Modelling the role of fires in the terrestrial carbon balance by incorporating SPITFIRE into the global vegetation model ORCHIDEE – Part 2: Carbon emissions and the role of fires in the global carbon balance

Abstract

International audienceCarbon dioxide emissions from wild and anthropogenic fires return the carbon absorbed by plants to the atmosphere, and decrease the sequestration of carbon by land ecosystems. Future climate warming will likely increase the frequency of fire-triggering drought, so that the future terrestrial carbon uptake will depend on how fires respond to altered climate variation. In this study, we modelled the role of fires in the global terrestrial carbon balance for 1901–2012, using the ORCHIDEE global vegetation model equipped with the SPITFIRE model. We conducted two simulations with and without the fire module being activated, using a static land cover. The simulated global fire carbon emissions for 1997–2009 are 2.1 Pg C yr−1, which is close to the 2.0 Pg C yr−1 as estimated by GFED3.1. The simulated land carbon uptake after accounting for emissions for 2003–2012 is 3.1 Pg C yr−1, which is within the uncertainty of the residual carbon sink estimation (2.8 ± 0.8 Pg C yr−1). Fires are found to reduce the terrestrial carbon uptake by 0.32 Pg C yr−1 over 1901–2012, or 20% of the total carbon sink in a world without fire. The fire-induced land sink reduction (SRfire) is significantly correlated with climate variability, with larger sink reduction occurring in warm and dry years, in particular during El Niño events. Our results suggest a "fire respiration partial compensation". During the 10 lowest SRfire years (SRfire = 0.17 Pg C yr−1), fires mainly compensate for the heterotrophic respiration that would occur in a world without fire. By contrast, during the 10 highest SRfire fire years (SRfire = 0.49 Pg C yr−1), fire emissions far exceed their respiration partial compensation and create a larger reduction in terrestrial carbon uptake. Our findings have important implications for the future role of fires in the terrestrial carbon balance, because the capacity of terrestrial ecosystems to sequester carbon will be diminished by future climate change characterized by increased frequency of droughts and extreme El Niño events

Generation of a global fuel data set using the Fuel Characteristic Classification System

“…We selected diverse products for the comparison of the fuelbeds' biomass, which were generated employing different methods. As a global biomass product, we used the map obtained by the Orchidee DGVM (Yue et al, 2015), because the biomass is calculated separately for different fuel strata, and we were able to select the layers that corresponded to the fuel strata from the fuelbeds, hence obtaining comparable results. Although there is a global biomass product currently available (Ruesch and Gibbs, 2008), it includes data of both living above and below (root) ground biomass.…”

“…Cells with homogeneous land cover types (> 80 % of the cell) were selected for the comparison exercise. The following biomass products were compared with our estimations: -Global biomass from the Orchidee Dynamic Global Vegetation Model (DGVM) (Krinner et al, 2005), as estimated from Yue et al (2015). The biomass was obtained from a vegetation distribution map classified into 13 plant functional types based on the IGBP vegetation map (Loveland et al, 2000).…”

Historic global biomass burning emissions for CMIP6 (BB4CMIP) based on merging satellite observations with proxies and fire models (1750–2015)

“…For the global vegetation model ORCHIDEE (Krinner et al, 2005), SPITFIRE was adjusted and incorporated by Yue et al (2014Yue et al ( , 2015. Most equations from the original SPIT-FIRE model were implemented and run parallel to the STO-MATE submodule, which simulated vegetation carbon cycle processes in ORCHIDEE.…”

ORCHIDEE-MICT (v8.4.1), a land surface model for the high latitudes: model description and validation

“…Note that this method only calibrated for mean annual regional burned area, and that simulated latitudinal distributions and grid cell spatial patterns of burned area and fire carbon emissions, and their interannual and seasonal variabilities, could still be compared with observationbased data. Deforestation and peatland fires are not explicitly simulated, but as both fire types rely on suitable weather conditions to occur, which could be partly captured by SPIT-FIRE (Yue et al, 2015), model simulations are expected to partially include these fire types.…”