A new framework for modeling fires and their interaction with ecosystems, the carbon cycle, land-use and climate mitigation strategies

Vegetation fires are an essential component of the Earth system, as a natural phenomenon maintaining heterogeneous and biodiverse landscapes, and as a widespread tool for landuse activities (e.g. deforestation, pasture maintenance). Fires play a key role in ecosystem dynamics and the carbon cycle, relevant from local to global scales, and are expected to be affected by changes in the climate and human systems. Yet accounting for fires in Earth system models is limited, providing little insights into future fire impacts and whether they could be mitigated. Here we identify 3 fundamental requirements for advanced fire modeling: 1/ a good understanding of fire drivers (e.g. climate, human activities, vegetation structure); 2/ a proper representation of their impacts through time and across vegetation characteristics (e.g. partial and size-dependent mortality, fate of dead material); and 3/ a modeling framework that can integrate these processes at the appropriate scale and that includes the dynamics of human activities. We then present a new fire model developed within the Ecosystem Demography model (ED), particularly well adapted to advanced fire modeling as it tracks the age, size and species structure within ecosystems, and is part of a coupled Human-Earth system framework (the integrated Ecosystem Demography model, iED) which provides future economic and land-use projections under a given climate mitigation policy. The model is first evaluated in the Amazon basin, where it reproduces patterns of both natural and land-use fires, and the overall carbon fluxes. We then explore future fire activity in iED and show that it will largely depend on climate policies and the resulting land-use patterns in the Amazon.