Research shows global drought areas have not increased

The findings are the result of the paper’s authors using more realistic calculations based on the underlying physical principles behind droughts.
 
Dr Michael Roderick, from the Research School of Earth Sciences in the ANU College of Physical and Mathematical Sciences and the Research School of Biology in the ANU College of Medicine, Biology and Environment, also a chief investigator at the ARC Centre of Excellence for Climate System Science, co-authored the study with Princeton University researchers Dr Justin Sheffield and Professor Eric Wood.
 
"Many climate change researchers use the Palmer Drought Severity Index (PDSI) and calculate evaporative demand as a sole function of temperature," Dr Roderick said.
 
"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 make a more realistic calculation of drought areas based on the underlying physical principles of drought, 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 areas between 1950 and 2008.
 
"It is curious that the long-term use of the PDSI by climate impact researchers has persisted, when it has been recognised repeatedly as not being a realistic indicator of historical drought conditions," Dr Roderick said.
 
"Even the section on droughts in the Intergovernmental Panel on Climate Change (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.