Towards mechanistic representation of wildfire effects on soil – downscaling to quantify subsurface heat fluxes

Advances in wildfire modeling have focused on refining atmospheric interactions for obvious links between local airflows, combustion dynamics, fire line advance and smoke plume transport. Yet, lasting impacts of wildfires on landscapes are linked primarily with changes in soil characteristics and alteration of ecological and hydrologic processes. Quantitative assessment of wildfire impacts requires metrics for fire-surface thermal interactions beyond qualitative surrogates such as burn severity used for ecological assessment. The highly transient and localized nature of wildfire intensity and its coarse spatial and temporal representation hinder quantitative translation of wildfire dynamics to soil heat fluxes even with the most advanced wildfire models (e.g., QuicFire, WRF-Fire, WFDS). Inspired by the pioneering works of Byram, Rothermel and Albini, we seek to derive high resolution information on fire line intensities from highly resolved fuel maps informed by fire line dynamics derived from numerical wildfire model representation. This hybrid downscaling approach (limited by the quality and resolution of fuel maps) offers a means for constraining soil surface heat fluxes at resolutions relevant to quantifying critical temperatures and duration at depth to estimate pyrolysis of soil organic carbon and the degree of soil structure alteration. Examples will be presented and discussed.