Temporal patterns of burned area in the Brazilian biomes

Fire, a dual-edged phenomenon, holds the potential for both harm and benefit to individuals and ecosystems contingent on its location, timing, and manner of occurrence. The expansion of human civilization has positioned it as the main source of fire ignitions on the Earth, fundamentally altering natural fire regimes. Ecosystems exhibit different responses and susceptibilities to fire, with impacts varying based on specific ecosystem characteristics. Across the  Brazilian landscapes, distinct biomes such as Cerrado, Pampa, and Pantanal are classified as fire-dependent. In contrast, forest-dominated biomes like the Atlantic Forest and Amazon are deemed fire-sensitive, while the Caatinga, despite limited research on its historical fire relationship, is tentatively categorized as fire-independent.

Brazil has witnessed unprecedented wildfires in recent decades, with natural fire regimes undergoing modification due to human activities, frequently tied to land-use and its changes practices or exacerbated by climate extremes associated with global warming. In this context, our goal was to characterize the temporal patterns of fires in Brazilian biomes, using a burned area dataset obtained from the Global Fire Atlas (2003-2018). This dataset tracks the daily dynamics of individual fires, and our analysis focused on the burned area extent.

In Brazil, over the time series (2003-2018), the peak years regarding the extent of burned areas were 2010, 2007 and 2012, totalling 392,057 km², 382,163 km², and 249,596 km², respectively. 2010 and 2007 presented an increase of ~240% above the mean, while 2012 an increase of ~150% above the mean.

Regarding the intra-annual fire patterns, observations revealed that Fire-sensitive biomes, in the Amazon and Atlantic Forest, the fire season was well-defined in two months, specifically August and September, representing, on average, 55% (4,058 km²) and 40% (1,027 km²) of the total burned area, respectively. In the Fire-independent biome, Caatinga, the fire season was prominent in September and October, constituting 67% (436 km²) of the total burned area. In relation to Fire-dependent biomes, Cerrado and Pantanal exhibited a concentrated fire season in August and September, accounting for 57% (10,283 km²) in Cerrado and 68% (900 km²) in Pantanal. Finally, Pampa's fire season displayed a heterogeneous configuration over time, making it impossible to extract a specific pattern of fire season.

In general, August and September of 2010 were the months that presented the greatest extent of burned area in the time series, in almost all biomes, except Pantanal and Pampa. The occurrence of fires, often caused by human actions, also can be associated with mega-droughts and ocean circulations such as the El Niño-Southern Oscillation (ENSO) event. The widespread occurrence of fires in 2010 can be attributed to the severe and unique drought that occurred as a consequence of the ENSO, affecting mainly Cerrado and Amazon.

In summary, the intensification of extreme events and the increase of fire source ignitions, even in fire-dependent environments, is affecting the Brazilian ecosystems, which presents distincts behavior and resilience in relation to fire events. Therefore, understanding the period of fire season is essential to develop command-and-control approaches and to fire prevention.