Fires during recent El Niño and La Niña periods in Eastern Amazon

Anomalies in sea surface temperature of the tropical Pacific Ocean, are associated with changes in precipitation and humidity patterns in the Amazon region. Temperature increases (El Niño) causes abnormal dry seasons, making the forest more susceptible to wildfires. The decrease (La Niña) in ocean temperatures implies abnormal increases in rainfall, especially in the northern region of Amazon. Between 2019 and 2024, the municipality of Santarém (Pará, Brazil), eastern Amazon, was affected by an increase in forest fires, leading the local government to declare an environmental emergency state in 2024. The objective of this study was to characterize burned areas and changes in land cover in Santarém during the recent ENSO period (2019 to 2024). Annual data on Land Use and Land Cover (LULC) from MapBiomas (Collection 10), and monthly data of burned area from MapBiomas Fogo (Collection 4) were used. National Oceanic and Atmospheric Administration's (NOAAs) Weather Prediction Center data was used to define El Niño (EN), La Niña (LN) and “no anomalies” months (Regular - Rg). LULC was analyzed in small properties (SMp > 300 hectares (ha)), medium-sized (MS, 300 to 1125 ha), large properties (LP >1125 ha), and smallholdings (SMs < 300 ha), as well as indigenous lands (ILs), quilombola areas (Qa), and conservation units (Cs). These data were extracted from SICAR (National Rural Environmental Registry System). For EN periods, 19 months between 2019 and 2024 were analyzed, with 62,962.56 ha of burned areas. For LN (28 months), 15,799.59 ha were burned. During Rg (25 months), 60,109.20 ha of burned area were detected. During EN and Rg periods, Forest Formation (FF) was the most affected coverage, with 36,016.92 ha (EN, 57%) and 39,183.03 (Rg, 65%). For LN, the highest burned coverage was Pasture (Pt), with 8,537.94 ha burned. Mostly small properties (SMp) were affected, with 1,249.29 ha (EN) and 1,124.82 ha (Rg) of FF scorched (1.87%). Pt areas were also affected in SMp (2.07%), accounting for 4.84% of the total. For the protected areas, Cs had 5.63% of the total burned area, with 3,913.47 ha (EN), 2,574.09 ha (Rg) and 1,330.56 ha (LN), mostly in FF. ILs had 1.04% of the total, mostly during EN, with 1,287.27 ha. Other classes (MS, LP, SMs and Qa) accounted for only 1.06% of the burned area. Areas without SICAR classification had the largest burned area (87.43% of the total). These patterns raise concern, given that burning persists in forest areas that remain unprotected and unmonitored. The occurrence of climatic phenomena that induce drier vegetation and less precipitation in the Amazon enable increases in  burned area associated with anthropic activities. Implementing fire-prevention measures in vulnerable areas is crucial, and it is equally important to account for these climatic periods. Investment in public policies for environmental education and fire mitigation are essential for transforming these scenarios, in order to mitigate the effects of climate change.