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Fire behaviour case study of two early winter grass fires in southern Alberta, 27 November 2011

Author(s): Martin E. Alexander, Mark J. Heathcott, Randall L. Schwanke
Year Published: 2013
Description:

On November 27, 2011, two wildfires - the Lethbridge Fire and the Milk River Ridge Fire - starting within approximately an hour of each other, advanced in a north-easterly direction some 12 km and 32 km, respectively, from their point of origin in a relatively short period of time. Fortunately, no lives were lost. However, a few home properties were destroyed in the Lethbridge Fire. Similar threatening occurrences have taken place in the past and subsequently. The purpose of this report is to provide a detailed account of the behaviour of these two fires in relation to their associated environment (i.e., fuels, weather, and topography) and accordingly examine the implications for human safety and wildland fire protection in the southern region of Alberta. From our analysis of these two wildfire incidents, the following "facts" emerge: (1) While lightning-ignited fires occasionally occur on the Canadian prairies, both of these fires were suspected of being caused by human carelessness (although not of a malicious nature) and thus, technically preventable. (2) A lack of snow cover in early winter exposed fully-cured grassland and agriculture cropland fuels, thus leaving the landscape susceptible to fire spread. Once the Chinook winds commenced (southwest, greater than 60 km/h), the only remaining ingredient needed for a major fire run to take place was an ignition source. (3) Considering the fuel and weather conditions, grass or crop fires are capable of quickly achieving forward spread rates of 8 km/h and producing flame heights of 3 metres at the leading edge or "head" of the fire front. In these situations, the rate of fire growth easily overwhelms the capability of any fire suppression force. A 30 metre or 100 feet plus barrier to fire spread and/or a significant drop in the strength of the winds would be required to stop such a fire's headlong assault. (4) From an analysis of the historical weather records for the Lethbridge area and existing models for predicting particular aspects of grassland fire behaviour, the fuel and weather conditions that prevailed on November 27, 2011, happen far more often than one would think. With this recurring potential for fire spread, the only missing ingredient for a large, fast spreading wildfire incident to occur is some form of ignition which is ever present in the fire environment (i.e., people). A monitoring and early warning system for grassland fire danger that meets the needs of the general public and emergency services coupled with education and training is required to avert the potential for any future wildfire disasters.

Citation: Alexander, M.E.; Heathcott, M.J.; Schwanke, R.L. 2013. Fire behaviour case study of two early winter grass fires in southern Alberta, 27 November 2011. Partners in Protection Association, Edmonton, Alberta. T6H 3S5. 76 p.
Topic(s): Fire Behavior, Extreme Fire Behavior, Case Studies
Ecosystem(s): Lower montane/foothills/valley grassland
Document Type: Technical Report or White Paper
NRFSN number: 11995
FRAMES RCS number: 15209
Record updated: Jun 14, 2018