While this is a bit dated, from late last year, given all the attention given to the floods in Queensland supposedly being caused by global warming aka climate change, this seemed relevant to review. h/t to reader Baa Humbug and Andrew Bolt
“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.
Here’s the paper:
Cai, Wenju, Peter van Rensch, Tim Cowan, Arnold Sullivan, 2010: Asymmetry in ENSO Teleconnection with Regional Rainfall, Its Multidecadal Variability, and Impact. J. Climate, 23, 4944–4955.
Asymmetry in ENSO Teleconnection with Regional Rainfall, Its Multidecadal Variability, and Impact
Wenju Cai, Peter van Rensch, Tim Cowan, and Arnold Sullivan
CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia
Abstract An asymmetry, and its multidecadal variability, in a rainfall teleconnection with the El Niño–Southern Oscillation (ENSO) are described. Further, the breakdown of this relationship since 1980 is offered as a cause for a rainfall reduction in an ENSO-affected region, southeast Queensland (SEQ). There, austral summer rainfall has been declining since around the 1980s, but the associated process is not understood.
It is demonstrated that the rainfall reduction is not simulated by the majority of current climate models forced with anthropogenic forcing factors. Examination shows that ENSO is a rainfall-generating mechanism for the region because of an asymmetry in its impact: the La Niña–rainfall relationship is statistically significant, as SEQ summer rainfall increases with La Niña amplitude; by contrast, the El Niño–induced rainfall reductions do not have a statistically significant relationship with El Niño amplitude. Since 1980, this asymmetry no longer operates, and La Niña events no longer induce a rainfall increase, leading to the observed SEQ rainfall reduction. A similar asymmetric rainfall teleconnection with ENSO Modoki exists and shares the same temporal evolutions.
This breakdown is caused by an eastward shift in the Walker circulation and the convection center near Australia’s east coast, in association with a post-1980 positive phase of the interdecadal Pacific oscillation (IPO). Such a breakdown occurred before 1950, indicating that multidecadal variability alone could potentially be responsible for the recent SEQ rainfall decline. An aggregation of outputs from climate models to distill the impact of climate change suggests that the asymmetry and the breakdown may not be generated by climate change, although most models do not perform well in simulating the ENSO–rainfall teleconnection over the SEQ region.