Global drought extent unchanged for past 60 years

THURSDAY, NOVEMBER 15, 2012: Global drought areas have not increased over the past 60 years due to climate change according to a new paper published in Nature, contradicting previous research showing statistically significant increases.

The authors of the paper, Little change in global drought over the past 60 years (doi:10.1038/nature11575), achieved their results after using more realistic calculations based on underlying physical principles behind droughts.

“Many climate change researchers use the Palmer Drought Severity Index (PDSI) and calculate evaporative demand as a sole function of temperature” said a chief investigator at the ARC Centre of Excellence for Climate System Scientist Dr Michael Roderick, one of the study’s co-authors along with Princeton University researchers, Dr Justin Sheffield and Prof Eric Wood.

“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.

“Our results may also help explain why the tree ring data at high latitudes and elevations has diverged from the PDSI drought record during the period of the instrumental record.”

To get a more realistic calculation of drought areas based on the underlying physical principles, the researchers used a standard formula where evaporation depends on sunlight, humidity and wind-speed as well as the temperature.

When the researchers introduced these additional physical characteristics to determine drought area, the results showed no statistically significant increase in global drought between 1950-2008.

“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,” Dr Roderick said.

“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.”

Dr Roderick said, it is time to stop using simplified drought indices in research because it was known to be biased and this had implications for how extremes and changes in the hydrological cycle over land are interpreted.

“It is important that we gain our perspective of the impacts of climate change based on the best physical understanding of processes possible.”


For further information or to interview Dr Michael Roderick contact:
Alvin Stone
Ph: 9385 8953. Mbl: 0418 617 366

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