A drought is defined as “a lack of precipitation over an extended period of time (usually a season or more), resulting in a water shortage.” Drought indicators include precipitation, temperature, streamflow, ground and reservoir water levels, soil moisture, and snowpack.
A new study has linked subtle changes in Australia’s wettest weather to the occurrence of drought. Dr. Tess Parker of the Australian Research Council Centre of Excellence for Climate Extremes at Monash University led the study, which found that a few days less of heavy rainfall per year contributed to severe drought.
The study comes as the State of the Climate report, released today, indicates a long-term decrease in rainfall in southern Australia. The authors used 120 years of rainfall data from Australia to show that the absence of just 3-5 heavy rainfall days was typically responsible for well over half of the rainfall decline during previous droughts.
Droughts typically break in spectacular fashion because those heavy rain days return to excess, rather than just returning to normal. This shows that drought-breaking rains can also be down to relatively few, but heavy, rainfall events.
Dr. Parker
“The majority of the rainfall comes from these heavy rainfall days (above 20 mm/day), which are typically only 1-2 weeks’ worth of annual rainfall, if not less,” Dr. Parker explained. “However, it is the slight reduction in heavy rain, equivalent to around five or fewer days per year on average, that is responsible for the majority of the rainfall decline across Australia during previous droughts.”
The study also shows that when droughts end, it is due to the return of these days of heavy rain. However, they frequently result in wetter-than-normal conditions.
“Droughts typically break in spectacular fashion because those heavy rain days return to excess, rather than just returning to normal. This shows that drought-breaking rains can also be down to relatively few, but heavy, rainfall events,” Dr. Parker said.
“In wetter climates, like on the east coast, it’s days with rainfall above 50 mm that make the biggest difference.”
Dr. Parker described the significance of the result lies in the links that can be made to rain-bearing weather systems that cause the heavy rainfall that make and break droughts.
“Our study has isolated the importance of days of heavy rainfall for drought development and recovery. Now this is known, we can begin to investigate the types of weather systems related to these heavy rainfall days, which will reveal a lot about important meteorological processes that send us into and out of drought,” Dr. Parker said.
According to the BOM, of all the climate challenges to afflict Australia, drought is one of the most feared, and costly. Much of southern Australia experienced a prolonged Millennium drought 1997–2010. Apart from crop failure and stock loss, droughts set the scene for bushfires, dust storms, and land degradation.
“Effective monitoring and prediction is required to manage and mitigate the socioeconomic effects of drought. This requires knowledge of how droughts begin, develop and recover, and the underlying processes related to these stages of drought,” Dr. Parker said.
