Impact of climate change on the simulated global fire regime in an earth system model

Fire is an integral part of terrestrial ecosystem processes and it appears in the geological record soon after the appearance of terrestrial vegetation. However, fire is either absent or crudely represented in most global dynamic vegetation models and terrestrial ecosystem models. The Canadian Centre for Climate Modelling and Analysis (CCCma) first generation earth system model (CanESM1) includes fire as an interactive component of the climate system. Fire is modelled within the framework of the Canadian Terrestrial Ecosystem Model (CTEM) and all three aspects of the fire triangle namely the fuel availability, the readiness of fuel to burn depending on environmental conditions, and the presence of an ignition source are taken into account. The approach also represents anthropogenic effects on natural fire regimes, albeit in a simple manner. CTEM operates at a daily time step and burn area on a given day is calculated on the basis of probability of fire that depends on lightning frequency, root zone soil moisture and available biomass. Model results for the 1850-2000 period show that global annual burn area over the 20th century doesn't change significantly but shows large variability around its mean value of 3.4 million km2. This value can be compared with satellite-based burn area estimates that vary between 3 to 4 million km2 for the 1997-2004 period. For the 2001-2100 period simulated burn area increases from 3.4 to 3.8 million km2 with largest increases between 15 – 45 degrees north. Modelled global fire emissions for the 1850-2000 period are around 2.5 Pg C/yr compared to quasi-observation-based estimate of ~2.35 Pg C/yr for the 1999-2004 period. Over the 2001-2100 period modelled fire emissions increase from 2.5 to 2.75 Pg C/yr for the SRES A2 scenario.