Abstract/Summary

Queensland’s climate experiences considerable natural inter-annual and decadal variability in its rainfall. To determine how Queensland's rainfall is going to change in the coming decades as the planet warms, it is critical to establish which global and regional climate phenomena are driving this variability. Understanding the potential impacts of climate change is essential to inform strategies and actions to avoid or manage dangerous levels of change. The impacts of these changes are important especially for those sectors that are vulnerable to changes in rainfall, such as water-resource management and agriculture. In 2007, the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC, 2007) confirmed that there is currently substantial uncertainty in rainfall projections for the Australian region for the coming century. This reinforces the urgent need to reduce that uncertainty. Improving the current understanding of key processes and phenomena that influence Queensland rainfall on timescales from days to decades will help to address that uncertainty, as there may be greater confidence in the impacts of climate change on these phenomena than for rainfall. A reduced uncertainty in rainfall changes would support effective planning to address potential changes in the hydrological cycle at the regional and local level. Part of the uncertainty in future rainfall changes arises from the various competing and interacting influences on Queensland rainfall, which are associated with synoptic and climate drivers across various time scales, such as tropical cyclones, the Madden-Julian Oscillation (MJO), the El-Niño Southern Oscillation (ENSO) and the Inter-decadal Pacific Oscillation (IPO). The MJO controls the sub-seasonal variations in the summer monsoon rainfall with a period of 30-60 days. It primarily affects northern Queensland and modulates the monsoon and trade-wind circulations. Active periods of the MJO also increase the probability of tropical cyclone formation in the Coral Sea. On inter-annual timescales, Queensland's rainfall is heavily influenced by ENSO: wet conditions prevail in La Niña (cold equatorial Pacific Ocean temperatures) years, while El Niño (warm equatorial Pacific Ocean temperatures) promotes drought. Rainfall is sensitive to both the magnitude and position of El-Niño and La Niña events. Central Pacific ENSO events have a much stronger impact on Queensland than eastern Pacific events. The link between Queensland's rainfall and the ENSO can fluctuate from one decade to the next, but shows no long-term trend. The IPO describes the slowly evolving variations in Pacific Ocean temperatures, with a period of about 20-30 years. Its positive (warm) phase resembles an expanded El-Niño, while its negative (cool) phase resembles an expanded La Niña. El-Niño and La Niña events canoccur in either phase of the IPO. The IPO influences the relationship between ENSO and Queensland rainfall: warm phases show a weak connection, while cold phases display a strong connection. Knowledge and prediction of the influence of these drivers on regional and local rainfall will help improve the understanding of climate changes at those smaller scales. This may also result in more-accurate predictions of climate variability and change over the next 20 years - a key period for climate-change adaptation efforts. This report reviews existing studies of observed changes in Queensland rainfall - its mean, variability and extreme events - to determine the dominant remote synoptic and climate drivers of rainfall. The review found that although many studies have described variations in rainfall in Queensland and across Australia, only a few have explained these changes as due to variations in the impact of known remote rainfall drivers. Even fewer studies have provided plausible physical mechanisms for the variability in the influence of those drivers. Analysis has often focused on annual-or seasonal-mean rainfall, neglecting the spatial and temporal characteristics of rainfall. Little research had been undertaken on the interactions between temporal scales of variability, despite strong indications that these interactions are key to determining the character of Queensland’s rainfall.