Major flooding events follow 40-year cycle in south-east Queensland, study suggests.
The next serious widespread south-east Queensland flooding event could happen in 2050, according to an analysis of historical flood data for the region.
Using Bureau of Meteorology’s Australian flood data across 10 south-east Queensland catchments from 1890-2014, researchers found past major flooding events occurred in a 40-year cycle, with five years of high risk and 35 years of low risk.
The cycles were originally predicted by a small group of engineers from Queensland government departments in the 1980s, who conducted a range of flood studies and development projects following the 1974 Brisbane flood.
The group evaluated historical gauge data and discovered three large flooding events in 1893, 1931 and 1974 across the south-east Queensland region, according to a research paper published in Australasian Journal of Water Resources on Monday.
University of Newcastle Associate Professor and co-author Anthony Kiem said he was approached by co-author Greg McMahon, one of the engineers and the chief flood expert in Queensland’s local government department in the early 1990s, to determine the possible cause of these cycles.
Dr Kiem said the speculation of a 40-year flood cycle had “some credibility” after he found the five-year target periods had an “abnormally higher number of floods” than other periods.
“We have about 125 years in our study period and we had four five-year target periods where based on the speculation you would expect higher floods,” he said.
“Those four five-year periods make up only 16 per cent of the record but they actually contain about 80 per cent of the major floods in south-east Queensland.
“The next serious widespread flooding in south-east Queensland is expected in 2050-54 if this holds true.”
He said sea surface temperature fluctuations and pressure changes in the north and south Pacific Ocean, called interdecadal Pacific Oscillation (IPO), happened in 20- to 40-year cycles and were possibly linked to the major flooding events.
“There has been a lot of work in the last decade linking IPO with rainfall and flood variability and drought variability in Australia,” he said.
“When the IPO is in its negative phase, that is when you get a gathering of warm sea surface temperatures off the east of Queensland,” he said.
“Warmer sea surface temperatures mean evaporation is increased and when you have increased evaporation off the ocean there is more water in the atmosphere … so it rains more often and when it does rain there is more water in the atmosphere to fall.
Originally Published by The Brisbane Time, continue reading here.