Climate variability and change in south-eastern Australia A synthesis of findings from Phase 1 of the South Eastern Australian Climate Initiative (SEACI) South Eastern Australian Climate Initiative • Synthesis report Prepared for South Eastern Australian Climate Initiative Steering Committee Citation CSIRO (2010) Climate variability and change in south-eastern Australia: A synthesis of findings from Phase 1 of the South Eastern Australian Climate Initiative (SEACI) Contributors The following people contributed to the production of this report: Project Leaders – Bryson Bates, Paul Holper, Ian Smith. Project Support Officer – Mandy Hopkins. Project Coordinator – Gemma Ansell. Theme Leaders – Bertrand Timbal, Francis Chiew, Harry Hendon. Project Team CSIRO: Deborah Abbs, Gael Alory, Wenju Cai, Edward Campbell, Tim Cowan, Steve Charles, Francis Chiew, Steven Crimp, Jeff Dunn, Guobin Fu, Paul Holper, Roger Jones, Dewi Kirono, Yun Li, John McGregor, Peter McIntosh, Gary Meyers, Kim Nguyen, Uday Nidumolu, Mark Palmer, Michael Pook, Tony Rafter, James Risbey, David Robertson, Ian Smith, QJ Wang, Ian Watterson, Penny Whetton, Susan Wijffels, Lu Zhang. Bureau of Meteorology (BoM): Oscar Alves, Karl Braganza, Andrew Charles, Elodie Fernandez, Harry Hendon, Zhihong Li, Eun-Pa Lim, Guo Liu, Bradley Murphy, Clinton Rakich, Bertrand Timbal, Guomin Wang, Matt Wheeler. Science Panel – Jason Alexandra (Murray–Darling Basin Authority), Tom Keenan (BoM), Mike Manton (Independent expert), Michael Martin (Department of Climate Change and Energy Efficiency), Rae Moran (Department of Sustainability and Environment Victoria), Graeme Pearman (Independent Chair), Glen Walker (CSIRO). Steering Committee – Campbell Fitzpatrick (DSE VIC), Chris Johnston (DCCEE), Warwick McDonald (CSIRO), Neville Smith (BoM), Jody Swirepik (MDBA). We acknowledge CSIRO communication staff for their assistance with the production of this report. © Copyright Commonwealth Scientific and Industrial Research Organisation (CSIRO Australia), 2010 Important notice: All rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO. The results and analyses contained in this Report are based on a number of technical, circumstantial or otherwise specified assumptions and parameters. The user must make its own assessment of the suitability for its use of the information or material contained in or generated from the Report. 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South Eastern Australian Climate Initiative • Synthesis report Climate variability and change in south-eastern Australia A synthesis of findings from Phase 1 of the South Eastern Australian Climate Initiative (SEACI) May 2010 Contents Summary of major findings for policy makers and water managers ...................................................................................1 Executive summary................................................................................................................................................................................2 The South Eastern Australian Climate Initiative – Phase 1 .......................................................................................................4 Major findings ..........................................................................................................................................................................................6 Progress on key science questions .................................................................................................................................................22 Next steps ...............................................................................................................................................................................................28 References ...............................................................................................................................................................................................29 South Eastern Australian Climate Initiative • Synthesis report South Eastern Australian Climate Initiative • Synthesis report South Eastern Australian Climate Initiative (SEACI) Summary of major findings for policy makers and water managers Observed hydroclimatic changes • This provides evidence that observed changes in the large-scale circulation affecting south-eastern • The current 13-year drought in the southern Australia are associated with global warming which Murray-Darling Basin (MDB) and Victoria is is therefore likely to be contributing to the drought. unprecedented compared with other recorded These changes do not account fully for the ongoing droughts since 1900: drought, and it remains likely that natural variability - Being largely constrained to the is also a contributing factor. southern-Australian region; - Having lower year-to-year rainfall variability; there Anticipating the future being no ‘wet’ years through this period; and - The seasonal pattern of the rainfall decline being • The observed changes in the hydroclimatic data maximum in autumn but including losses in may indicate a shift in the climate for south-eastern winter and spring as in previous droughts. Australia. A similar shift in climate evidenced via a reduction of rainfall and streamflow has also been • There has been a 13 per cent reduction in rainfall in experienced beginning in the 1970s in south-west the southern MDB (the Goulburn-Broken, Campaspe, Western Australia. That shift also has been linked to Loddon-Avoca and Wimmera basins) over the period global warming and a range of other factors. 1997-2006 compared with long-term averages, which has led to an extreme decline in modelled • Climate model projections for the coming decades annual streamflow of 44 per cent relative to the indicate an increasing risk of below average rainfall long-term average (1895 to 2006). The streamflow for south-eastern Australia. SEACI research also shows reduction during the current drought period is that short-duration storms may become more intense significantly higher than the reduction during the across the region, especially over the inland plains. World War II drought (23 per cent) and Federation • The current rainfall decline is at least in part drought (27 per cent). This report considers only the attributed to climate change, raising the possibility impact of climate on streamflow (other drivers of that the current dry conditions may persist, and streamflow such as interception and management possibly intensify, as has been the case in south-west activities are not considered explicitly). Western Australia. • It is prudent to plan for conditions that are likely Explaining the changes to be drier than the long-term historical average • Factors that have contributed to this streamflow conditions because the current drought appears decline include the: to be at least partly linked to climate change and - Disproportionate rainfall decline in autumn climate model projections of a drier future across the resulting in dry soil conditions at the start of the south-east. runoff season; • There are questions remaining about how to apply - Rainfall decline in winter-spring when most of the climate change projections given that the recent runoff occurs; observed changes in rainfall and streamflow are - Lack of high rainfall years in the past decade; and larger than the projected changes to mean climate - Higher temperatures. for 2030. Further research is planned for Phase 2 of SEACI aimed at better understanding the relative • The very low autumn rainfall and low winter/spring roles of natural variability and climate change in the rainfall is linked to rising temperatures and associated recent rainfall decline. This will assist in determining changes in the large-scale circulation of the atmosphere. how to best combine the observed climate records These effects are evidenced by the increasing intensity with future projections. of the sub-tropical ridge (the high atmospheric pressure 1 cells that tend to persist across southern Australia and • The SEACI research program has also produced are characteristic of the region’s prevailing climatic improvements to both statistical and dynamical conditions). A climate modelling study showed that approaches to seasonal climate and streamflow the observed intensification of the sub-tropical ridge forecasting. Such improved forecasting will assist can only be achieved when anthropogenic greenhouse resource managers and users to manage water gases are included in climate models. resources in a changing climate. South Eastern Australian Climate Initiative • Synthesis report Executive summary Research in the South Eastern Australian Climate Initiative reduction in modelled annual streamflow in the southern (SEACI) commenced in 2005 to investigate the causes, Murray-Darling Basin (the Goulburn-Broken, Campaspe,