Modeling Canadian wildland fire carbon emissions with the Boreal Fire Effects (BORFIRE) model

Abstract

Wildland fires in Canada burn an average of2.8 million hectares of forest annually. In years of extreme forest fire activity. total carbon emissions from wildland fires approach levels similar to industrial carbon emissions. Quantifying annual wildland fire carbon emissions is required for Canada to meet its international reporting obligations. Carbon emission rates within a fire vary considerably due to fire behaviour within the burn perimeter. Large fires typically burn a wide range of fuel types under weather conditions that change as the fire spreads across the landscape. This causes huge spatial and temporal variation in fuel consumption. which is directly related to carbon emissions. To capture spatial and temporal variability. the Boreal Fire Effects (BORFIRE) model estimates carbon emissions using detailed fuel and weather data. BORFIRE is initialized with forest inventory data to establish preburn fuel loads for forest stand components. including live tree material (coarse roots. fine roots. stemwood. branchwood, foliage). standing dead trees (stemvI'ood. branchwood). dead and downed wood (coarse woody debris, medium woody debris). and forest floor organic matter (surface litter. duff). Carbon loss from each component is based on fuel consumption. which is calculated using fuel-specific fire behaviour models and burning conditions quantified by the Canadian Forest Fire Weather Index (FWI) System. Fire rate of spread is determined using the Initial Spread Index (lSI) of the FWI System and rate of spread algorithms of the Canadian Forest Fire Behavior Prediction System. This is combined with surface fuel consumption to calculate surface fire intensity using Byram's equation. I l' surface fire intensity exceeds the crown fire threshold. fuel consumption of aerial fuels is calculated. After determining carbon emissions. BORFIRE calculates the carbon transfers between stand components. BORFIRE has been incorporated as a submodel in the Canadian Wildland Fire Information System (CWFIS). and procedures have been developed to link CWFIS with the Carbon Budget Model of the Canadian Forest Sector to operationally calculate carbon emissions for Canadian wildland tires.