Human ignitions dominate the fire regimes of the Brazilian Cerrado

Abstract Before human settlement, lightning was the predominant ignition source shaping the expansion of fire-adapted savannas and grasslands such as the Cerrado. However, humans have since altered ignition frequency, timing and intensity of fires, further influencing these ecosystems. Even though humans are considered the main cause of fires in the tropics, no study has quantitatively disentangled the relative contributions of lightning and human ignitions across the entire Cerrado. Here, we present a region-wide assessment of lightning and human-caused fire regimes, linking individual fire events and lightning occurrence through an attribution algorithm. We show that humans account for nearly 90% of ignitions, effectively redefining the natural fire regime of the Cerrado. Lightning ignitions peak during the dry-to-wet transition, whereas humans ignite fires throughout the dry season extending its duration threefold. Further, humans disproportionately drive fires with extreme behaviour, which have outsized ecological impacts, by igniting fires about ten times larger or two times more intense than lightning. These findings highlight the dominant role of humans in shaping Cerrado fire regimes, with profound implications for biodiversity conservation, ecosystem resilience and carbon cycling in tropical savannas, stressing the need for fire management policies that differentiate between traditional, prescribed and agricultural ignitions.