Implications of changing climate and atmospheric CO₂ for grassland fire in south-east Australia: Insights using the GRAZPLAN grassland simulation model

Climate and fuel characteristics influence fire regimes, and both need to be realistically considered in bushfire projections. Previous south-eastern Australian studies have assumed maximum grassland fuel curing (100%) and average fuel load (4.5tha-1). This study is the first to include daily fuel curing and load dynamics, derived from the agricultural pasture growth model GRAZPLAN, in projections of Grassland Fire Danger Index (GFDI) and potential fire-line intensity for future climateCO2 combinations, and for alternate grasslands in the Canberra, Sydney and Melbourne regions. Climate-change projections were characterised by warmer, drier conditions, with atmospheric CO2 concentrations increasing for longer future timeframes. Projected shifts in GFDI and potential fire-line intensity arising from future climateCO2 combinations were small compared with initial difference arising from using realistic GRAZPLAN-derived curing and fuel load values (compared with constant curing and fuel load) for grass dynamics, and this has important implications for the interpretation of earlier studies. Nevertheless, future grass curing and GFDI generally increased and fuel load generally decreased. The net effect on modelled future fire-line intensity was minimal because higher fire danger, and hence spread rate, was often largely compensated for by lower fuel load across the range of modelled grassland types and locations.