Waterways do not have an unlimited ability to recover from drought, new research shows...
The general view is that waterways, such as rivers and underground water sources, will eventually recover after severe drought and resume their normal flow when the rains return. But new research from Australia pours cold water on that theory.
By analysing 30 years' of rainfall and flow data from 161 water catchments in a part of south-east Australia covering an area about the size of the United Kingdom, researchers from Monash University discovered that one-third of these water catchments had not recovered after almost eight years.
“We found out that 100mm of rain before the drought would have produced more streamflow than the same 100 mm after the drought. So less rainfall is being funnelled into the rivers after the drought and they appear stuck in this low stream flow behaviour,” explains Tim Peterson, one of the authors of the new study, which was published in the journal Science.
If the rain is not flowing down into the rivers or underground water sources, where has the water gone?
“It appears that trees are able to hold onto this rain more tightly than they did before the drought and they are sending it up into the atmosphere,” says Peterson.
The effect is unlikely to be unique to Australia, and the team speculate that it is in fact happening worldwide as similar behaviour has been noticed in waterways in China, Chile and the United States. And with the ever-present threat from climate change, understanding how waterways recover from drought is becoming even more important.
There may, nonetheless, be reason for optimism. According to Peterson, the waterways may yet recover, "our catchments that have not recovered probably will. We just don’t know when they will or how. There is some threshold that has to be crossed before they will recover, so for example, a really wet year or two.”
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