Sensitivity of Simulated Fire-Generated Circulations to Fuel
Characteristics During Large Wildfires
Abstract
Coupled fire-atmosphere models often struggle to simulate important fire
processes like fire generated flows, deep flaming fronts, extreme
updrafts, and stratospheric smoke injection during large wildfires. This
study uses the coupled fire-atmosphere model, WRF-Fire to examine the
sensitivities of some of these phenomena to the modeled surface fuel
load. Specifically, the 2020 Bear Fire and 2021 Caldor Fire in
California’s Sierra Nevada are simulated using three fuel loading
scenarios (1x, 4x, and 8x LANDFIRE derived surface fuel), while
controlling the fire rate of spread, to isolate the fuel loading needed
to produce fire-generated flows and plume rise comparable to NEXRAD
radar observations of these events. Increasing fuel loads and
corresponding fire residence time in WRF-Fire leads to deep plumes in
excess of 10 km, strong vertical velocities of 40-45 m s-1, and
combustion fronts several kilometers in width (in the along wind
direction). These results indicate that LANDFIRE-based surface fuel
loads in WRF-Fire likely under-represent fuel loading, having
significant implications for simulating landscape-scale wildfire
processes, associated impacts on spread, and fire-atmosphere feedbacks.