The evolution of the Brazilian savannahs' fire regimes under large-scale land use expansion and climate change

The BrazilianCerrado is the second largest biome in South America and the most extensive tropical savannah of the world[1]. Thisbiome is considered a world biodiversity hotspot [2]and plays an important role in the hydrology of Brazil[3]. However, despite its ecological importance,since the 1970sover 50% of the Cerrado has been transformed to agricultural lands[3]. Savannahs are fire-adapted ecosystems that dependon this natural disturbanceagentfor their functioning and continuity[1, 4].A range of climatic, environmental and anthropogenicfactorsshape fire regimes with potentialimpacts onbiodiversityandbiogeochemical cycles, andimportant socioeconomic consequences[5, 6]. In particular, humansmodify fire regimes primarily through the creation of ignitions, the fragmentation of ecosystems or the adoption of fire-suppression policies[7]. Furthermore, land-use expansion may also indirectly affect firesthrough the modification of local climatic and hydrological conditions associated to deforestation and vegetation substitution[8].Recent studiesin SouthernAfricasuggest that differentdrivers of fireactivitymay predominate at different temporal and spatial scalesand thatdiffering levels ofhuman presencemay explain the opposing trendsin burned area sizeobserved in different regions[6, 9].Remote sensing techniques are widely used to study fire regimesas they can offer larger temporal and spatial coverage than is often available from field studies or government agencies[10].In the Brazilian savannahs, studies usingsatellite datahave characterised different aspects of thefire dynamicsusingglobal burned area products[5, 11]or creatingtheir own datasets[12, 13]. However, these investigationsonly focus onrelations between firepatterns andclimatic drivers and do not considerland-use effects. In addition, either these studiescover short time periods, potentially hampering the identification of trends against inter-annual variability[9],or they cover longer periods but are restricted to specific areas of the Cerrado.In the next decades, agricultural expansionin these savannahsis expected to continuein responsetoglobal demand for meat and crops[3]. Simultaneously, as climate change progresses, extreme events like droughts and heatwaves may become more frequent. Considering the importance of the Cerrado,it is crucial to understand how fire regimes, anthropogenicactivities and the climate interactand affect these savannahs to inform land management practices, land regulationsand conservation policies.I aim to study Cerrado's fire regimes and their relation with anthropogenic and climatic drivers to understandand predicthow they may evolve under increasing land use pressure and climate change. I intend to study these processes for the entirety of these tropical savannahs spanning most of the period of large-scale agricultural expansion to present.