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 total fuel load and its consumption. 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 using observations. This approach helps isolate the fuel loading and consumption needed to produce fire-generated winds and plume rise comparable to 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.