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Assessing dependence between frequency and severity through shared random effects.

Devan G Becker1, Douglas G Woolford1, Charmaine B Dean2

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This study introduces a new framework to model wildland fire frequency and severity together. Findings reveal negative dependence for lightning-caused fires and positive dependence for person-caused fires, offering insights into fire behavior dynamics.

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Area of Science:

  • Environmental Science
  • Statistical Modeling
  • Ecology

Background:

  • Wildland fire research often models fire occurrence and size separately.
  • Existing models lack a unified approach to capture the relationship between fire frequency and severity.

Purpose of the Study:

  • To develop and apply a compound process framework for jointly modeling wildland fire frequency and severity.
  • To estimate the relationship between fire occurrence and size, accounting for spatial and temporal dependencies.

Main Methods:

  • A shared random effect links separate models for fire frequency and size.
  • Exploration of spatial and temporal autocorrelation of random effects.
  • Joint estimation to share information between frequency and size models.

Main Results:

  • A negative dependence was found between frequency and size for lightning-caused fires.
  • A positive dependence was observed for person-caused fires.
  • A simple test for independence using credible intervals proved powerful.

Conclusions:

  • The compound process framework effectively models the interdependence of wildland fire frequency and severity.
  • Understanding these dependencies is crucial for accurate wildland fire prediction and management.
  • The model provides insights into factors influencing fire behavior based on ignition source.