Professor of Civil and Environmental Engineering at Princeton, and Michael Roderick, a professor in the Research School of Earth Sciences and the Research School of Biology at Australian National University.