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A new study analyzing flooding in Australia is providing some of the first direct evidence that major flooding events have been on the rise over the past century.
In their paper, researchers Scott B. Power, the head of climate research at Australia’s Bureau of Meteorology, and Jeff Callaghan, a retired meteorologist, show that on one 1,500-kilometer stretch of southeast Australia’s coast, the frequency of major floods has nearly doubled since the mid-19th century. Though they stop short of tying the increase in flooding to anthropogenic climate change, the findings may be the first definitive step in confirming the expected link.
“To test that hypothesis, you need the actual data, and it turns out that [having] long-term data … is a pretty rare feat,” says Power. “This is the longest [flood record] for Australia and the Southern Hemisphere that I’m aware of, and probably one of the longest in the world.”
Long-term, reliable flood records are essentially nonexistent for many areas of the world. Answering questions about changing flood frequencies without such records is impossible, and scientists currently have “low confidence” in even basic observations, the authors say in their report.
But by analyzing a database of major floods along Australia’s heavily-populated southeastern coast—compiled through decades of work from instrumental data like rainfall records to newspaper articles—Power and Callaghan found that, since 1860, there has been an increase from an average of 1.3 major floods per year in the first half of the record, to two major floods in the latter half.
The database, which Power and Callaghan first published in 2014, considers a major flood to be an inundation of a river within 50 kilometers of the coast or flooding overland near the coast. The study covers an area stretching from Brisbane to Eden, and includes major centers such as Sydney and Gold Coast.
Though the scientists found regional variations in flood activity, most parts of the study area also saw an increase in extreme precipitation over the past century, which Power and Callaghan point to as a significant contributor to the increase in flooding.
More intense and more frequent precipitation is an expected consequence of climate change for most mid-latitude and tropical regions, according to the most recent Intergovernmental Panel on Climate Change report. If the trends are connected, other regions may very well see the same uptick in severe floods as documented in southeastern Australia.
Power and Callaghan provide nine possible explanations for the increase in major floods, including naturally occurring climate variability, anthropogenic warming, and land-use changes, among others. Ultimately, however, they conclude that there just isn’t enough evidence yet to point to how much of a role climate change has contributed to flooding in the region.
“It’s very difficult to explain the trend just in terms of internal climactic variability,” Power says. “If global warming has been a factor, we don’t know what the magnitude of that influence has actually been. So this is the first step [in figuring that out.]”