According to Anna Salleh of ABC News Australia the researchers report in their study that the 2007 4th Assessment Report (AR4) by the UN Intergovernmental Panel on Climate Change (IPCC) “overestimated” reports of an increase of drought conditions throughout the world. That report had claimed that droughts had increased in intensity and duration, and had been observed in more and more locations, especially in the tropics and subtropics, Salleh explained.
The IPCC report was compiled using information from the Palmer Drought Severity Index (PDSI), which lead author Dr Michael Roderick of the Australian Research Council (ARC) Centre of Excellence for Climate System Science and colleagues said is flawed.
“Many climate change researchers use the Palmer Drought Severity Index (PDSI) and calculate evaporative demand as a sole function of temperature,” Dr. Roderick said in a statement. “The use of the PDSI has led to a bias in results that indicated an increase in the area of global drought where none has actually occurred.”
“It is curious that the long term use of the PDSI by climate impact researchers has persisted, when it has been recognized repeatedly as not being a realistic indicator of historical drought conditions,” he added. “Even the section on droughts in the IPCC AR4 report was substantially revised by the more recent IPCC report on extremes because of its over reliance on the PDSI and the potential for overestimating the increases in global and regional drought.”...
A strip of vegetation along the aryk (a channelled creek that flows from the mountains (in the background)) in the desert outside of Tamchy, Kyrgyzstan. Shot by Vmenkov, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license
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