Drought areas not expanding finds ANU
The total global area affected by drought has not expanded over the past 60 years, according to new research released by the Australian National University (ANU).
The findings contradict earlier research, and are a result of more realistic calculations based on the underlying physical principles behind droughts.
ANU’s Dr Michael Roderick, from the Research School of Earth Sciences, said that more accurate research and led to a better understanding of global drought conditions.
“Many climate change researchers use the Palmer Drought Severity Index (PDSI) and calculate evaporative demand as a sole function of temperature,” said Dr Roderick.
“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.”