International Journal of Wildland Fire International Journal of Wildland Fire Society
Journal of the International Association of Wildland Fire

Critical live fuel moisture in chaparral ecosystems: a threshold for fire activity and its relationship to antecedent precipitation

Philip E. Dennison A C and Max A. Moritz B
+ Author Affiliations
- Author Affiliations

A Department of Geography and Center for Natural and Technological Hazards, University of Utah, 260 S Central Campus Drive, Room 270, Salt Lake City, UT 84112 USA.

B Department of Environmental Science, Policy, and Management, Center for Fire Research and Outreach, University of California, Berkeley, 137 Mulford Hall 3114, Berkeley, CA 94720, USA. Email:

C Corresponding author. Email:

International Journal of Wildland Fire 18(8) 1021-1027
Submitted: 12 April 2008  Accepted: 3 June 2009   Published: 9 December 2009


Large wildfires in southern California typically occur during periods of reduced live fuel moisture (LFM) and high winds. Previous work has found evidence that a LFM threshold may determine when large fires can occur. Using a LFM time series and a fire history for Los Angeles County, California, we found strong evidence for a LFM threshold near 79%. Monthly and 3-month total precipitation data were used to show that the timing of this threshold during the fire season is strongly correlated with antecedent rainfall. Spring precipitation, particularly in the month of March, was found to be the primary driver of the timing of LFM decline, although regression tree analysis revealed that high winter precipitation may delay the timing of the threshold in some years. This work further establishes relationships between precipitation and fire potential that may prove important for anticipating shifts in fire regimes under climate-change scenarios.


The authors thank Tom Bristow and J. Lopez of the Los Angeles County Fire Department for providing the LFM data. The authors also thank the anonymous reviewers, whose comments helped us improve this paper.


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