The Duff Moisture Code and the limits of sustainable combustion: examining the evidence for a widely used threshold

Mike Wotton; Melanie Wheatley

doi:10.1071/WF24164

RESEARCH ARTICLE (Open Access)

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The Duff Moisture Code and the limits of sustainable combustion: examining the evidence for a widely used threshold

Mike Wotton ^A ^B ^* and Melanie Wheatley ^C

+ Author Affiliations

- Author Affiliations

^A Institute of Forestry and Conservation, John H. Daniels Faculty of Architecture, Landscape and Design, University of Toronto, Toronto, ON M5S 3B3, Canada.

^B Great Lakes Forestry Centre, Canadian Forest Service, Natural Resources Canada, Sault Ste Marie, ON P6A 2E5, Canada.

^C Ontario Ministry of Natural Resources, Aviation Forest Fire Emergency Services, Sault Ste Marie, ON P6A 6V5, Canada.

^* Correspondence to: mike.wotton@utoronto.ca

International Journal of Wildland Fire 34, WF24164 https://doi.org/10.1071/WF24164

Submitted: 26 September 2024 Accepted: 6 January 2025 Published: 23 January 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of IAWF. This is an open access article distributed under the Creative Commons Attribution 4.0 International License (CC BY).

Abstract

Background

Canadian fire managers rely on the value of the Duff Moisture Code (DMC) for estimating lightning ignition and sustained smouldering in ground fuels. A simple rule used widely operationally suggests that lightning does not ignite fires and smouldering is not sustainable until the DMC >20.

Aims

We examine the strength of evidence supporting this simple rule.

Methods

We used daily lightning, fire and weather data from 2000 to 2019 to estimate the probability of lightning fire ignition across a number of regions in Canada. We also examined datasets of forest floor consumption from experimental burns carried out in pine forests in Canada.

Key results

Neither the 20 years of lightning fire ignition data nor the observed forest floor consumption data reveal consistent signals of an ignition threshold at or around DMC = 20.

Conclusions and Implications

Increasing DMC is associated with increasing probability of ignition from lightning and the extent of forest floor consumption, but there is little to no evidence to support the existence of a meaningful threshold across Canada when DMC is ~20. Users of this simple rule, be it for lightning ignition or fire perimeter extinction, should be aware that the data do not support a meaningful threshold around this value.

Keywords: fire extinguishment, fire ignition, fire management, fire occurrence prediction, fuel consumption, generalised additive modelling, lightning, lightning fire, smouldering combustion.

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