Fire trends on ATTO footprint over the last two decades

The Amazon Tall Tower Observatory is located in the central Amazon (S 02 08.9°, W 059 00.2°) inside the Uatumã Sustainable Development Reserve and has been monitoring continuously the atmospheric composition since 2013. The site is set up with two measurement towers of 80 meters and a tall tower of 325 meters for continuous monitoring of trace gases and aerosols. The surface influence (hereafter footprint) of the research station covers a large area to the east and northeast with the fetch extending for hundreds of kilometres, overlapping with the main branch of the Amazon River reaching the city of Belém (during the dry season) and large swaths of primary forest over the Amapá state (during the wet season).  We have analysed trends in fire counts (using MODIS thermal anomalies) and burned area (GFED4 and GFED5, Global Fire Emission Database 4th and 5th version) over the last two decades (2000-2023) inside the ATTO footprint and found that both show increasing and significant trends for the months of June (14,68 fire counts/year) July (42,23 fire counts/year), August (59,6 fire counts/year) and September (148,6 fire counts/year). Spatially, fires are located on easternmost part of the footprint and there is no evidence of a spatial trend approaching ATTO. Interestingly, in October the mean longitude of the fire counts over the period of interest shows a trend migrating from -56°W to -54°W, but with no significant trend in fire counts. We complement these results by analysing mole fractions of carbon monoxide (a proxy for biomass burning) at ATTO for an overlapping period (2013-2023). In addition, we provide links to the environmental drivers explaining these trends and spatial patterns. Observing biogenic greenhouse gases enhances our understanding of the Amazonian rainforest’s carbon budget, influenced by climatic conditions, land use alteration and other anthropogenic impacts.