Extending the Haines Index
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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology Atmospheric Stability Environments and Fire Weather in Australia – extending the Haines Index Graham A. Mills and Lachlan McCaw CAWCR Technical report No. 20 March 2010 Atmospheric Stability Environments and Fire Weather in Australia – extending the Haines Index Graham A. Mills 1,2 and Lachlan McCaw 2,3 1Centre for Australian Weather and Climate Research 2Bushfire Cooperative Research Centre 3 Department of Environment and Conservation, Manjimup. Western Australia CAWCR Technical Report No. 020 March 2010 ISSN: 1836-019X National Library of Australia Cataloguing-in-Publication entry Title: Atmospheric Stability Environments and Fire Weather in Australia – extending the Haines Index [electronic resource] / Graham A. Mills and Lachlan McCaw. ISBN: 978-1-921605-56-7 (pdf) Series: CAWCR technical report ; 20. Enquiries should be addressed to: Dr Graham A. Mills Centre for Australian Weather and Climate Research: A partnership between the Bureau of Meteorology and CSIRO GPO Box 1289, Melbourne Victoria 3001, Australia [email protected] Copyright and Disclaimer © 2010 CSIRO and the Bureau of Meteorology. To the extent permitted by law, 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 and the Bureau of Meteorology. CSIRO and the Bureau of Meteorology advise that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO and the Bureau of Meteorology (including each of its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it. Contents Abstract..........................................................................................................................1 1 Introduction..........................................................................................................3 2 Data .......................................................................................................................4 2.1 Fire Events............................................................................................................... 4 2.2 Meteorological Data................................................................................................. 7 3 Fire Weather Stability Indices – The Haines Index ...........................................8 3.1 The mid-level Haines Index .................................................................................... 10 3.2 A continuous Haines Index..................................................................................... 15 4 Relationship between C-HAINES and FFDI .....................................................20 5 Alternative fire weather stability indices .........................................................23 5.1 An energy perspective............................................................................................ 23 5.2 Depth of the mixed layer......................................................................................... 23 5.3 Stability of the entrainment layer ............................................................................ 24 5.4 A case-study example ............................................................................................ 24 6 Instability indices at fire locations ...................................................................27 7 Case study assessment ....................................................................................29 7.1 Fire activity under low or decreasing FFDI............................................................. 29 7.2 Nocturnal Breakouts ............................................................................................... 30 7.3 Association of high values of C-HAINES and weak overnight relative humidity recovery .................................................................................................................. 30 7.4 Penetration of frontal inversions ............................................................................. 32 7.5 Small-scale atmospheric circulation features......................................................... 32 7.6 Ingredients-based assessment .............................................................................. 32 7.7 Pyrocumulus events ............................................................................................... 33 8 Discussion..........................................................................................................34 9 Acknowledgements ...........................................................................................36 10 Rererences .........................................................................................................37 Appendix 1...................................................................................................................41 Appendix 2 – Case Studies ........................................................................................49 A.1 The Bluegum Plantation Fire .................................................................................. 50 A.2 The Billo Road and the Mount David Fire .............................................................. 57 A.3 Randall Block (Perth Hills) Fire – 15 October 2005 ............................................... 72 A.4 The Hovea Fire ....................................................................................................... 78 i A.5 The Pickering Brook Fire (Perth Hills 15-25 January 2005) ..................................82 A.6 The Denbarker Block Fire.......................................................................................91 A.7 The Lake Tay Fire.................................................................................................101 A.8 The Big Desert Fire of December 2002................................................................106 A.9 Victorian Fires 2006-7...........................................................................................112 A.10 The Scamander / St Mary’s Fire of 10-14 December 2006..................................122 A.11 The Berringa Fire of 25 February 1995 ................................................................127 A.12 The Mt Cooke Fire of 9-10 January 2003.............................................................137 A.13 Cobaw State Forest Prescribed Burn ...................................................................145 ii Atmospheric stability environments and fire weather in Australia – extending the Haines Index ABSTRACT The characteristics of the Haines Index, used to link vertical atmospheric stability and humidity with erratic fire behaviour, are examined for locations covering the majority of the areas of southern Australia that are subject to bushfires. It is shown that the index, originally developed for conditions in the north-west of the United States, is not configured to identify the most extreme conditions in Australia due to the different temperature lapse and humidity climatology of the two continents. An alternative extended version of the index is proposed, and along with a number of other measures of atmospheric stability, is compared with the fire danger index on a number of days of extreme or unexpected fire activity, and also for a number of days on which marked pyrocumulus cloud development was noted. While more quantitative comparison with fire behaviour data is required, the results suggest that the use of this extended Haines Index, C- HAINES, may provide additional and independent information to that provided by the traditional fire danger indices, particularly in conditions where unexpected night-time flare-ups of going fires have occurred, as well as in a number of cases of prescribed burns where fire behaviour was unexpectedly active. A number of case studies are presented in Appendix 2. 1 2 Atmospheric stability environments and fire weather in Australia – extending the Haines Index 1 INTRODUCTION It has long been believed amongst fire behaviourists that low- to mid-tropospheric atmospheric instability affects fire behaviour. The simplest conceptual model of this hypothesis is the “plume dominated” fire, where, in low wind conditions, a less stable atmosphere allows a deep convective column to develop, with the stronger updrafts in this column leading to stronger low-level inflow to the fire providing a positive feedback to fire activity (Byram 1954,1959, Luke and McArthur 1978, Rothermel 1991). Rothermel (1991) also proposed that pyrocumulus clouds, more likely in an unstable atmosphere, can lead to abrupt changes in fire behaviour due to downbursts triggered by evaporation of precipitation from those clouds, while other authors have proposed more direct circulation linkages between pyrocumulus clouds and fire behaviour (eg Tolhurst and Chatto 1999). In the most extreme circumstances pyrocumulus clouds