The first and most common definition of a “drought” is a period of heavy rainfall, the National Drought Mitigation Centre said in its 2017 annual report.
The report said there was “no consensus” on the definition of “extreme” drought.
A 2015 report by the Australian Bureau of Meteorology, which was published in the Australian Journal of Meteorological Sciences, found the definition “has little basis in scientific reality”.
It also said it was “unlikely” to have any practical impact on water conservation or infrastructure development in Australia.
“Drought is a relatively new phenomenon and a complex phenomenon,” it said.
“It has often been referred to as a ‘complex weather system’ or ‘climate change phenomenon’ but the definition that has become most widely accepted has only recently become a useful tool for assessing the risk of extreme events.”
The report from the National Centre for Drought Prediction and Research also noted there was no consensus on the precise definition of an extreme drought, saying it was unlikely to have a useful impact on any of the six factors that were identified by the World Meteorological Organisation.
It also warned that a lack of agreement among scientists on the scope and severity of drought was not conducive to a “flexible assessment of a severe drought”.
“There are very few independent scientific assessments of drought risk, and the number of independent assessments is low,” the report said.
A spokesman for the Australian National University said the definition could lead to a misunderstanding of the risk to water supplies.
“The definition of drought is not in line with what we would expect from a natural system, and it’s not an assessment of how much damage we might be looking at in the short term,” he said.
The study found there was a lack to know what the impacts of drought would be.
The first thing you want to know is the magnitude of the impacts and if there’s a drought.
The second thing you should know is whether there’s any impact on the water cycle and whether there are any impacts on agricultural water use or on groundwater use.
The third thing you need to know, if you’re going to say a drought is severe, is whether you’re saying that the drought has caused significant losses of water or is it an increase in the volume of water in the environment?
That’s where a lot of uncertainty exists.
Dr David Dutton, from the University of Queensland’s Climate Change Institute, said the lack of consensus in the scientific community meant there was little incentive for governments to make decisions on whether to conserve water.
“There’s no consensus, and you have no mechanism for people to actually try to make informed decisions,” Dr Dutton said.
He said while the World Bank was looking into the definition, it was likely the definition would be used by the National Institute for Water and Atmospheric Research to gauge whether it would be an extreme event.
“I would think it would come down to a bit of a consensus between the various bodies that are involved,” he told ABC Radio National.
The Australian Water Agency’s Dr David Williams said while drought was a “complex phenomenon” and could lead, for example, to the loss of trees or a loss of fish stocks, the “droughts” that occurred in the past were rare.
“We don’t have a long record of extreme drought,” he added.
“But we do have a lot more records of extreme weather events.”
Dr Williams said it would likely be decades before drought was seen as a serious threat in Australia, but said that the National Environment Agency was working on a tool that could help monitor water consumption and conserve water resources.
“People need to be very aware that drought is a real and serious problem that impacts on water and land use, it impacts on agriculture and water quality, and its a very complex phenomenon that we don’t yet have a good understanding of,” he was quoted as saying.
“And as a consequence we are not seeing a lot in the way of significant changes in water use and water storage.”
