Climate Dynamics

, Volume 26, Issue 7–8, pp 765–780 | Cite as

Projected future changes in synoptic systems influencing southwest Western Australia

Article

Abstract

Rainfall in the southwest of Western Australia (SWWA) is sensitive to shifts in the hemispheric scale circulation due to its location at the northward extent of the influence of mid-latitude fronts. A step-drop in the 1970s to a new winter rainfall regime has caused great concern for water users in the region. The synoptic systems at the height of winter in the latter half of the 20th century over this region have been described in Hope et al. (Clim Dyn, 2006) using a self-organising map, and in this study the projected future shifts in those systems has been examined. Bounds are placed on the possible responses by examining a number of different models and, into the future, two scenarios at the upper (SRES A2) and lower (SRES B1) limits of plausible human induced emissions. Rainfall taken directly from the models captures the rainfall decline in the 1970s, and, although it is not as large as observed in any one model, all the models express a decline, which is a very strong result. Into the future the rainfall decline is dramatic. The scenario at the upper bound of emissions, where atmospheric concentrations of greenhouse gases continue to rise strongly, shows a rainfall decline right through to the end of the century. The shift in synoptic systems for most models is to far fewer troughs and more high pressure systems across the region. One model exhibits a different signature, with a shift to more systems with a zonal structure. The fact that there is a rainfall decline shown by all models, yet the synoptic changes are different, highlights how sensitive SWWA rainfall is to the different responses of climate models to increasing greenhouse gases. In the B1 scenario, the concentrations rise only slowly in the second half of the century and the shift is still to drier conditions, but it is not as striking. These results show that increasing concentrations of greenhouse gases lead to increasingly dry conditions in SWWA, and as the atmospheric concentrations rise, the synoptic response intensifies.

Notes

Acknowledgements

This research was supported by the Indian Ocean Climate Initiative (IOCI). Thank you to Aurel Moise (BMRC) and Julie Arblaster (NCAR, BMRC) for obtaining the IPCC model output and Zhihong Li (BMRC) for pre-processing some of the data. I also thank Julie Arblaster for calculating the anomalies of precipitable moisture in the models and guiding me on the range of forcing in the 20C3M simulations. Scott Power, Neville Nicholls, Julie Arblaster and Debbie Hudson, all from BMRC, provided helpful comments. I acknowledge the international modelling groups for providing their data for analysis, the Program for Climate Model Diagnosis and Intercomparison (PCMDI) for collecting and archiving the model data, the JSC/CLIVAR Working Group on Coupled Modelling (WGCM) and their Coupled Model Intercomparison Project (CMIP) and Climate Simulation Panel for organizing the model data analysis activity, and the IPCC WG1 TSU for technical support. The IPCC Data Archive at Lawrence Livermore National Laboratory is supported by the Office of Science, US Department of Energy.

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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  1. 1.Bureau of Meteorology Research CentreMelbourneAustralia

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