Statistical Models of Ember Wash and Their Impact on Wildfire Area Growth

TL;DR

This paper introduces a stochastic model for near-surface ember transport, called ember wash, which influences wildfire spread differently from traditional plume-driven models, highlighting its significance in fire dynamics.

Contribution

The paper develops a novel probabilistic model for near-surface ember transport and demonstrates its impact on wildfire spread patterns through simulations.

Findings

Ember wash results in distinct spread behavior from classical models.

The model predicts an exponential distribution of ember flight times.

Simulations show ember wash can explain alternative wildfire spread regimes.

Abstract

Wildfire spread is strongly influenced by the transport and ignition of embers. While long-range spotting driven by plume lofting has received significant attention, embers transported near the surface by turbulent winds can also influence fire propagation. We develop a stochastic model for near-surface ember transport, referred to as ember wash. The model represents ember motion as a sequence of short displacements analogous to saltation-like transport and incorporates a probabilistic ignition process that depends on ember survival during transport. This formulation leads to an exponential distribution of ember flight times. The model is implemented within a simplified fire spread model to examine burn patterns and growth dynamics. Simulations demonstrate that ember wash produces spread behavior that differs fundamentally from classical plume-driven spotting. These results suggest that ember wash provides a plausible mechanism for wildfire spread regimes that differ from those predicted by geometric or plume-driven spread models.