Rising vapor pressure deficit and fuel availability exacerbate the dispersion of intra-annual burned area

Abstract

Continuing climate warming is creating more favorable burning conditions both within and outside the core fire seasons, such as drier vegetation, increased fuel load, and more frequent lightning. These changes are expected to reshape wildfire regimes, with profound implications for wildfire management practices and the terrestrial carbon cycle. However, limited knowledge exists regarding how the seasonal regimes of wildfires respond to continued warming and what consequences this has for fire-related carbon emissions. Our analysis of satellite-derived burned area data reveals a widespread increase in the dispersion of burned area, particularly in most regions of Eurasia, South America, and Australia. Nonetheless, estimates based on the fire weather index tend to underestimate these increases. This increasing dispersion of burned area is primarily driven by increased vapor pressure deficit and fuel availability, which promote more burned areas outside the core fire season. Nevertheless, the increased dispersion of burned area does not lead to a synchronous rise in the dispersion of fire-related carbon emissions. This decoupling occurs because carbon emission per unit of burned area significantly rises within the core fire season but insignificantly changes outside it. Our results highlight the critical role of warming in reshaping seasonal wildfire regimes and have important implications for wildfire management and global carbon budget estimation.