“The calculations that have all been done assumed that the only thing that controls how hard the atmosphere sucks water up is the temperature of the air, and that’s not true.”—Prof Roderick. Image: Hume Lake in VIC, Tim KeeganWHILE drought in WA’s south-west continues to worsen, a new analysis of global drought shows that, worldwide, the problem has been overestimated for decades.
Three of the world’s leading drought experts this month published a paper in the peer-reviewed journal Nature, showing that reports of more intense, longer droughts since the 1970s are incorrect.
The scientists, including Australian Research Council’s Michael Roderick of the Centre of Excellence for Climate System Science, found that historical modelling calculations were too simplistic and ignored important factors that contribute to drought.
“We show that the previously reported increase in global drought is overestimated because the Palmer Drought Severity Index uses a simplified model of potential that responds only to changes in temperature, and thus responds incorrectly to global warming in recent decades,” Associate Professor Roderick says.
“The calculations that have all been done assumed that the only thing that controls how hard the atmosphere sucks water up is the temperature of the air, and that’s not true.”
“More 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,” the scientists report in Nature.
Prof Roderick says that while the south-west pocket of WA—as far north as Geraldton—continues to dry, the rest of WA, including its deserts, is getting wetter.
“The trend in wetness there [in the desert] is one of the biggest in the world,” he says.
“The drying in the south-west [pocket] is not big by world standards.”
Prof Roderick and his team found that some areas had suffered more drought since the 1950s, such as sub-Saharan Africa. But in other areas, the amount of drought has declined or stayed constant.
The Intergovernmental Panel on Climate Change (IPCC), consisting of hundreds of the world’s best climate scientists, originally used the Palmer Drought Severity Index in its Fourth Assessment Report (AR4).
The IPCC has since documented its over-reliance on the PDSI in regard to drought.
University of Leeds climate change professor Piers Forster has backed the Roderick study and the IPCC’s AR4.
“This study is a good example of the way scientists are continually questioning and refining our assessment of past and future climate changes.
“This study in no way invalidates the overall conclusions of the IPCC AR4 study,” he says.
Prof Roderick says the relationship between climate change and drought is tenacious at best.
