The Recent Victorian Drought and its Impact Without precedent? MARCH 2013 RIRDC Publication No. 12/040 The Recent Victorian Drought and its Impact Without precedent? By Keely Mills, Peter Gell and Peter Kershaw March 2013 RIRDC Publication No. 12/040 RIRDC Project No. PRJ-005440 © 2013 Rural Industries Research and Development Corporation. All rights reserved. ISBN 978-1-74254-481-6 ISSN 1440-6845 The Recent Victorian Drought and its Impact. Without precedent? Publication No. 12/040 Project No. PRJ-005440 The information contained in this publication is intended for general use to assist public knowledge and discussion and to help improve the development of sustainable regions. You must not rely on any information contained in this publication without taking specialist advice relevant to your particular circumstances. While reasonable care has been taken in preparing this publication to ensure that information is true and correct, the Commonwealth of Australia gives no assurance as to the accuracy of any information in this publication. The Commonwealth of Australia, the Rural Industries Research and Development Corporation (RIRDC), the authors or contributors expressly disclaim, to the maximum extent permitted by law, all responsibility and liability to any person, arising directly or indirectly from any act or omission, or for any consequences of any such act or omission, made in reliance on the contents of this publication, whether or not caused by any negligence on the part of the Commonwealth of Australia, RIRDC, the authors or contributors. The Commonwealth of Australia does not necessarily endorse the views in this publication. This publication is copyright. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. However, wide dissemination is encouraged. Requests and inquiries concerning reproduction and rights should be addressed to the RIRDC Publications Manager on phone 02 6271 4165. Researcher Contact Details Peter Gell Centre for Environment Management, School of Science, Information Technology & Engineering, University of Ballarat, VIC 3353, Australia. [email protected] In submitting this report, the researcher has agreed to RIRDC publishing this material in its edited form. RIRDC Contact Details Rural Industries Research and Development Corporation Alan Davey, Senior Research Manager Level 2, 15 National Circuit BARTON ACT 2600 PO Box 4776 KINGSTON ACT 2604 Phone: 02 6271 4100 Fax: 02 6271 4199 Email: [email protected]. Web: http://www.rirdc.gov.au Electronically published by RIRDC in March 2013 Print-on-demand by Union Offset Printing, Canberra at www.rirdc.gov.au or phone 1300 634 313 ii Foreword Understanding climate change is a critical challenge for managers of natural landscapes and the industries that are supported by them. Southern Australia sits in a climate zone that can respond greatly to variations in effective rainfall. Recent years attest to the impact of severe drought, and flood, brought about by shifts in the major atmospheric circulation patterns that affect the southern half of our continent. The region is also subjected to increasing temperatures, and climate models reveal a high prospect for drier conditions through this century. The capacity to detect subtle, long term trends in climate, such as the incidence of drought, is challenged by the high level of natural variability in our climate. Analyses that rely largely on memory, or even the instrumental record, are limited in the extent to which they can qualify recent climate extremes. This can be overcome by extending the instrumental record many centuries, and even millennia, from archives such as tree rings, speleothems, corals and the sediments that accumulate regularly over time. This provides the context, and benchmark, against which the conditions most familiar to us, the present and recent past, can be compared. In preparing for the future, the most appropriate measures are informed by an understanding of the risk of extremes and the present trajectory and rate of change. This is especially critical for all involved in rural industries, from those engaged in writing the policy settings, to those making decisions of land use at the individual farm level. This project has sought out the sediment records from lakes that are most likely to be responsive to the past variations in effective moisture, such as past drought events, and analysed them to quantify climate variation over thousands of years to the highest practical resolution. It is clear that there have been several severe, long lasting droughts over the last 5000 years, and that they have resulted in considerable change to the ecology of lakes. This report considers the evidence that, at the millennial scale, the present state of lakes is highly unusual, if not unprecedented. While there is strong evidence that the recent condition of the lakes is, at least in part, a consequence of direct catchment disturbance, this report presents evidence that the level of effective rainfall over the last 40 years, and particularly since 1997, is unusual, and possibly unprecedented, relative to the last 5000 years. With the strong evidence provided by this report at hand, it is very difficult to imagine a future where the trajectory of existing industries, current rural practices and the delineation of food-producing regions within our continent, does not change dramatically. This report is an addition to RIRDC’s diverse range of over 2000 research publications and it forms part of our Dynamic Rural Communities R&D program, which aims to enhance the capacity of rural communities to manage economic, social and environmental change. Most of RIRDC’s publications are available for viewing, free downloading or purchasing online at www.rirdc.gov.au. Purchases can also be made by phoning 1300 634 313. Craig Burns Managing Director Rural Industries Research and Development Corporation iii About the Authors Peter Gell Peter Gell is the Associate Dean for Research within the School of Science, Information Technology and Engineering and the Director of the Centre for Environmental Management at the University of Ballarat. Peter has 25 years’ experience as a palaeoecologist including projects examining the impact of forest harvesting in East Gippsland and of land and water use on wetlands of the Murray Basin. He is currently examining the long-term human impact on Australian ecosystems and the impact of people and climate change on the world’s lake ecosystems. He has published numerous articles, produced over 20 industry reports and lead projects understanding climate and waterway change in Brazil, France, China and across Australia. Using short term palaeoecology he has established environmental baselines, conducted biomonitoring to assess wetland and stream water quality over time, and geochemical and macro fossil analysis to infer the source of nutrients, sediments and changing trophic structure, macrophyte and invertebrate biota. He has a broad understanding of climate and climate change, hydrology, wetland biota and water sediment chemistry. His strength is his capacity to integrate these disciplines to understand river and wetland functioning in the past, present and future. Peter Kershaw Peter Kershaw is currently a Professor Emeritus and Director of the Centre for Palynology and Palaeoecology in the School of Geography and Environmental Science at Monash University. Since 1970 he has published over 150 peer-reviewed papers and 16 co-authored books or journal special issues and supervised 25 PhD students in the general area of the vegetation and environmental history of Australasia and South-east Asia, with particular emphases on peatland and rainforest dynamics, the timing of arrival and impact of indigenous people, biomass burning and climate change and variability. This research was supported continuously by the Australian Research Council for over 30 years. He is Vice-President of the International Quaternary Association's Palaeoclimate Commission and is an Editor-in-Chief of the Elsevier journal Palaeogeography, Palaeoclimatology, Palaeoecology. Keely Mills Keely Mills is a Post-Doctoral Research Associate within the Centre for Environmental Management at the University of Ballarat. Since her Honours research in 2003 she has been involved in the analysis of sediment records for biological proxies in order to understand past changes environmental changes. Her research focus for her PhD involved the use of fossilised algae (diatoms) from lake sediments in Uganda to reconstruct past changes in rainfall and human impacts as well as the development of quantitative diatom models (transfer functions) to reconstruct changes in water chemistry parameters in a variety of lake systems. In 2009 Keely moved to Australia to undertake research on the diatom records from the volcanic lakes of western Victoria in order to understand drought history over the last 2000 years. iv Acknowledgments This study was funded by the Rural Industries Research and Development Corporation (RIRDC; 2009-2011) and Land Water Australia (LWA; 2008-2009). This research would not have been possible without the assistance and skills of a number of researchers in Australia, New Zealand and the United Kingdom. First and foremost, sincere thanks are extended to Dr Merna McKenzie (Monash University) who completed the pollen counts on three of the lake sediment cores contained within this report (Lakes Colac, Purrumbete and Burn) and Tara Lewis (PhD Candidate, Monash University) for her