UN IPCC prize winning report in error about drought claims says Nature study. PDSI not intended to track long term trends, PDSI long known unreliable in this area

11/19/12, "Study: Drought Trends, Estimates Possibly Overstated Due To Inaccurate Science,
" washington.cbslocal.com

"An index frequently used by scientists to predict drought trends – trends whose increased frequency and intensity were blamed on global warming – may have been misused, resulting in possibly inaccurate findings.

The Palmer Drought Severity Index is primarily used by scientists to keep track of short-term drought trends. Researchers at Princeton University have now found that the index may not properly reflect what’s to come.

“[C]alculations of the Palmer Drought Severity Index (PDSI) show a decrease in moisture globally since the 1970s with a commensurate increase in the area in drought that is attributed, in part, to global warming,” the published paper states. “The simplicity of the PDSI, which is calculated from a simple water-balance model forced by monthly precipitation and temperature data, makes it an attractive tool in large-scale drought assessments, but may give biased results in the context of climate change.”

The findings were published Thursday in the journal Nature, whose offices are located in Washington, D.C."...

[Ed. note: Nature Magazine is owned by Macmillan Publishing Co. which is based in London, England.]

(continuing): "Study co-author Eric Wood, who also serves as a professor of civil and environmental engineering at Princeton University, was quoted as saying that the results make it seem as though “it will never rain again,” according to the Christian Science Monitor.

Wood authored the paper with another Princeton University researcher, Justin Sheffield.
The PDSI is reportedly the source from which drought maps are made – usually colored in brown, red or yellow, depending on drought severity.

The Christian Science Monitor learned from Wood that the PDSI was not intended to track long-term trends, and that its simplicity may lead to skewed results when applied to future times.

“We’ve known for quite a long time that the PDSI calculation is prone to problems dealing with climate change,” added Columbia University drought and climate researcher Richard Seager to the website. “Rising temperatures drive it haywire.”

The study noted in Nature that “[m]ore realistic calculations, based on the underlying physical principles that take into account changes in available energy, humidity and wind speed, suggest that there has been little change in drought over the past 60 years.
”" via Climate Depot





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