Limiting global warming to 1.5 °C minimises projected global increases in fire weather days, but adaptation to new fire regimes is still needed

Abstract. Understanding future shifts in fire weather risk, including peak season, transitional and off-season, will be crucial for reshaping fire preparation and management in order to adapt to climate change. This study explores future climate-driven projections of fire weather using the McArthur Forest Fire Danger Index (FFDI) across three Global Warming Levels (GWLs) with two future emissions scenarios – 1.5 °C, 2.0 °C under both RCP2.6 and RCP8.5, and 4.0 °C under RCP8.5. Using a large, perturbed physics ensemble, we assess uncertainty in fire weather projections globally and for three regions: Australia, Brazil, and the USA. In addition to season length and peak FFDI, we evaluate transitions in meteorological fire danger periods and shifts in low-fire weather windows to inform fire management throughout the annual cycle. We project a global rise in fire weather days and severity at all GWLs, with the largest increases in Australia, followed by Brazil and the USA. At 1.5 °C, the area exposed to Very High fire weather (FFDI ≥ 24) expands by 31 % (25 %–36 %) relative to a baseline of 1986–2005. Higher GWLs drive further increases, with more than a threefold rise in Very High fire weather days from 2.0 °C to 4.0 °C, emphasising the mitigation benefits of limiting global warming to well below 2.0 °C as intended by the Paris Agreement. The transition from High to Very High, a proxy for the start of the fire season, advances, by 9–12 days in Australia, 16–22 days in Brazil, and 8–24 days in the USA. Despite these changes, low-fire windows persist, providing crucial opportunities for out-of-season preparation such as controlled burns. Our findings highlight the need for both emissions reductions and adaptive strategies, including accounting for changes in out-of-season fire risks when employing management techniques that rely on pre-fire season preparations.