Key finding
The team analyzed approximately 175,000 Landsat images from 1986 to 2023 to reconstruct fire histories across the entire Gran Chaco region at 30-meter resolution. They found that roughly 65% of the Chaco, more than 70 million hectares, has experienced burning since 1985. The fire types are overwhelmingly anthropogenic: 70% are clearing fires (natural vegetation burned and then converted to agriculture within three years), 28% are management fires (on existing cropland or pasture), and only 2% are natural or other fires.
The link to drought is more complex than commonly assumed. Drought amplifies agricultural fires: during drought years, clearing fire burned area was about 5% higher than during non-drought years, because drier conditions make land clearing cheaper and more effective. But non-land-use fires actually declined with increasing precipitation deficit. The authors note that this challenges the widespread notion that intensifying droughts are a principal driver of changing fire regimes in tropical woodlands and savannahs.
Fire trends tracked deforestation trends closely. Argentina and Paraguay saw peak fire activity in the early to mid-2000s, matching their peak deforestation periods. Bolivia had low fire activity until a recent increase. Management fires on pastures became more prevalent after 2015, accounting for 42% of fires in Argentina, 23% in Paraguay, and 5% in Bolivia during 2015-2023. These management fires are used to control shrub encroachment on cattle pastures and increase during drought, making them a growing and underappreciated source of emissions.
What the research asks
Fire in the South American Gran Chaco, one of the world's most threatened subtropical woodlands and a major deforestation hotspot, is a subject of intense public and policy concern, especially as drought conditions intensify under climate change. But the fundamental question of whether fires in the Chaco are primarily driven by climate or by human land use has remained unanswered at the landscape scale. This study asked: what is the relative contribution of drought versus agricultural expansion to fire activity across the entire Gran Chaco, and how does drought interact with different types of human-set fires, from intentional clearing burns to pasture management fires?
What it finds
The team analyzed approximately 175,000 Landsat images from 1986 to 2023 to reconstruct fire histories across the entire Gran Chaco region at 30-meter resolution. They found that roughly 65% of the Chaco, more than 70 million hectares, has experienced burning since 1985. The fire types are overwhelmingly anthropogenic: 70% are clearing fires (natural vegetation burned and then converted to agriculture within three years), 28% are management fires (on existing cropland or pasture), and only 2% are natural or other fires.
The link to drought is more complex than commonly assumed. Drought amplifies agricultural fires: during drought years, clearing fire burned area was about 5% higher than during non-drought years, because drier conditions make land clearing cheaper and more effective. But non-land-use fires actually declined with increasing precipitation deficit. The authors note that this challenges the widespread notion that intensifying droughts are a principal driver of changing fire regimes in tropical woodlands and savannahs.
Fire trends tracked deforestation trends closely. Argentina and Paraguay saw peak fire activity in the early to mid-2000s, matching their peak deforestation periods. Bolivia had low fire activity until a recent increase. Management fires on pastures became more prevalent after 2015, accounting for 42% of fires in Argentina, 23% in Paraguay, and 5% in Bolivia during 2015-2023. These management fires are used to control shrub encroachment on cattle pastures and increase during drought, making them a growing and underappreciated source of emissions.
Why it matters
This paper provides a critical evidence base for fire management and deforestation monitoring in one of the world's most threatened subtropical regions. The finding that fire in the Chaco is overwhelmingly anthropogenic and land-use-driven, not climate-driven, has direct implications for policy. Argentina's Law 26.815 banning cropland fires and Paraguay's strict fire controls could reduce fire risk, but enforcement depends on knowing where and when fires are occurring. Satellite-based near-real-time fire monitoring systems can provide that intelligence.
For earth observation practitioners, the study's use of 30-meter Landsat data spanning nearly four decades demonstrates that long time-series analysis remains essential for understanding fire regimes, even as higher-resolution data becomes available. The finding that management fires on pastures are the second largest source and increase during drought points to a monitoring gap that satellite systems could fill: detecting and attributing small, recurrent management fires that are easily overlooked in global fire products.
For carbon market developers and REDD+ project proponents in the Gran Chaco, the paper offers crucial context. Forest carbon projects need to account not just for deforestation but also for degradation from recurrent pasture management fires. And the anthropogenic nature of Chaco fires means that effective fire management is both a mitigation opportunity and a verifiable conservation outcome.