Exploring the Effect of Fuels and Forest Structure on Daily Emissions and Smoke Production from the Rim Fire

2018 has been called the most destructive fire season in California history, with thousands of homes burned and many metropolitan areas formerly unaccustomed to "unhealthy" or worse levels of wildfire smoke experiencing such levels for days on end, far from the wildland urban interface and the smoke sources. A significant characteristic of some recent megafires has been a rapid rate of spread and the subsequently large daily emissions produced by such fire behavior. But exactly how exceptional are the daily emissions numbers we are seeing today, both in the context of the last couple decades and in the context of historical emissions that California experienced? How much lighter were the fuels and what difference would the lighter fuels loads and lower tree densities have made in the daily loading to the atmosphere? This work leverages recent advances in spatial analysis frameworks that unify plot-to-landscape imputation of fuel loads, fire emissions estimation, and coupled atmosphere-wildland fire modeling to explore how the daily progression and emissions from the Rim Fire might have been different had fuels and forest structure in the area been maintained by an active fire regime. Specifically, we use the F3 fuels mapping framework to find biophysically analogous areas nearby that have experienced one or more fire returns in the last 30 years and create a "treated fuelbed" for the area burned by the Rim Fire. Using this "treated fuelbed" and the actual fuelbeds as model inputs, we examine modeled Rim fire growth and behavior using the CAWFE coupled atmosphere-wildland fire model, and we explore the extent to which present-day fuel (vs. our estimated historical) loadings might have contributed to the fire-atmosphere coupling that produces such unprecedented large-scale fire behavior and daily pollutant emissions values witnessed in the Rim (and likely other Sierra megafires).