SEQ drought likely caused by ‘climate variability’

“We found that, unlike in South-West Western Australia, climate change plays little part in the SEQ rainfall reduction, but cannot be ruled out,” Dr Cai said.

The research team aimed to determine whether the SEQ’s recent rainfall reductions were partly due to climate change and, if so, whether dry conditions will occur there more often in the future.

“At this stage, renewal of a rain-generating process with La Niña bringing higher rainfall to SEQ might be expected to last for 10 to 20 years,” Dr Cai said.

“Ongoing research is examining whether increased temperatures linked to climate change in the future will alter the frequency, intensity, and duration of drought. We are also investigating if the rising temperature due to climate change has played a part in the unprecedented low water storage level of the recent drought and how climate change will impact on climate variability.”

The study centred on the contribution to rainfall by naturally occurring events such as El Niño and La Niña, as well as a longer-lasting feature called the Interdecadal Pacific Oscillation (IPO), and how these events may be influenced by future climate change.

SEQ is one of the wetter regions in Australia due to its proximity to the world’s most intensive rainfall-band, located in the Western Pacific. The rain-band, which is powered by the warmest ocean surface temperature on the globe, moves eastward during El Nino tending to decrease SEQ rainfall. During La Nina, the rain-band moves westward leading to increased rainfall in SEQ. Many of the wettest years for the region occurred in La Nina years such as 1956, 1971, and 1974.
 
Much of the regional annual rainfall is recorded in summer. In recent decades, SEQ summer rainfall has been significantly reduced. Up until the drought breaking 2010 La Niña event, the SEQ water storage level dropped to below 20 per cent, the lowest level on record since data collection began in 1890.

The El Niño-La Niña relationship oscillates over several decades, in tandem with the IPO, which has a somewhat similar pattern to the El Niño-La Niña cycle but on a longer time scale. 

“Since 1980, the IPO has been in a phase similar to El Niño – limiting the rainfall that La Niña brings to SEQ as a major rain-generating mechanism,” Dr Cai said.

“This is largely responsible for the recent drought.”

As of 2010, the IPO appears to be moving to a phase similar to La Niña.

Taking the average of results from a set of climate models is the most effective way of ‘distilling’ a climate change signal. The science team assessed the role of climate change by using the same 24 models used by the Intergovernmental Panel on Climate Change.

Their results show that the recent drought in SEQ is not consistent with climate change projected by the models.

Funded by the SEQ Urban Water Security Research Alliance, the study’s findings were published recently in the American Meteorological Society’s Journal of Climate.